From: Roberto Sassu roberto.sassu@huawei.com

Add a parser of a generic Type-Length-Value (TLV) format:

+-----------------+------------------+-----------------+ | data type (u64) | num fields (u64) | total len (u64) | # header +--------------+--+---------+--------+---------+-------+ | field1 (u64) | len1 (u64) | value1 (u8 len1) | +--------------+------------+------------------+ | ... | ... | ... | # data +--------------+------------+------------------+ | fieldN (u64) | lenN (u64) | valueN (u8 lenN) | +--------------+------------+------------------+

[same as above, repeated N times]

Each adopter can define its own data types and fields. The TLV parser does not need to be aware of those, but lets the adopter obtain the data and decide how to continue.

After parsing each TLV header, call the header callback function with the callback data provided by the adopter. The latter can return 0, to skip processing of the TLV data, 1 to process the TLV data, or a negative value to stop processing the TLV data.

After processing a TLV data entry, call the data callback function also with the callback data provided by the adopter. The latter can decide how to interpret the TLV data entry depending on the field ID.

Nesting TLVs is also possible, the data callback function can call tlv_parse() to parse the inner structure.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- MAINTAINERS | 8 ++ include/linux/tlv_parser.h | 48 +++++++ include/uapi/linux/tlv_parser.h | 62 +++++++++ lib/Kconfig | 3 + lib/Makefile | 2 + lib/tlv_parser.c | 221 ++++++++++++++++++++++++++++++++ lib/tlv_parser.h | 17 +++ 7 files changed, 361 insertions(+) create mode 100644 include/linux/tlv_parser.h create mode 100644 include/uapi/linux/tlv_parser.h create mode 100644 lib/tlv_parser.c create mode 100644 lib/tlv_parser.h

diff --git a/MAINTAINERS b/MAINTAINERS index 8766f3e5e87e..ba8d5c137bef 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -23055,6 +23055,14 @@ W: http://sourceforge.net/projects/tlan/ F: Documentation/networking/device_drivers/ethernet/ti/tlan.rst F: drivers/net/ethernet/ti/tlan.*

+TLV PARSER +M: Roberto Sassu roberto.sassu@huawei.com +L: linux-kernel@vger.kernel.org +S: Maintained +F: include/linux/tlv_parser.h +F: include/uapi/linux/tlv_parser.h +F: lib/tlv_parser.* + TMIO/SDHI MMC DRIVER M: Wolfram Sang wsa+renesas@sang-engineering.com L: linux-mmc@vger.kernel.org diff --git a/include/linux/tlv_parser.h b/include/linux/tlv_parser.h new file mode 100644 index 000000000000..6d9a655d9ec9 --- /dev/null +++ b/include/linux/tlv_parser.h @@ -0,0 +1,48 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Header file of TLV parser. + */ + +#ifndef _LINUX_TLV_PARSER_H +#define _LINUX_TLV_PARSER_H + +#include <uapi/linux/tlv_parser.h> + +/** + * typedef hdr_callback - Callback after parsing TLV header + * @callback_data: Opaque data to supply to the header callback function + * @data_type: TLV data type + * @num_entries: Number of TLV data entries + * @total_len: Total length of TLV data + * + * This callback is invoked after a TLV header is parsed. + * + * Return: 0 to skip processing, 1 to do processing, a negative value on error. + */ +typedef int (*hdr_callback)(void *callback_data, __u64 data_type, + __u64 num_entries, __u64 total_len); + +/** + * typedef data_callback - Callback after parsing TLV data entry + * @callback_data: Opaque data to supply to the data callback function + * @field: TLV field ID + * @field_data: Data of a TLV data field + * @field_len: Length of @field_data + * + * This callback is invoked after a TLV data entry is parsed. + * + * Return: 0 on success, a negative value on error. + */ +typedef int (*data_callback)(void *callback_data, __u64 field, + const __u8 *field_data, __u64 field_len); + +int tlv_parse(hdr_callback hdr_callback, void *hdr_callback_data, + data_callback data_callback, void *data_callback_data, + const __u8 *data, size_t data_len, const char **data_types, + __u64 num_data_types, const char **fields, __u64 num_fields); + +#endif /* _LINUX_TLV_PARSER_H */ diff --git a/include/uapi/linux/tlv_parser.h b/include/uapi/linux/tlv_parser.h new file mode 100644 index 000000000000..fbd4fc403ac7 --- /dev/null +++ b/include/uapi/linux/tlv_parser.h @@ -0,0 +1,62 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Implement the user space interface for the TLV parser. + */ + +#ifndef _UAPI_LINUX_TLV_PARSER_H +#define _UAPI_LINUX_TLV_PARSER_H + +#include <linux/types.h> + +/* + * TLV format: + * + * +-----------------+------------------+-----------------+ + * | data type (u64) | num fields (u64) | total len (u64) | # header + * +--------------+--+---------+--------+---------+-------+ + * | field1 (u64) | len1 (u64) | value1 (u8 len1) | + * +--------------+------------+------------------+ + * | ... | ... | ... | # data + * +--------------+------------+------------------+ + * | fieldN (u64) | lenN (u64) | valueN (u8 lenN) | + * +--------------+------------+------------------+ + * + * [same as above, repeated N times] + * + */ + +/** + * struct tlv_hdr - Header of TLV format + * @data_type: Type of data to parse + * @num_entries: Number of data entries provided + * @_reserved: Reserved for future use (must be equal to zero) + * @total_len: Total length of the data blob, excluding the header + * + * This structure represents the header of the TLV data format. + */ +struct tlv_hdr { + __u64 data_type; + __u64 num_entries; + __u64 _reserved; + __u64 total_len; +} __attribute__((packed)); + +/** + * struct tlv_data_entry - Data entry of TLV format + * @field: Data field identifier + * @length: Data length + * @data: Data + * + * This structure represents a TLV data entry. + */ +struct tlv_data_entry { + __u64 field; + __u64 length; + __u8 data[]; +} __attribute__((packed)); + +#endif /* _UAPI_LINUX_TLV_PARSER_H */ diff --git a/lib/Kconfig b/lib/Kconfig index b38849af6f13..9141dcfc1704 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -777,3 +777,6 @@ config POLYNOMIAL

config FIRMWARE_TABLE bool + +config TLV_PARSER + bool diff --git a/lib/Makefile b/lib/Makefile index 322bb127b4dc..c6c3614c4293 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -392,6 +392,8 @@ obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o

obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o +obj-$(CONFIG_TLV_PARSER) += tlv_parser.o +CFLAGS_tlv_parser.o += -I lib

# FORTIFY_SOURCE compile-time behavior tests TEST_FORTIFY_SRCS = $(wildcard $(src)/test_fortify/*-*.c) diff --git a/lib/tlv_parser.c b/lib/tlv_parser.c new file mode 100644 index 000000000000..5d54844ab8d7 --- /dev/null +++ b/lib/tlv_parser.c @@ -0,0 +1,221 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Implement the TLV parser. + */ + +#define pr_fmt(fmt) "tlv_parser: "fmt +#include <tlv_parser.h> + +/** + * tlv_parse_hdr - Parse TLV header + * @hdr_callback: Callback function to call after parsing header + * @hdr_callback_data: Opaque data to supply to the header callback function + * @data: Data to parse (updated) + * @data_len: Length of @data (updated) + * @parsed_num_entries: Parsed number of data entries (updated) + * @parsed_total_len: Parsed length of TLV data, excluding the header (updated) + * @data_types: Array of data type strings + * @num_data_types: Number of elements of @data_types + * + * Parse the header of the TLV data format, move the data pointer to the TLV + * data part, decrease the data length by the length of the header, and provide + * the number of entries and the total data length extracted from the header. + * + * Before returning, call the header callback to let the callback supplier + * decide whether or not to process the subsequent TLV data. + * + * Return: 1 to process the data entries, 0 to skip, a negative value on error. + */ +static int tlv_parse_hdr(hdr_callback hdr_callback, void *hdr_callback_data, + const __u8 **data, size_t *data_len, + __u64 *parsed_num_entries, __u64 *parsed_total_len, + const char **data_types, __u64 num_data_types) +{ + __u64 parsed_data_type; + struct tlv_hdr *hdr; + + if (*data_len < sizeof(*hdr)) { + pr_debug("Data blob too short, %lu bytes, expected %lu\n", + *data_len, sizeof(*hdr)); + return -EBADMSG; + } + + hdr = (struct tlv_hdr *)*data; + + *data += sizeof(*hdr); + *data_len -= sizeof(*hdr); + + parsed_data_type = __be64_to_cpu(hdr->data_type); + if (parsed_data_type >= num_data_types) { + pr_debug("Invalid data type %llu, max: %llu\n", + parsed_data_type, num_data_types - 1); + return -EBADMSG; + } + + *parsed_num_entries = __be64_to_cpu(hdr->num_entries); + + if (hdr->_reserved != 0) { + pr_debug("_reserved must be zero\n"); + return -EBADMSG; + } + + *parsed_total_len = __be64_to_cpu(hdr->total_len); + if (*parsed_total_len > *data_len) { + pr_debug("Invalid total length %llu, expected: %lu\n", + *parsed_total_len, *data_len); + return -EBADMSG; + } + + pr_debug("Header: type: %s, num entries: %llu, total len: %lld\n", + data_types[parsed_data_type], *parsed_num_entries, + *parsed_total_len); + + return hdr_callback(hdr_callback_data, parsed_data_type, + *parsed_num_entries, *parsed_total_len); +} + +/** + * tlv_parse_data - Parse TLV data + * @data_callback: Callback function to call to parse the data entries + * @data_callback_data: Opaque data to supply to the data callback function + * @num_entries: Number of data entries to parse + * @data: Data to parse + * @data_len: Length of @data + * @fields: Array of field strings + * @num_fields: Number of elements of @fields + * + * Parse the data part of the TLV data format and call the supplied callback + * function for each data entry, passing also the opaque data pointer. + * + * The data callback function decides how to process data depending on the + * field. + * + * Return: 0 on success, a negative value on error. + */ +static int tlv_parse_data(data_callback data_callback, void *data_callback_data, + __u64 num_entries, const __u8 *data, size_t data_len, + const char **fields, __u64 num_fields) +{ + const __u8 *data_ptr = data; + struct tlv_data_entry *entry; + __u64 parsed_field, len, i, max_num_entries; + int ret; + + max_num_entries = data_len / sizeof(*entry); + + /* Possibly lower limit on num_entries loop. */ + if (num_entries > max_num_entries) + return -EBADMSG; + + for (i = 0; i < num_entries; i++) { + if (data_len < sizeof(*entry)) + return -EBADMSG; + + entry = (struct tlv_data_entry *)data_ptr; + data_ptr += sizeof(*entry); + data_len -= sizeof(*entry); + + parsed_field = __be64_to_cpu(entry->field); + if (parsed_field >= num_fields) { + pr_debug("Invalid field %llu, max: %llu\n", + parsed_field, num_fields - 1); + return -EBADMSG; + } + + len = __be64_to_cpu(entry->length); + + if (data_len < len) + return -EBADMSG; + + pr_debug("Data: field: %s, len: %llu\n", fields[parsed_field], + len); + + if (!len) + continue; + + ret = data_callback(data_callback_data, parsed_field, data_ptr, + len); + if (ret < 0) { + pr_debug("Parsing of field %s failed, ret: %d\n", + fields[parsed_field], ret); + return ret; + } + + data_ptr += len; + data_len -= len; + } + + if (data_len) { + pr_debug("Excess data: %lu bytes\n", data_len); + return -EBADMSG; + } + + return 0; +} + +/** + * tlv_parse - Parse data in TLV format + * @hdr_callback: Callback function to call after parsing header + * @hdr_callback_data: Opaque data to supply to the header callback function + * @data_callback: Callback function to call to parse the data entries + * @data_callback_data: Opaque data to supply to the data callback function + * @data: Data to parse + * @data_len: Length of @data + * @data_types: Array of data type strings + * @num_data_types: Number of elements of @data_types + * @fields: Array of field strings + * @num_fields: Number of elements of @fields + * + * Parse data in TLV format and call tlv_parse_data() each time tlv_parse_hdr() + * returns 1. + * + * Return: 0 on success, a negative value on error. + */ +int tlv_parse(hdr_callback hdr_callback, void *hdr_callback_data, + data_callback data_callback, void *data_callback_data, + const __u8 *data, size_t data_len, const char **data_types, + __u64 num_data_types, const char **fields, __u64 num_fields) +{ + __u64 parsed_num_entries, parsed_total_len; + const __u8 *data_ptr = data; + int ret = 0; + + pr_debug("Start parsing data blob, size: %lu\n", data_len); + + while (data_len) { + ret = tlv_parse_hdr(hdr_callback, hdr_callback_data, &data_ptr, + &data_len, &parsed_num_entries, + &parsed_total_len, data_types, + num_data_types); + switch (ret) { + case 0: + /* + * tlv_parse_hdr() already checked that + * parsed_total_len <= data_len. + */ + data_ptr += parsed_total_len; + data_len -= parsed_total_len; + continue; + case 1: + break; + default: + goto out; + } + + ret = tlv_parse_data(data_callback, data_callback_data, + parsed_num_entries, data_ptr, + parsed_total_len, fields, num_fields); + if (ret < 0) + goto out; + + data_ptr += parsed_total_len; + data_len -= parsed_total_len; + } +out: + pr_debug("End of parsing data blob, ret: %d\n", ret); + return ret; +} diff --git a/lib/tlv_parser.h b/lib/tlv_parser.h new file mode 100644 index 000000000000..8fa8127bd13e --- /dev/null +++ b/lib/tlv_parser.h @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Header file of TLV parser. + */ + +#ifndef _LIB_TLV_PARSER_H +#define _LIB_TLV_PARSER_H + +#include <linux/kernel.h> +#include <linux/err.h> +#include <linux/tlv_parser.h> + +#endif /* _LIB_TLV_PARSER_H */

From: Roberto Sassu roberto.sassu@huawei.com

Introduce the Integrity Digest Cache, to collect digests from various sources (called digest lists), and to store them in kernel memory, in a set of hash tables forming a digest cache. Extracted digests can be used as reference values for integrity verification of file data or metadata.

The Integrity Digest Cache aims to be used by IMA and (later) by EVM to verify accessed files. It is not an LSM on its own, and requires IMA (when the feature is enabled) to reserve additional space in the inode security blob and to call digest_cache_do_init() for registering additional LSM hooks.

The additional space in the inode security blob is used for storing the digest_cache_security structure, which contains two digest cache pointers: dig_owner, set if the digest cache was created from that inode; dig_user, set if the digest cache was used for verifying that inode. An inode security blob has both pointers set if digests are extracted from that inode, and the inode itself is verified with another inode. Check and assignment of those pointers are protected respectively with dig_owner_mutex and dig_user_mutex.

The only way for a user of the Integrity Digest Cache to obtain a digest cache is to call digest_cache_get(). The latter first checks if dig_user in the security blob of the passed inode is not NULL and, in that case, immediately returns the pointer after incrementing the digest cache reference count.

If dig_user is NULL, digest_cache_get() calls digest_cache_new(), which determines from which path the digest cache should be retrieved. If the default path (defined in the kernel config, or at run-time) is a file, digest_cache_new() uses it as the final destination. If the default path is a directory, the function attempts to read the security.digest_list xattr and, if found, uses its value as last path component. Lastly, if the xattr is not found or empty, it uses the directory as final destination. A subsequent patch will allow the holders of the returned digest cache to iteratively search a digest in each directory entry.

Finally, digest_cache_new() calls digest_cache_create(), which resolves the inode from the path, and checks if the dig_owner pointer is set. If it is, again, digest_cache_create() immediately returns after incrementing the digest cache reference count. If not, it calls digest_cache_alloc_init() to create a new digest cache. A subsequent patch will initialize it.

A holder of a digest cache can release its reference and consequently decrement the digest cache reference count by calling digest_cache_put(). If the reference count becomes zero, digest_cache_put() also calls digest_cache_free() to free the memory.

Inodes having either dig_owner and dig_user set are also holders of digest caches. Their reference is released when they are evicted from memory, by implementing the inode_free_security LSM hook. The inode_alloc_security LSM hook, instead, initializes the digest_cache_security structure.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- include/linux/digest_cache.h | 30 ++ include/uapi/linux/xattr.h | 3 + security/integrity/Kconfig | 1 + security/integrity/Makefile | 1 + security/integrity/digest_cache/Kconfig | 17 + security/integrity/digest_cache/Makefile | 7 + security/integrity/digest_cache/internal.h | 90 +++++ security/integrity/digest_cache/main.c | 367 +++++++++++++++++++++ security/integrity/ima/ima.h | 1 + security/integrity/ima/ima_main.c | 8 +- 10 files changed, 524 insertions(+), 1 deletion(-) create mode 100644 include/linux/digest_cache.h create mode 100644 security/integrity/digest_cache/Kconfig create mode 100644 security/integrity/digest_cache/Makefile create mode 100644 security/integrity/digest_cache/internal.h create mode 100644 security/integrity/digest_cache/main.c

diff --git a/include/linux/digest_cache.h b/include/linux/digest_cache.h new file mode 100644 index 000000000000..86e6c5a0b896 --- /dev/null +++ b/include/linux/digest_cache.h @@ -0,0 +1,30 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Public API of the Integrity Digest Cache. + */ + +#ifndef _LINUX_DIGEST_CACHE_H +#define _LINUX_DIGEST_CACHE_H + +#include <linux/fs.h> + +#ifdef CONFIG_INTEGRITY_DIGEST_CACHE +struct digest_cache *digest_cache_get(struct dentry *dentry); +void digest_cache_put(struct digest_cache *digest_cache); + +#else +static inline struct digest_cache *digest_cache_get(struct dentry *dentry) +{ + return NULL; +} + +static inline void digest_cache_put(struct digest_cache *digest_cache) +{ +} + +#endif /* CONFIG_INTEGRITY_DIGEST_CACHE */ +#endif /* _LINUX_DIGEST_CACHE_H */ diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h index 9463db2dfa9d..8a58cf4bce65 100644 --- a/include/uapi/linux/xattr.h +++ b/include/uapi/linux/xattr.h @@ -54,6 +54,9 @@ #define XATTR_IMA_SUFFIX "ima" #define XATTR_NAME_IMA XATTR_SECURITY_PREFIX XATTR_IMA_SUFFIX

+#define XATTR_DIGEST_LIST_SUFFIX "digest_list" +#define XATTR_NAME_DIGEST_LIST XATTR_SECURITY_PREFIX XATTR_DIGEST_LIST_SUFFIX + #define XATTR_SELINUX_SUFFIX "selinux" #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX

diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig index 3c45f4f3455f..55b1311a48fa 100644 --- a/security/integrity/Kconfig +++ b/security/integrity/Kconfig @@ -132,5 +132,6 @@ config INTEGRITY_AUDIT

source "security/integrity/ima/Kconfig" source "security/integrity/evm/Kconfig" +source "security/integrity/digest_cache/Kconfig"

endif # if INTEGRITY diff --git a/security/integrity/Makefile b/security/integrity/Makefile index 92b63039c654..0fdabfc6c8ae 100644 --- a/security/integrity/Makefile +++ b/security/integrity/Makefile @@ -21,3 +21,4 @@ integrity-$(CONFIG_LOAD_PPC_KEYS) += platform_certs/efi_parser.o \ # The relative order of the 'ima' and 'evm' LSMs depends on the order below. obj-$(CONFIG_IMA) += ima/ obj-$(CONFIG_EVM) += evm/ +obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache/ diff --git a/security/integrity/digest_cache/Kconfig b/security/integrity/digest_cache/Kconfig new file mode 100644 index 000000000000..5fbec491237b --- /dev/null +++ b/security/integrity/digest_cache/Kconfig @@ -0,0 +1,17 @@ +# SPDX-License-Identifier: GPL-2.0 +config INTEGRITY_DIGEST_CACHE + bool "Integrity Digest Cache" + default n + help + This option enables a cache of reference digests (e.g. of file + data or metadata) to be used by IMA and (later) by EVM, to verify + accessed files. + + Digests can be extracted from RPM headers, or from other sources. + +config DIGEST_LIST_DEFAULT_PATH + string + default "/etc/digest_lists" + help + Default path where the Integrity Digest Cache expects to find digest + lists. diff --git a/security/integrity/digest_cache/Makefile b/security/integrity/digest_cache/Makefile new file mode 100644 index 000000000000..6a3f7cc6e106 --- /dev/null +++ b/security/integrity/digest_cache/Makefile @@ -0,0 +1,7 @@ +# SPDX-License-Identifier: GPL-2.0 +# +# Makefile for building the Integrity Digest Cache. + +obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache.o + +digest_cache-y := main.o diff --git a/security/integrity/digest_cache/internal.h b/security/integrity/digest_cache/internal.h new file mode 100644 index 000000000000..e8a13afaf2fc --- /dev/null +++ b/security/integrity/digest_cache/internal.h @@ -0,0 +1,90 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Internal header of the Integrity Digest Cache. + */ + +#ifndef _DIGEST_CACHE_INTERNAL_H +#define _DIGEST_CACHE_INTERNAL_H + +#include <linux/lsm_hooks.h> +#include <linux/digest_cache.h> + +/** + * struct digest_cache - Digest cache + * @ref_count: Number of references to the digest cache + * @path_str: Path of the digest list the digest cache was created from + * @flags: Control flags + * + * This structure represents a cache of digests extracted from a digest list. + */ +struct digest_cache { + atomic_t ref_count; + char *path_str; + unsigned long flags; +}; + +/** + * struct digest_cache_security - Digest cache pointers in inode security blob + * @dig_owner: Digest cache created from this inode + * @dig_owner_mutex: Protects @dig_owner + * @dig_user: Digest cache requested for this inode + * @dig_user_mutex: Protects @dig_user + * + * This structure contains references to digest caches, protected by their + * respective mutex. + */ +struct digest_cache_security { + struct digest_cache *dig_owner; + struct mutex dig_owner_mutex; + struct digest_cache *dig_user; + struct mutex dig_user_mutex; +}; + +extern loff_t inode_sec_offset; +extern char *default_path_str; + +static inline struct digest_cache_security * +digest_cache_get_security(const struct inode *inode) +{ + if (unlikely(!inode->i_security)) + return NULL; + + return inode->i_security + inode_sec_offset; +} + +static inline struct digest_cache * +digest_cache_ref(struct digest_cache *digest_cache) +{ + int ref_count = atomic_inc_return(&digest_cache->ref_count); + + pr_debug("Ref (+) digest cache %s (ref count: %d)\n", + digest_cache->path_str, ref_count); + return digest_cache; +} + +static inline struct digest_cache * +digest_cache_unref(struct digest_cache *digest_cache) +{ + bool ref_is_zero; + + /* Unreliable ref. count, but cannot decrement before print (UAF). */ + pr_debug("Ref (-) digest cache %s (ref count: %d)\n", + digest_cache->path_str, + atomic_read(&digest_cache->ref_count) - 1); + + ref_is_zero = atomic_dec_and_test(&digest_cache->ref_count); + return (ref_is_zero) ? digest_cache : NULL; +} + +/* main.c */ +struct digest_cache *digest_cache_create(struct dentry *dentry, + struct path *digest_list_path, + char *path_str, char *filename); +int __init digest_cache_do_init(const struct lsm_id *lsm_id, + loff_t inode_offset); + +#endif /* _DIGEST_CACHE_INTERNAL_H */ diff --git a/security/integrity/digest_cache/main.c b/security/integrity/digest_cache/main.c new file mode 100644 index 000000000000..60030df04a4d --- /dev/null +++ b/security/integrity/digest_cache/main.c @@ -0,0 +1,367 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Implement the main code of the Integrity Digest Cache. + */ + +#define pr_fmt(fmt) "digest_cache: "fmt +#include <linux/namei.h> +#include <linux/xattr.h> + +#include "internal.h" + +static int digest_cache_enabled __ro_after_init; +static struct kmem_cache *digest_cache_cache __read_mostly; + +loff_t inode_sec_offset; + +char *default_path_str = CONFIG_DIGEST_LIST_DEFAULT_PATH; + +/** + * digest_cache_alloc_init - Allocate and initialize a new digest cache + * @path_str: Path string of the digest list + * @filename: Digest list file name (can be an empty string) + * + * This function allocates and initializes a new digest cache. + * + * Return: A new digest cache on success, NULL on error. + */ +static struct digest_cache *digest_cache_alloc_init(char *path_str, + char *filename) +{ + struct digest_cache *digest_cache; + + digest_cache = kmem_cache_zalloc(digest_cache_cache, GFP_KERNEL); + if (!digest_cache) + return digest_cache; + + digest_cache->path_str = kasprintf(GFP_KERNEL, "%s%s%s", path_str, + filename[0] ? "/" : "", filename); + if (!digest_cache->path_str) { + kmem_cache_free(digest_cache_cache, digest_cache); + return NULL; + } + + atomic_set(&digest_cache->ref_count, 1); + digest_cache->flags = 0UL; + + pr_debug("New digest cache %s (ref count: %d)\n", + digest_cache->path_str, atomic_read(&digest_cache->ref_count)); + + return digest_cache; +} + +/** + * digest_cache_free - Free all memory occupied by the digest cache + * @digest_cache: Digest cache + * + * This function frees the memory occupied by the digest cache. + */ +static void digest_cache_free(struct digest_cache *digest_cache) +{ + pr_debug("Freed digest cache %s\n", digest_cache->path_str); + kfree(digest_cache->path_str); + kmem_cache_free(digest_cache_cache, digest_cache); +} + +/** + * digest_cache_create - Create a digest cache + * @dentry: Dentry of the inode for which the digest cache will be used + * @digest_list_path: Path structure of the digest list + * @path_str: Path string of the digest list + * @filename: Digest list file name (can be an empty string) + * + * This function first locates, from the passed path, the digest list inode + * from which the digest cache will be created or retrieved (if it already + * exists). + * + * If dig_owner is NULL in the inode security blob, this function creates a + * new digest cache with reference count set to 1 (reference returned), sets + * it to dig_owner and consequently increments again the digest cache reference + * count. + * + * Otherwise, it simply increments the reference count of the existing + * dig_owner, since that reference is returned to the caller. + * + * This function locks dig_owner_mutex to protect against concurrent requests + * to obtain a digest cache from the same inode. + * + * Return: A digest cache on success, NULL on error. + */ +struct digest_cache *digest_cache_create(struct dentry *dentry, + struct path *digest_list_path, + char *path_str, char *filename) +{ + struct path file_path; + struct digest_cache *digest_cache = NULL; + struct digest_cache_security *dig_sec; + struct inode *inode = d_backing_inode(digest_list_path->dentry); + int ret; + + if (S_ISDIR(inode->i_mode) && filename[0]) { + ret = vfs_path_lookup(digest_list_path->dentry, + digest_list_path->mnt, filename, + LOOKUP_FOLLOW, &file_path); + if (ret < 0) { + pr_debug("Cannot find digest list %s/%s\n", path_str, + filename); + return NULL; + } + + digest_list_path = &file_path; + inode = d_backing_inode(file_path.dentry); + + /* No support for nested directories. */ + if (!S_ISREG(inode->i_mode)) { + pr_debug("%s is not a regular file (no support for nested directories)\n", + file_path.dentry->d_name.name); + goto out; + } + } + + /* + * Cannot request a digest cache for the same inode the digest cache + * is populated from. + */ + if (d_backing_inode(dentry) == inode) { + pr_debug("Cannot request a digest cache for %s and create the digest cache from it\n", + dentry->d_name.name); + goto out; + } + + dig_sec = digest_cache_get_security(inode); + if (unlikely(!dig_sec)) + goto out; + + /* Serialize check and assignment of dig_owner. */ + mutex_lock(&dig_sec->dig_owner_mutex); + if (dig_sec->dig_owner) { + /* Increment ref. count for reference returned to the caller. */ + digest_cache = digest_cache_ref(dig_sec->dig_owner); + mutex_unlock(&dig_sec->dig_owner_mutex); + goto out; + } + + /* Ref. count is already 1 for this reference. */ + dig_sec->dig_owner = digest_cache_alloc_init(path_str, filename); + if (!dig_sec->dig_owner) { + mutex_unlock(&dig_sec->dig_owner_mutex); + goto out; + } + + /* Increment ref. count for reference returned to the caller. */ + digest_cache = digest_cache_ref(dig_sec->dig_owner); + mutex_unlock(&dig_sec->dig_owner_mutex); +out: + if (digest_list_path == &file_path) + path_put(&file_path); + + return digest_cache; +} + +/** + * digest_cache_new - Retrieve digest list file name and request digest cache + * @dentry: Dentry of the inode for which the digest cache will be used + * + * This function locates the default path. If it is a file, it directly creates + * a digest cache from it. Otherwise, it reads the digest list file name from + * the security.digest_list xattr and requests the creation of a digest cache + * with that file name. If security.digest_list is empty or not found, this + * function requests the creation of a digest cache on the parent directory. + * + * Return: A digest cache on success, NULL on error. + */ +static struct digest_cache *digest_cache_new(struct dentry *dentry) +{ + char filename[NAME_MAX + 1] = { 0 }; + struct digest_cache *digest_cache = NULL; + struct path default_path; + int ret; + + ret = kern_path(default_path_str, 0, &default_path); + if (ret < 0) { + pr_debug("Cannot find path %s\n", default_path_str); + return NULL; + } + + /* The default path is a file, no need to get xattr. */ + if (S_ISREG(d_backing_inode(default_path.dentry)->i_mode)) { + pr_debug("Default path %s is a file, not reading %s xattr\n", + default_path_str, XATTR_NAME_DIGEST_LIST); + goto create; + } else if (!S_ISDIR(d_backing_inode(default_path.dentry)->i_mode)) { + pr_debug("Default path %s must be either a file or a directory\n", + default_path_str); + goto out; + } + + ret = vfs_getxattr(&nop_mnt_idmap, dentry, XATTR_NAME_DIGEST_LIST, + filename, sizeof(filename) - 1); + if (ret <= 0) { + pr_debug("Digest list file name not found for file %s, using %s\n", + dentry->d_name.name, default_path_str); + if (ret && ret != -ENODATA) + goto out; + + goto create; + } + + if (strchr(filename, '/')) { + pr_debug("%s xattr should contain only a file name, got: %s\n", + XATTR_NAME_DIGEST_LIST, filename); + goto out; + } + + pr_debug("Found %s xattr in %s, default path: %s, digest list: %s\n", + XATTR_NAME_DIGEST_LIST, dentry->d_name.name, default_path_str, + filename); +create: + digest_cache = digest_cache_create(dentry, &default_path, + default_path_str, filename); +out: + path_put(&default_path); + return digest_cache; +} + +/** + * digest_cache_get - Get a digest cache for a given inode + * @dentry: Dentry of the inode for which the digest cache will be used + * + * This function tries to find a digest cache from the inode security blob of + * the passed dentry (dig_user field). If a digest cache was not found, it calls + * digest_cache_new() to create a new one. In both cases, it increments the + * digest cache reference count before returning the reference to the caller. + * + * The caller is responsible to call digest_cache_put() to release the digest + * cache reference returned. + * + * This function locks dig_user_mutex to protect against concurrent requests + * to obtain a digest cache for the same inode. + * + * Return: A digest cache on success, NULL otherwise. + */ +struct digest_cache *digest_cache_get(struct dentry *dentry) +{ + struct digest_cache_security *dig_sec; + struct digest_cache *digest_cache = NULL; + struct inode *inode = d_backing_inode(dentry); + + if (!digest_cache_enabled) + return NULL; + + dig_sec = digest_cache_get_security(inode); + if (unlikely(!dig_sec)) + return NULL; + + /* Serialize accesses to inode for which the digest cache is used. */ + mutex_lock(&dig_sec->dig_user_mutex); + if (!dig_sec->dig_user) + /* Consume extra reference from digest_cache_create(). */ + dig_sec->dig_user = digest_cache_new(dentry); + + if (dig_sec->dig_user) + /* Increment ref. count for reference returned to the caller. */ + digest_cache = digest_cache_ref(dig_sec->dig_user); + + mutex_unlock(&dig_sec->dig_user_mutex); + + return digest_cache; +} +EXPORT_SYMBOL_GPL(digest_cache_get); + +/** + * digest_cache_put - Release a digest cache reference + * @digest_cache: Digest cache + * + * This function decrements the reference count of the digest cache passed as + * argument. If the reference count reaches zero, it calls digest_cache_free() + * to free the digest cache. + */ +void digest_cache_put(struct digest_cache *digest_cache) +{ + struct digest_cache *to_free; + + to_free = digest_cache_unref(digest_cache); + if (!to_free) + return; + + digest_cache_free(to_free); +} +EXPORT_SYMBOL_GPL(digest_cache_put); + +/** + * digest_cache_inode_alloc_security - Initialize inode security blob + * @inode: Inode for which the security blob is initialized + * + * This function initializes the digest_cache_security structure, directly + * stored in the inode security blob. + * + * Return: Zero. + */ +static int digest_cache_inode_alloc_security(struct inode *inode) +{ + struct digest_cache_security *dig_sec; + + /* The inode security blob is always allocated here. */ + dig_sec = digest_cache_get_security(inode); + mutex_init(&dig_sec->dig_owner_mutex); + mutex_init(&dig_sec->dig_user_mutex); + return 0; +} + +/** + * digest_cache_inode_free_security - Release the digest cache references + * @inode: Inode for which the digest cache references are released + * + * Since the inode is being evicted, this function releases the non-needed + * references to the digest caches stored in the digest_cache_security + * structure. + */ +static void digest_cache_inode_free_security(struct inode *inode) +{ + struct digest_cache_security *dig_sec; + + dig_sec = digest_cache_get_security(inode); + if (!dig_sec) + return; + + mutex_destroy(&dig_sec->dig_owner_mutex); + mutex_destroy(&dig_sec->dig_user_mutex); + if (dig_sec->dig_owner) + digest_cache_put(dig_sec->dig_owner); + if (dig_sec->dig_user) + digest_cache_put(dig_sec->dig_user); +} + +static struct security_hook_list digest_cache_hooks[] __ro_after_init = { + LSM_HOOK_INIT(inode_alloc_security, digest_cache_inode_alloc_security), + LSM_HOOK_INIT(inode_free_security, digest_cache_inode_free_security), +}; + +/** + * digest_cache_do_init - Initialize the Integrity Digest Cache + * @lsm_id: ID of LSM registering the LSM hooks + * @inode_offset: Offset in the inode security blob + * + * Initialize the Integrity Digest Cache, by instantiating a cache for the + * digest_cache structure and by registering the LSM hooks as part of the + * calling LSM. + */ +int __init digest_cache_do_init(const struct lsm_id *lsm_id, + loff_t inode_offset) +{ + inode_sec_offset = inode_offset; + + digest_cache_cache = kmem_cache_create("digest_cache_cache", + sizeof(struct digest_cache), + 0, SLAB_PANIC, NULL); + + security_add_hooks(digest_cache_hooks, ARRAY_SIZE(digest_cache_hooks), + lsm_id); + + digest_cache_enabled = 1; + return 0; +} diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index c51e24d24d1e..ad5c95cf22ac 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -23,6 +23,7 @@ #include <crypto/hash_info.h>

#include "../integrity.h" +#include "../digest_cache/internal.h"

enum ima_show_type { IMA_SHOW_BINARY, IMA_SHOW_BINARY_NO_FIELD_LEN, IMA_SHOW_BINARY_OLD_STRING_FMT, IMA_SHOW_ASCII }; diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index f04f43af651c..7cbd78ca3be5 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -1206,11 +1206,17 @@ static int __init init_ima_lsm(void) ima_iintcache_init(); security_add_hooks(ima_hooks, ARRAY_SIZE(ima_hooks), &ima_lsmid); init_ima_appraise_lsm(&ima_lsmid); + if (IS_ENABLED(CONFIG_INTEGRITY_DIGEST_CACHE)) + digest_cache_do_init(&ima_lsmid, ima_blob_sizes.lbs_inode + + sizeof(struct ima_iint_cache *)); return 0; }

struct lsm_blob_sizes ima_blob_sizes __ro_after_init = { - .lbs_inode = sizeof(struct ima_iint_cache *), + .lbs_inode = sizeof(struct ima_iint_cache *) +#ifdef CONFIG_INTEGRITY_DIGEST_CACHE + + sizeof(struct digest_cache_security) +#endif };

DEFINE_LSM(ima) = {

From: Roberto Sassu roberto.sassu@huawei.com

Create the digest_cache directory in <securityfs>/integrity, and add the default_path file, to let root change/read the default path (file or directory) from where digest lists are looked up.

An RW semaphore prevents the default path from changing while digest_list_new() and read_default_path() are executed, so that those read a stable value. Multiple digest_list_new() and read_default_path() calls, instead, can be done in parallel, since they are the readers.

Changing the default path does not affect digest caches created with the old path.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- security/integrity/digest_cache/Kconfig | 4 + security/integrity/digest_cache/Makefile | 2 +- security/integrity/digest_cache/internal.h | 4 + security/integrity/digest_cache/main.c | 10 +- security/integrity/digest_cache/secfs.c | 104 +++++++++++++++++++++ security/integrity/ima/ima_fs.c | 6 ++ 6 files changed, 128 insertions(+), 2 deletions(-) create mode 100644 security/integrity/digest_cache/secfs.c

diff --git a/security/integrity/digest_cache/Kconfig b/security/integrity/digest_cache/Kconfig index 5fbec491237b..6e61089acbe2 100644 --- a/security/integrity/digest_cache/Kconfig +++ b/security/integrity/digest_cache/Kconfig @@ -15,3 +15,7 @@ config DIGEST_LIST_DEFAULT_PATH help Default path where the Integrity Digest Cache expects to find digest lists. + + It can be changed at run-time, by writing the new path to the + securityfs interface. Digest caches created with the old path are + not affected by the change. diff --git a/security/integrity/digest_cache/Makefile b/security/integrity/digest_cache/Makefile index 6a3f7cc6e106..c351186d4e1e 100644 --- a/security/integrity/digest_cache/Makefile +++ b/security/integrity/digest_cache/Makefile @@ -4,4 +4,4 @@

obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache.o

-digest_cache-y := main.o +digest_cache-y := main.o secfs.o diff --git a/security/integrity/digest_cache/internal.h b/security/integrity/digest_cache/internal.h index 54e118a2ef79..2fcfa9b4cf13 100644 --- a/security/integrity/digest_cache/internal.h +++ b/security/integrity/digest_cache/internal.h @@ -53,6 +53,7 @@ struct digest_cache_security {

extern loff_t inode_sec_offset; extern char *default_path_str; +extern struct rw_semaphore default_path_sem;

static inline struct digest_cache_security * digest_cache_get_security(const struct inode *inode) @@ -96,4 +97,7 @@ struct digest_cache *digest_cache_init(struct dentry *dentry, int __init digest_cache_do_init(const struct lsm_id *lsm_id, loff_t inode_offset);

+/* secfs.c */ +int __init digest_cache_secfs_init(struct dentry *dir); + #endif /* _DIGEST_CACHE_INTERNAL_H */ diff --git a/security/integrity/digest_cache/main.c b/security/integrity/digest_cache/main.c index 188f1dcc880e..0e25f573166a 100644 --- a/security/integrity/digest_cache/main.c +++ b/security/integrity/digest_cache/main.c @@ -20,6 +20,9 @@ loff_t inode_sec_offset;

char *default_path_str = CONFIG_DIGEST_LIST_DEFAULT_PATH;

+/* Protects default_path_str. */ +struct rw_semaphore default_path_sem; + /** * digest_cache_alloc_init - Allocate and initialize a new digest cache * @path_str: Path string of the digest list @@ -305,9 +308,12 @@ struct digest_cache *digest_cache_get(struct dentry *dentry)

/* Serialize accesses to inode for which the digest cache is used. */ mutex_lock(&dig_sec->dig_user_mutex); - if (!dig_sec->dig_user) + if (!dig_sec->dig_user) { + down_read(&default_path_sem); /* Consume extra reference from digest_cache_create(). */ dig_sec->dig_user = digest_cache_new(dentry); + up_read(&default_path_sem); + }

if (dig_sec->dig_user) /* Increment ref. count for reference returned to the caller. */ @@ -404,6 +410,8 @@ static struct security_hook_list digest_cache_hooks[] __ro_after_init = { int __init digest_cache_do_init(const struct lsm_id *lsm_id, loff_t inode_offset) { + init_rwsem(&default_path_sem); + inode_sec_offset = inode_offset;

digest_cache_cache = kmem_cache_create("digest_cache_cache", diff --git a/security/integrity/digest_cache/secfs.c b/security/integrity/digest_cache/secfs.c new file mode 100644 index 000000000000..3267b2a83430 --- /dev/null +++ b/security/integrity/digest_cache/secfs.c @@ -0,0 +1,104 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Implement the securityfs interface of the Integrity Digest Cache. + */ + +#define pr_fmt(fmt) "digest_cache: "fmt +#include <linux/security.h> + +#include "internal.h" + +static struct dentry *digest_cache_dir; +static struct dentry *default_path_dentry; + +/** + * write_default_path - Write default path + * @file: File descriptor of the securityfs file + * @buf: User space buffer + * @datalen: Amount of data to write + * @ppos: Current position in the file + * + * This function sets the new default path where digest lists can be found. + * Can be either a regular file or a directory. + * + * Return: Length of path written on success, a POSIX error code otherwise. + */ +static ssize_t write_default_path(struct file *file, const char __user *buf, + size_t datalen, loff_t *ppos) +{ + char *new_default_path_str; + + new_default_path_str = memdup_user_nul(buf, datalen); + if (IS_ERR(new_default_path_str)) + return PTR_ERR(new_default_path_str); + + down_write(&default_path_sem); + kfree_const(default_path_str); + default_path_str = new_default_path_str; + up_write(&default_path_sem); + return datalen; +} + +/** + * read_default_path - Read default path + * @file: File descriptor of the securityfs file + * @buf: User space buffer + * @datalen: Amount of data to read + * @ppos: Current position in the file + * + * This function returns the current default path where digest lists can be + * found. Can be either a regular file or a directory. + * + * Return: Length of path read on success, a POSIX error code otherwise. + */ +static ssize_t read_default_path(struct file *file, char __user *buf, + size_t datalen, loff_t *ppos) +{ + int ret; + + down_read(&default_path_sem); + ret = simple_read_from_buffer(buf, datalen, ppos, default_path_str, + strlen(default_path_str) + 1); + up_read(&default_path_sem); + return ret; +} + +static const struct file_operations default_path_ops = { + .open = generic_file_open, + .write = write_default_path, + .read = read_default_path, + .llseek = generic_file_llseek, +}; + +/** + * digest_cache_secfs_init - Initialize the securityfs interface + * @dir: Directory entry provided by the calling LSM + * + * This function initialize the securityfs interfaces, for configuration + * by user space. + * + * Initialize 'default_path', allowing user space to change the default + * directory where digest lists are searched. + * + * Return: Zero on success, a POSIX error code otherwise. + */ +int __init digest_cache_secfs_init(struct dentry *dir) +{ + digest_cache_dir = securityfs_create_dir("digest_cache", dir); + if (IS_ERR(digest_cache_dir)) + return PTR_ERR(digest_cache_dir); + + default_path_dentry = securityfs_create_file("default_path", 0660, + digest_cache_dir, NULL, + &default_path_ops); + if (IS_ERR(default_path_dentry)) { + securityfs_remove(digest_cache_dir); + return PTR_ERR(default_path_dentry); + } + + return 0; +} diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c index e4a79a9b2d58..be9e374e2cef 100644 --- a/security/integrity/ima/ima_fs.c +++ b/security/integrity/ima/ima_fs.c @@ -614,6 +614,12 @@ int __init ima_fs_init(void) goto out; }

+ if (IS_ENABLED(CONFIG_INTEGRITY_DIGEST_CACHE)) { + ret = digest_cache_secfs_init(integrity_dir); + if (ret < 0) + goto out; + } + return 0; out: securityfs_remove(ima_policy);

From: Roberto Sassu roberto.sassu@huawei.com

Introduce digest_cache_populate() to populate the digest cache from a digest list. Call it from digest_cache_init() if the inode is a regular file.

It opens the file and then schedules a work to read the content (with new file type READING_DIGEST_LIST). Scheduling a work solves the problem of kernel_read_file() returning -EINTR.

Once the work is done, this function calls digest_cache_strip_modsig() to strip a module-style appended signature, if present, and finally calls digest_cache_parse_digest_list() to parse the data.

The latter function, which at the moment does nothing, will be completed with calls to parsing functions selected from the digest list file name. It expects digest lists file names to be in the format:

[<seq num>-]<digest list format>-<digest list name>

<seq-num>- is an optional prefix to impose in which order digest lists in a directory should be parsed.

Failing to populate a digest cache causes it to be marked as invalid and to not be returned by digest_cache_init(). Dig_owner however is kept, to avoid an excessive number of retries, which would probably not succeed either.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- include/linux/kernel_read_file.h | 1 + security/integrity/digest_cache/Makefile | 2 +- security/integrity/digest_cache/internal.h | 24 ++++ security/integrity/digest_cache/main.c | 16 +++ security/integrity/digest_cache/modsig.c | 66 ++++++++++ security/integrity/digest_cache/populate.c | 142 +++++++++++++++++++++ 6 files changed, 250 insertions(+), 1 deletion(-) create mode 100644 security/integrity/digest_cache/modsig.c create mode 100644 security/integrity/digest_cache/populate.c

diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h index 90451e2e12bd..85f602e49e2f 100644 --- a/include/linux/kernel_read_file.h +++ b/include/linux/kernel_read_file.h @@ -14,6 +14,7 @@ id(KEXEC_INITRAMFS, kexec-initramfs) \ id(POLICY, security-policy) \ id(X509_CERTIFICATE, x509-certificate) \ + id(DIGEST_LIST, digest-list) \ id(MAX_ID, )

#define __fid_enumify(ENUM, dummy) READING_ ## ENUM, diff --git a/security/integrity/digest_cache/Makefile b/security/integrity/digest_cache/Makefile index 0092c913979d..1b91f9fba51c 100644 --- a/security/integrity/digest_cache/Makefile +++ b/security/integrity/digest_cache/Makefile @@ -4,4 +4,4 @@

obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache.o

-digest_cache-y := main.o secfs.o htable.o +digest_cache-y := main.o secfs.o htable.o populate.o modsig.o diff --git a/security/integrity/digest_cache/internal.h b/security/integrity/digest_cache/internal.h index f4b146a1bbaf..f8ec51405bae 100644 --- a/security/integrity/digest_cache/internal.h +++ b/security/integrity/digest_cache/internal.h @@ -18,6 +18,23 @@ #define INIT_STARTED 1 /* Digest cache init started. */ #define INVALID 2 /* Digest cache marked as invalid. */

+/** + * struct read_work - Structure to schedule reading a digest list + * @work: Work structure + * @file: File descriptor of the digest list to read + * @data: Digest list data (updated) + * @ret: Return value from kernel_read_file() (updated) + * + * This structure contains the necessary information to schedule reading a + * digest list. + */ +struct read_work { + struct work_struct work; + struct file *file; + void *data; + int ret; +}; + /** * struct digest_cache_entry - Entry of a digest cache hash table * @hnext: Pointer to the next element in the collision list @@ -143,4 +160,11 @@ int digest_cache_htable_lookup(struct dentry *dentry, enum hash_algo algo); void digest_cache_htable_free(struct digest_cache *digest_cache);

+/* populate.c */ +int digest_cache_populate(struct digest_cache *digest_cache, + struct path *digest_list_path); + +/* modsig.c */ +size_t digest_cache_strip_modsig(__u8 *data, size_t data_len); + #endif /* _DIGEST_CACHE_INTERNAL_H */ diff --git a/security/integrity/digest_cache/main.c b/security/integrity/digest_cache/main.c index a74fc1183332..6878ebe5b779 100644 --- a/security/integrity/digest_cache/main.c +++ b/security/integrity/digest_cache/main.c @@ -258,6 +258,9 @@ static struct digest_cache *digest_cache_new(struct dentry *dentry) struct digest_cache *digest_cache_init(struct dentry *dentry, struct digest_cache *digest_cache) { + struct inode *inode; + int ret; + /* Wait for digest cache initialization. */ if (test_and_set_bit(INIT_STARTED, &digest_cache->flags)) { wait_on_bit(&digest_cache->flags, INIT_IN_PROGRESS, @@ -265,6 +268,19 @@ struct digest_cache *digest_cache_init(struct dentry *dentry, goto out; }

+ inode = d_backing_inode(digest_cache->digest_list_path.dentry); + + if (S_ISREG(inode->i_mode)) { + ret = digest_cache_populate(digest_cache, + &digest_cache->digest_list_path); + if (ret < 0) { + pr_debug("Failed to populate digest cache %s ret: %d (keep digest cache)\n", + digest_cache->path_str, ret); + /* Prevent usage of partially-populated digest cache. */ + set_bit(INVALID, &digest_cache->flags); + } + } + path_put(&digest_cache->digest_list_path); /* Notify initialization complete. */ clear_and_wake_up_bit(INIT_IN_PROGRESS, &digest_cache->flags); diff --git a/security/integrity/digest_cache/modsig.c b/security/integrity/digest_cache/modsig.c new file mode 100644 index 000000000000..fa512c43a556 --- /dev/null +++ b/security/integrity/digest_cache/modsig.c @@ -0,0 +1,66 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. + * Copyright (C) 2019 IBM Corporation + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Strip module-style appended signatures. + */ + +#define pr_fmt(fmt) "digest_cache: "fmt +#include <linux/module.h> +#include <linux/module_signature.h> + +#include "internal.h" + +/** + * digest_cache_strip_modsig - Strip module-style appended sig from digest list + * @data: Data to parse + * @data_len: Length of @data + * + * This function strips the module-style appended signature from a digest list, + * if present. + * + * Return: Size of stripped data on success, original size otherwise. + */ +size_t digest_cache_strip_modsig(__u8 *data, size_t data_len) +{ + const size_t marker_len = strlen(MODULE_SIG_STRING); + const struct module_signature *sig; + size_t parsed_data_len = data_len; + size_t sig_len; + const void *p; + + /* From ima_modsig.c */ + if (data_len <= marker_len + sizeof(*sig)) + return data_len; + + p = data + parsed_data_len - marker_len; + if (memcmp(p, MODULE_SIG_STRING, marker_len)) + return data_len; + + parsed_data_len -= marker_len; + sig = (const struct module_signature *)(p - sizeof(*sig)); + + /* From module_signature.c */ + if (be32_to_cpu(sig->sig_len) >= parsed_data_len - sizeof(*sig)) + return data_len; + + /* Unlike for module signatures, accept all signature types. */ + if (sig->algo != 0 || + sig->hash != 0 || + sig->signer_len != 0 || + sig->key_id_len != 0 || + sig->__pad[0] != 0 || + sig->__pad[1] != 0 || + sig->__pad[2] != 0) { + pr_debug("Signature info has unexpected non-zero params\n"); + return data_len; + } + + sig_len = be32_to_cpu(sig->sig_len); + parsed_data_len -= sig_len + sizeof(*sig); + return parsed_data_len; +} diff --git a/security/integrity/digest_cache/populate.c b/security/integrity/digest_cache/populate.c new file mode 100644 index 000000000000..c68c76971380 --- /dev/null +++ b/security/integrity/digest_cache/populate.c @@ -0,0 +1,142 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Implement the code to populate a digest cache. + */ + +#define pr_fmt(fmt) "digest_cache: "fmt +#include <linux/init_task.h> +#include <linux/vmalloc.h> +#include <linux/kernel_read_file.h> + +#include "internal.h" + +/** + * digest_cache_parse_digest_list - Parse a digest list + * @digest_cache: Digest cache + * @path_str: Path string of the digest list + * @data: Data to parse + * @data_len: Length of @data + * + * This function selects a parser for a digest list depending on its file name, + * and calls the appropriate parsing function. It expects the file name to be + * in the format: [<seq num>-]<format>-<digest list name>. <seq num>- is + * optional. + * + * Return: Zero on success, a POSIX error code otherwise. + */ +static int digest_cache_parse_digest_list(struct digest_cache *digest_cache, + char *path_str, void *data, + size_t data_len) +{ + char *filename, *format, *next_sep; + int ret = -EINVAL; + + filename = strrchr(path_str, '/'); + if (!filename) + return ret; + + filename++; + format = filename; + + /* + * Since we expect that all files start with a digest list format, this + * check is reliable to detect <seq num>. + */ + if (filename[0] >= '0' && filename[0] <= '9') { + format = strchr(filename, '-'); + if (!format) + return ret; + + format++; + } + + next_sep = strchr(format, '-'); + if (!next_sep) + return ret; + + pr_debug("Parsing %s, format: %.*s, size: %ld\n", path_str, + (int)(next_sep - format), format, data_len); + + return ret; +} + +/** + * digest_cache_read_digest_list - Read a digest list + * @work: Work structure + * + * This function is invoked by schedule_work() to read a digest list. + * + * It does not return a value, but stores the result in the passed structure. + */ +static void digest_cache_read_digest_list(struct work_struct *work) +{ + struct read_work *w = container_of(work, struct read_work, work); + + w->ret = kernel_read_file(w->file, 0, &w->data, INT_MAX, NULL, + READING_DIGEST_LIST); +} + +/** + * digest_cache_populate - Populate a digest cache from a digest list + * @digest_cache: Digest cache + * @digest_list_path: Path structure of the digest list + * + * This function opens the digest list for reading it. Then, it schedules a + * work to read the digest list and, once the work is done, it calls + * digest_cache_strip_modsig() to strip a module-style appended signature and + * digest_cache_parse_digest_list() for extracting and adding digests to the + * digest cache. + * + * Return: Zero on success, a POSIX error code otherwise. + */ +int digest_cache_populate(struct digest_cache *digest_cache, + struct path *digest_list_path) +{ + struct file *file; + void *data; + size_t data_len; + struct read_work w; + int ret; + + file = dentry_open(digest_list_path, O_RDONLY, &init_cred); + if (IS_ERR(file)) { + pr_debug("Unable to open digest list %s, ret: %ld\n", + digest_cache->path_str, PTR_ERR(file)); + return PTR_ERR(file); + } + + w.data = NULL; + w.file = file; + INIT_WORK_ONSTACK(&w.work, digest_cache_read_digest_list); + + schedule_work(&w.work); + flush_work(&w.work); + destroy_work_on_stack(&w.work); + fput(file); + + ret = w.ret; + data = w.data; + + if (ret < 0) { + pr_debug("Unable to read digest list %s, ret: %d\n", + digest_cache->path_str, ret); + return ret; + } + + data_len = digest_cache_strip_modsig(data, ret); + + /* Digest list parsers initialize the hash table and add the digests. */ + ret = digest_cache_parse_digest_list(digest_cache, + digest_cache->path_str, data, + data_len); + if (ret < 0) + pr_debug("Error parsing digest list %s, ret: %d\n", + digest_cache->path_str, ret); + + vfree(data); + return ret; +}

From: Roberto Sassu roberto.sassu@huawei.com

Implement a simple parser of RPM headers, that extracts the digest and the algorithm of the packaged files from the RPMTAG_FILEDIGESTS and RPMTAG_FILEDIGESTALGO section, and adds them to the digest cache.

The rpm digest list parser has been verified with Frama-C (https://frama-c.com/).

The analysis has been done on this file:

https://github.com/robertosassu/rpm-formal/blob/main/validate_rpm.c

Here is the result of the analysis:

[eva:summary] ====== ANALYSIS SUMMARY ====== --------------------------------------------------------------------------- 7 functions analyzed (out of 7): 100% coverage. In these functions, 227 statements reached (out of 242): 93% coverage. --------------------------------------------------------------------------- No errors or warnings raised during the analysis. --------------------------------------------------------------------------- 0 alarms generated by the analysis. --------------------------------------------------------------------------- Evaluation of the logical properties reached by the analysis: Assertions 6 valid 0 unknown 0 invalid 6 total Preconditions 29 valid 0 unknown 0 invalid 29 total 100% of the logical properties reached have been proven. ---------------------------------------------------------------------------

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- security/integrity/digest_cache/Makefile | 1 + .../integrity/digest_cache/parsers/parsers.h | 2 + security/integrity/digest_cache/parsers/rpm.c | 220 ++++++++++++++++++ security/integrity/digest_cache/populate.c | 2 + 4 files changed, 225 insertions(+) create mode 100644 security/integrity/digest_cache/parsers/rpm.c

diff --git a/security/integrity/digest_cache/Makefile b/security/integrity/digest_cache/Makefile index 5cf75c961e26..681276a4c756 100644 --- a/security/integrity/digest_cache/Makefile +++ b/security/integrity/digest_cache/Makefile @@ -7,3 +7,4 @@ obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache.o digest_cache-y := main.o secfs.o htable.o populate.o modsig.o

digest_cache-y += parsers/tlv.o +digest_cache-y += parsers/rpm.o diff --git a/security/integrity/digest_cache/parsers/parsers.h b/security/integrity/digest_cache/parsers/parsers.h index 1bbae426ab9f..3f00d29ed92a 100644 --- a/security/integrity/digest_cache/parsers/parsers.h +++ b/security/integrity/digest_cache/parsers/parsers.h @@ -11,3 +11,5 @@

int digest_list_parse_tlv(struct digest_cache *digest_cache, const u8 *data, size_t data_len); +int digest_list_parse_rpm(struct digest_cache *digest_cache, const u8 *data, + size_t data_len); diff --git a/security/integrity/digest_cache/parsers/rpm.c b/security/integrity/digest_cache/parsers/rpm.c new file mode 100644 index 000000000000..6949d12707b8 --- /dev/null +++ b/security/integrity/digest_cache/parsers/rpm.c @@ -0,0 +1,220 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2017-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Parse an rpm digest list (RPM package header). + */ + +#define pr_fmt(fmt) "digest_cache RPM PARSER: "fmt +#include <linux/module.h> + +#include "parsers.h" + +#define RPMTAG_FILEDIGESTS 1035 +#define RPMTAG_FILEDIGESTALGO 5011 + +#define RPM_INT32_TYPE 4 +#define RPM_STRING_ARRAY_TYPE 8 + +struct rpm_hdr { + u32 magic; + u32 reserved; + u32 tags; + u32 datasize; +}; + +struct rpm_entryinfo { + s32 tag; + u32 type; + s32 offset; + u32 count; +}; + +enum pgp_algos { + DIGEST_ALGO_MD5 = 1, + DIGEST_ALGO_SHA1 = 2, + DIGEST_ALGO_RMD160 = 3, + /* 4, 5, 6, and 7 are reserved. */ + DIGEST_ALGO_SHA256 = 8, + DIGEST_ALGO_SHA384 = 9, + DIGEST_ALGO_SHA512 = 10, + DIGEST_ALGO_SHA224 = 11, +}; + +static const enum hash_algo pgp_algo_mapping[DIGEST_ALGO_SHA224 + 1] = { + [DIGEST_ALGO_MD5] = HASH_ALGO_MD5, + [DIGEST_ALGO_SHA1] = HASH_ALGO_SHA1, + [DIGEST_ALGO_RMD160] = HASH_ALGO_RIPE_MD_160, + [4] = HASH_ALGO__LAST, + [5] = HASH_ALGO__LAST, + [6] = HASH_ALGO__LAST, + [7] = HASH_ALGO__LAST, + [DIGEST_ALGO_SHA256] = HASH_ALGO_SHA256, + [DIGEST_ALGO_SHA384] = HASH_ALGO_SHA384, + [DIGEST_ALGO_SHA512] = HASH_ALGO_SHA512, + [DIGEST_ALGO_SHA224] = HASH_ALGO_SHA224, +}; + +/** + * digest_list_parse_rpm - Parse an rpm digest list + * @digest_cache: Digest cache + * @data: Data to parse + * @data_len: Length of @data + * + * This function parses an rpm digest list. + * + * Return: Zero on success, a POSIX error code otherwise. + */ +int digest_list_parse_rpm(struct digest_cache *digest_cache, const u8 *data, + size_t data_len) +{ + const unsigned char rpm_header_magic[8] = { + 0x8e, 0xad, 0xe8, 0x01, 0x00, 0x00, 0x00, 0x00 + }; + const struct rpm_hdr *hdr; + const struct rpm_entryinfo *entry; + u32 tags, max_tags, datasize; + u32 digests_count, max_digests_count; + u32 digests_offset, algo_offset; + u32 digest_len, pkg_pgp_algo, i; + bool algo_offset_set = false, digests_offset_set = false; + enum hash_algo pkg_kernel_algo = HASH_ALGO_MD5; + u8 rpm_digest[SHA512_DIGEST_SIZE]; + int ret; + + if (data_len < sizeof(*hdr)) { + pr_debug("Not enough data for RPM header, current %ld, expected: %ld\n", + data_len, sizeof(*hdr)); + return -EINVAL; + } + + if (memcmp(data, rpm_header_magic, sizeof(rpm_header_magic))) { + pr_debug("RPM header magic mismatch\n"); + return -EINVAL; + } + + hdr = (const struct rpm_hdr *)data; + data += sizeof(*hdr); + data_len -= sizeof(*hdr); + + tags = __be32_to_cpu(hdr->tags); + max_tags = data_len / sizeof(*entry); + + /* Possibly lower limit on tags loop. */ + if (tags > max_tags) + return -EINVAL; + + datasize = __be32_to_cpu(hdr->datasize); + if (datasize != data_len - tags * sizeof(*entry)) + return -EINVAL; + + pr_debug("Scanning %d RPM header sections\n", tags); + for (i = 0; i < tags; i++) { + entry = (const struct rpm_entryinfo *)data; + data += sizeof(*entry); + data_len -= sizeof(*entry); + + switch (__be32_to_cpu(entry->tag)) { + case RPMTAG_FILEDIGESTS: + if (__be32_to_cpu(entry->type) != RPM_STRING_ARRAY_TYPE) + return -EINVAL; + + digests_offset = __be32_to_cpu(entry->offset); + digests_count = __be32_to_cpu(entry->count); + digests_offset_set = true; + + pr_debug("Found RPMTAG_FILEDIGESTS at offset %u, count: %u\n", + digests_offset, digests_count); + break; + case RPMTAG_FILEDIGESTALGO: + if (__be32_to_cpu(entry->type) != RPM_INT32_TYPE) + return -EINVAL; + + algo_offset = __be32_to_cpu(entry->offset); + algo_offset_set = true; + + pr_debug("Found RPMTAG_FILEDIGESTALGO at offset %u\n", + algo_offset); + break; + default: + break; + } + } + + if (!digests_offset_set) + return 0; + + if (algo_offset_set) { + if (algo_offset >= data_len) + return -EINVAL; + + if (data_len - algo_offset < sizeof(u32)) + return -EINVAL; + + pkg_pgp_algo = *(u32 *)&data[algo_offset]; + pkg_pgp_algo = __be32_to_cpu(pkg_pgp_algo); + if (pkg_pgp_algo > DIGEST_ALGO_SHA224) { + pr_debug("Unknown PGP algo %d\n", pkg_pgp_algo); + return -EINVAL; + } + + pkg_kernel_algo = pgp_algo_mapping[pkg_pgp_algo]; + if (pkg_kernel_algo >= HASH_ALGO__LAST) { + pr_debug("Unknown mapping for PGP algo %d\n", + pkg_pgp_algo); + return -EINVAL; + } + + pr_debug("Found mapping for PGP algo %d: %s\n", pkg_pgp_algo, + hash_algo_name[pkg_kernel_algo]); + } + + digest_len = hash_digest_size[pkg_kernel_algo]; + + if (digests_offset > data_len) + return -EINVAL; + + /* Worst case, every digest is a \0. */ + max_digests_count = data_len - digests_offset; + + /* Possibly lower limit on digests_count loop. */ + if (digests_count > max_digests_count) + return -EINVAL; + + ret = digest_cache_htable_init(digest_cache, digests_count, + pkg_kernel_algo); + if (ret < 0) + return ret; + + for (i = 0; i < digests_count; i++) { + if (digests_offset == data_len) + return -EINVAL; + + if (!data[digests_offset]) { + digests_offset++; + continue; + } + + if (data_len - digests_offset < digest_len * 2 + 1) + return -EINVAL; + + ret = hex2bin(rpm_digest, (const char *)&data[digests_offset], + digest_len); + if (ret < 0) { + pr_debug("Invalid hex format for digest %s\n", + &data[digests_offset]); + return ret; + } + + ret = digest_cache_htable_add(digest_cache, rpm_digest, + pkg_kernel_algo); + if (ret < 0) + return ret; + + digests_offset += digest_len * 2 + 1; + } + + return ret; +} diff --git a/security/integrity/digest_cache/populate.c b/security/integrity/digest_cache/populate.c index c118658f547a..1c68d957bf1d 100644 --- a/security/integrity/digest_cache/populate.c +++ b/security/integrity/digest_cache/populate.c @@ -64,6 +64,8 @@ static int digest_cache_parse_digest_list(struct digest_cache *digest_cache,

if (!strncmp(format, "tlv-", 4)) ret = digest_list_parse_tlv(digest_cache, data, data_len); + else if (!strncmp(format, "rpm-", 4)) + ret = digest_list_parse_rpm(digest_cache, data, data_len);

return ret; }

From: Roberto Sassu roberto.sassu@huawei.com

In the environments where xattrs are not available (e.g. in the initial ram disk), the Integrity Digest Cache cannot precisely determine which digest list in a directory contains the desired reference digest. However, although slower, it would be desirable to search the digest in all digest lists of that directory.

This done in three steps. First, a directory digest cache is created like the other digest caches. The only differences are that this digest cache has the IS_DIR bit set, to distinguish it from those created from regular files and, consequently, that it stores a list of directory entries file names instead of hash tables for digests.

Second, the directory digest cache is populated with current directory entries, by calling digest_cache_dir_add_entries().

Finally, digest_cache_dir_lookup_digest() is called with the directory digest cache passed as argument, to iteratively search on each digest cache for each directory entry.

The function first calls digest_cache_dir_create() to create/obtain the current directory digest cache for the directory. If this function returns a different one than the one passed, it means that the directory was modified between the get and lookup operations, and it uses the new one.

Then, digest_cache_dir_lookup_digest() starts the lookup and iteratively searches the passed digest in each directory entry. If there is no digest cache associated to the current directory entry, digest_cache_dir_lookup_digest() creates/obtains one by calling digest_cache_create(). It also keeps a digest cache reference, so that it is available for next searches.

The iteration stops when the digest is found. Since the digest cache containing the digest has been found, digest_cache_dir_update_dig_user() is called to replace dig_user, set by digest_cache_get() to the directory digest cache, with the found one. It can also happen that dig_user is updated with a directory digest cache, if the digest is not found and there was a directory modification between get and lookup.

digest_cache_dir_lookup_digest() returns the digest cache reference of the current directory entry as the uintptr_t type, so that callers of digest_cache_lookup() don't mistakenly try to call digest_cache_put() with that reference.

The returned digest cache reference can be converted back to (struct digest_cache *) and used to retrieve information about the digest cache containing the digest, which is not known in advance in the case of directories until the digest search is performed.

Finally, digest_cache_dir_free() releases the digest cache references stored in the list of directory entries, and frees the list itself.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- security/integrity/digest_cache/Makefile | 2 +- security/integrity/digest_cache/dir.c | 273 +++++++++++++++++++++ security/integrity/digest_cache/htable.c | 4 + security/integrity/digest_cache/internal.h | 43 ++++ security/integrity/digest_cache/main.c | 13 + 5 files changed, 334 insertions(+), 1 deletion(-) create mode 100644 security/integrity/digest_cache/dir.c

diff --git a/security/integrity/digest_cache/Makefile b/security/integrity/digest_cache/Makefile index 77dd98a1a07d..aef7f97d1407 100644 --- a/security/integrity/digest_cache/Makefile +++ b/security/integrity/digest_cache/Makefile @@ -4,7 +4,7 @@

obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache.o

-digest_cache-y := main.o secfs.o htable.o populate.o modsig.o verif.o +digest_cache-y := main.o secfs.o htable.o populate.o modsig.o verif.o dir.o

digest_cache-y += parsers/tlv.o digest_cache-y += parsers/rpm.o diff --git a/security/integrity/digest_cache/dir.c b/security/integrity/digest_cache/dir.c new file mode 100644 index 000000000000..f0a2cb9618ba --- /dev/null +++ b/security/integrity/digest_cache/dir.c @@ -0,0 +1,273 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Manage digest caches from directories. + */ + +#define pr_fmt(fmt) "digest_cache: "fmt +#include <linux/init_task.h> +#include <linux/namei.h> + +#include "internal.h" + +/** + * digest_cache_dir_iter - Digest cache directory iterator + * @__ctx: iterate_dir() context + * @name: Name of file in the accessed directory + * @namelen: String length of @name + * @offset: Current position in the directory stream (see man readdir) + * @ino: Inode number + * @d_type: File type + * + * This function stores the names of the files in the containing directory in + * a linked list. If they are in the format <seq num>-<format>-<name>, this + * function orders them by seq num, so that digest lists are processed in the + * desired order. Otherwise, if <seq num>- is not included, it adds the name at + * the end of the list. + * + * Return: True to continue processing, false to stop. + */ +static bool digest_cache_dir_iter(struct dir_context *__ctx, const char *name, + int namelen, loff_t offset, u64 ino, + unsigned int d_type) +{ + struct readdir_callback *ctx = container_of(__ctx, typeof(*ctx), ctx); + struct dir_entry *new_entry, *p; + unsigned int seq_num; + char *separator; + int ret; + + if (!strcmp(name, ".") || !strcmp(name, "..")) + return true; + + if (d_type != DT_REG) + return true; + + new_entry = kmalloc(sizeof(*new_entry) + namelen + 1, GFP_KERNEL); + if (!new_entry) + return false; + + memcpy(new_entry->name, name, namelen); + new_entry->name[namelen] = '\0'; + new_entry->seq_num = UINT_MAX; + new_entry->digest_cache = NULL; + mutex_init(&new_entry->digest_cache_mutex); + + if (new_entry->name[0] < '0' || new_entry->name[0] > '9') + goto out; + + separator = strchr(new_entry->name, '-'); + if (!separator) + goto out; + + *separator = '\0'; + ret = kstrtouint(new_entry->name, 10, &seq_num); + *separator = '-'; + if (ret < 0) + goto out; + + new_entry->seq_num = seq_num; + + list_for_each_entry(p, ctx->head, list) { + if (seq_num <= p->seq_num) { + list_add(&new_entry->list, p->list.prev); + pr_debug("Added %s before %s in dir list\n", + new_entry->name, p->name); + return true; + } + } +out: + list_add_tail(&new_entry->list, ctx->head); + pr_debug("Added %s to tail of dir list\n", new_entry->name); + return true; +} + +/** + * digest_cache_dir_add_entries - Add dir entries to a dir digest cache + * @digest_cache: Dir digest cache + * @digest_list_path: Path structure of the digest list directory + * + * This function iterates over the entries of a directory, and creates a linked + * list of file names from that directory. + * + * Return: Zero on success, a POSIX error code otherwise. + */ +int digest_cache_dir_add_entries(struct digest_cache *digest_cache, + struct path *digest_list_path) +{ + struct file *dir_file; + struct readdir_callback buf = { + .ctx.actor = digest_cache_dir_iter, + .ctx.pos = 0, + .head = &digest_cache->dir_entries, + }; + int ret; + + dir_file = dentry_open(digest_list_path, O_RDONLY, &init_cred); + if (IS_ERR(dir_file)) { + pr_debug("Cannot access %s, ret: %ld\n", digest_cache->path_str, + PTR_ERR(dir_file)); + return PTR_ERR(dir_file); + } + + ret = iterate_dir(dir_file, &buf.ctx); + if (ret < 0) + pr_debug("Failed to iterate directory %s\n", + digest_cache->path_str); + + fput(dir_file); + return ret; +} + +/** + * digest_cache_dir_create - Create and initialize a directory digest cache + * @dentry: Dentry of the file whose digest is looked up + * @digest_list_path: Path structure of the digest list directory (updated) + * @path_str: Path string of the digest list directory + * + * This function creates and initializes (or obtains if it already exists) a + * directory digest cache. It updates the path that digest cache was + * created/obtained from, so that the caller can use it to perform lookup + * operations. + * + * Return: A directory digest cache on success, NULL otherwise. + */ +static struct digest_cache * +digest_cache_dir_create(struct dentry *dentry, struct path *digest_list_path, + char *path_str) +{ + struct digest_cache *digest_cache; + int ret; + + ret = kern_path(path_str, 0, digest_list_path); + if (ret < 0) { + pr_debug("Cannot find path %s\n", path_str); + return NULL; + } + + digest_cache = digest_cache_create(dentry, digest_list_path, path_str, + ""); + if (digest_cache) + digest_cache = digest_cache_init(dentry, digest_cache); + + return digest_cache; +} + +/** + * digest_cache_dir_update_dig_user - Update dig_user with passed digest cache + * @dentry: Dentry of the file whose digest is looked up + * @digest_cache: Dir digest cache + * + * This function updates dig_user of the inode being verified, with the passed + * digest cache. The digest cache can differ if the directory inode was evicted + * or modified, or if the digest searched was found in a directory entry. In the + * latter case, dig_user is replaced with the digest cache of that directory + * entry. + */ +static void digest_cache_dir_update_dig_user(struct dentry *dentry, + struct digest_cache *digest_cache) +{ + struct inode *inode = d_backing_inode(dentry); + struct digest_cache_security *dig_sec; + + dig_sec = digest_cache_get_security(inode); + if (unlikely(!dig_sec)) + return; + + /* Serialize accesses to inode for which the digest cache is used. */ + mutex_lock(&dig_sec->dig_user_mutex); + if (dig_sec->dig_user != digest_cache) { + digest_cache_put(dig_sec->dig_user); + dig_sec->dig_user = digest_cache_ref(digest_cache); + } + mutex_unlock(&dig_sec->dig_user_mutex); +} + +/** + * digest_cache_dir_lookup_digest - Lookup a digest + * @dentry: Dentry of the file whose digest is looked up + * @digest_cache: Dir digest cache + * @digest: Digest to search + * @algo: Algorithm of the digest to search + * + * This function iterates over the linked list created by + * digest_cache_dir_add_entries() and looks up the digest in the digest cache + * of each entry. + * + * Return: A positive uintptr_t value if the digest if found, zero otherwise. + */ +uintptr_t digest_cache_dir_lookup_digest(struct dentry *dentry, + struct digest_cache *digest_cache, + u8 *digest, enum hash_algo algo) +{ + struct dir_entry *dir_entry; + struct digest_cache *dir_cache, *cache, *found = NULL; + struct path digest_list_path; + int ret; + + /* Try to reacquire the dir digest cache, and use the new if changed. */ + dir_cache = digest_cache_dir_create(dentry, &digest_list_path, + digest_cache->path_str); + if (!dir_cache) + return 0UL; + + /* Continue to use the new one. */ + list_for_each_entry(dir_entry, &dir_cache->dir_entries, list) { + mutex_lock(&dir_entry->digest_cache_mutex); + if (!dir_entry->digest_cache) { + cache = digest_cache_create(dentry, &digest_list_path, + dir_cache->path_str, + dir_entry->name); + if (cache) + cache = digest_cache_init(dentry, cache); + + /* Ignore digest caches that cannot be instantiated. */ + if (!cache) { + mutex_unlock(&dir_entry->digest_cache_mutex); + continue; + } + + /* Consume extra ref. from digest_cache_create(). */ + dir_entry->digest_cache = cache; + } + mutex_unlock(&dir_entry->digest_cache_mutex); + + ret = digest_cache_htable_lookup(dentry, + dir_entry->digest_cache, + digest, algo); + if (!ret) { + found = dir_entry->digest_cache; + break; + } + } + + digest_cache_dir_update_dig_user(dentry, found ?: dir_cache); + + digest_cache_put(dir_cache); + path_put(&digest_list_path); + return (uintptr_t)found; +} + +/** + * digest_cache_dir_free - Free the stored file list and put digest caches + * @digest_cache: Dir digest cache + * + * This function frees the file list created by digest_cache_dir_add_entries(), + * and puts the digest cache of each directory entry, if a reference exists. + */ +void digest_cache_dir_free(struct digest_cache *digest_cache) +{ + struct dir_entry *p, *q; + + list_for_each_entry_safe(p, q, &digest_cache->dir_entries, list) { + if (p->digest_cache) + digest_cache_put(p->digest_cache); + + list_del(&p->list); + mutex_destroy(&p->digest_cache_mutex); + kfree(p); + } +} diff --git a/security/integrity/digest_cache/htable.c b/security/integrity/digest_cache/htable.c index 385f81047b0c..1aa884ef18f0 100644 --- a/security/integrity/digest_cache/htable.c +++ b/security/integrity/digest_cache/htable.c @@ -209,6 +209,10 @@ uintptr_t digest_cache_lookup(struct dentry *dentry, { int ret;

+ if (test_bit(IS_DIR, &digest_cache->flags)) + return digest_cache_dir_lookup_digest(dentry, digest_cache, + digest, algo); + ret = digest_cache_htable_lookup(dentry, digest_cache, digest, algo); if (ret < 0) return 0UL; diff --git a/security/integrity/digest_cache/internal.h b/security/integrity/digest_cache/internal.h index 9083a87374a5..34a26576a5aa 100644 --- a/security/integrity/digest_cache/internal.h +++ b/security/integrity/digest_cache/internal.h @@ -17,6 +17,39 @@ #define INIT_IN_PROGRESS 0 /* Digest cache being initialized. */ #define INIT_STARTED 1 /* Digest cache init started. */ #define INVALID 2 /* Digest cache marked as invalid. */ +#define IS_DIR 3 /* Digest cache created from dir. */ + +/** + * struct readdir_callback - Structure to store information for dir iteration + * @ctx: Context structure + * @head: Head of linked list of directory entries + * + * This structure stores information to be passed from the iterate_dir() caller + * to the directory iterator. + */ +struct readdir_callback { + struct dir_context ctx; + struct list_head *head; +}; + +/** + * struct dir_entry - Directory entry + * @list: Linked list of directory entries + * @digest_cache: Digest cache associated to the directory entry + * @digest_cache_mutex: Protects @digest_cache + * @seq_num: Sequence number of the directory entry from file name + * @name: File name of the directory entry + * + * This structure represents a directory entry with a digest cache created + * from that entry. + */ +struct dir_entry { + struct list_head list; + struct digest_cache *digest_cache; + struct mutex digest_cache_mutex; + unsigned int seq_num; + char name[]; +};

/** * struct digest_cache_verif @@ -84,6 +117,7 @@ struct htable { /** * struct digest_cache - Digest cache * @htables: Hash tables (one per algorithm) + * @dir_entries: List of files in a directory and the digest cache * @ref_count: Number of references to the digest cache * @path_str: Path of the digest list the digest cache was created from * @flags: Control flags @@ -95,6 +129,7 @@ struct htable { */ struct digest_cache { struct list_head htables; + struct list_head dir_entries; atomic_t ref_count; char *path_str; unsigned long flags; @@ -208,4 +243,12 @@ size_t digest_cache_strip_modsig(__u8 *data, size_t data_len); /* verif.c */ void digest_cache_verif_free(struct digest_cache *digest_cache);

+/* dir.c */ +int digest_cache_dir_add_entries(struct digest_cache *digest_cache, + struct path *digest_cache_path); +uintptr_t digest_cache_dir_lookup_digest(struct dentry *dentry, + struct digest_cache *digest_cache, + u8 *digest, enum hash_algo algo); +void digest_cache_dir_free(struct digest_cache *digest_cache); + #endif /* _DIGEST_CACHE_INTERNAL_H */ diff --git a/security/integrity/digest_cache/main.c b/security/integrity/digest_cache/main.c index fda6ac599a2d..d050ebad3cbb 100644 --- a/security/integrity/digest_cache/main.c +++ b/security/integrity/digest_cache/main.c @@ -54,6 +54,7 @@ static struct digest_cache *digest_cache_alloc_init(char *path_str, INIT_LIST_HEAD(&digest_cache->htables); INIT_LIST_HEAD(&digest_cache->verif_data); spin_lock_init(&digest_cache->verif_data_lock); + INIT_LIST_HEAD(&digest_cache->dir_entries);

pr_debug("New digest cache %s (ref count: %d)\n", digest_cache->path_str, atomic_read(&digest_cache->ref_count)); @@ -71,6 +72,7 @@ static void digest_cache_free(struct digest_cache *digest_cache) { digest_cache_htable_free(digest_cache); digest_cache_verif_free(digest_cache); + digest_cache_dir_free(digest_cache);

pr_debug("Freed digest cache %s\n", digest_cache->path_str); kfree(digest_cache->path_str); @@ -283,6 +285,17 @@ struct digest_cache *digest_cache_init(struct dentry *dentry, /* Prevent usage of partially-populated digest cache. */ set_bit(INVALID, &digest_cache->flags); } + } else if (S_ISDIR(inode->i_mode)) { + set_bit(IS_DIR, &digest_cache->flags); + + ret = digest_cache_dir_add_entries(digest_cache, + &digest_cache->digest_list_path); + if (ret < 0) { + pr_debug("Failed to add dir entries to dir digest cache, ret: %d (keep digest cache)\n", + ret); + /* Prevent usage of partially-populated digest cache. */ + set_bit(INVALID, &digest_cache->flags); + } }

path_put(&digest_cache->digest_list_path);

From: Roberto Sassu roberto.sassu@huawei.com

Register six new LSM hooks on behalf of the IMA LSM, path_truncate, file_release, inode_unlink, inode_rename, inode_post_setxattr and inode_post_removexattr, to monitor digest lists/parent directory modifications.

If an action affects a digest list or the parent directory, the new LSM hook implementations call digest_cache_reset_clear_owner() to set the RESET bit on the digest cache referenced by dig_owner in the inode security blob, and to put and clear dig_owner itself. This will also cause next calls to digest_cache_get() and digest_cache_dir_lookup_digest() to replace respectively dig_user and the directory entry digest cache.

If an action affects a file using a digest cache, the new LSM hook implementations call digest_cache_clear_user() to clear dig_user in the inode security blob. This will also cause next calls to digest_cache_get() to obtain a new digest cache, based on the updated location.

Callers of digest_cache_get() that previously obtained a reset digest cache are not affected, since that one remains valid as long as the reference count is greater than zero. If they want to know if a reset happened, they can record which digest cache they obtained with digest_cache_get() and compare with the new one from a subsequent digest_cache_get() call.

Recreating a file digest cache means reading the digest list again and extracting the digests. Recreating a directory digest cache, instead, does not mean recreating the digest cache for existing directory entries, since those digest caches are likely already stored in the inode security blob. It would happen however for new directory entries.

Dig_owner reset for file/directory digest caches is done on path_truncate, when a digest list is truncated (there is no inode_truncate, file_truncate does not catch operations through the truncate() system call), file_release, when a digest list opened for write or created is being closed, inode_unlink, when a digest list is removed, and inode_rename when a digest list or the directory itself are renamed.

Directory digest caches are reset even if the current operation involves a file, since that operation might affect the result of the lookup done through them. For example, if one is interested that a digest is not found in a directory, adding a new digest list to that directory could change the result.

Dig_user clear is always done on inode_post_setxattr and inode_post_removexattr, when the security.digest_list xattr is respectively set or removed from a file using a digest cache.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- security/integrity/digest_cache/Makefile | 3 +- security/integrity/digest_cache/dir.c | 6 + security/integrity/digest_cache/internal.h | 13 ++ security/integrity/digest_cache/main.c | 12 ++ security/integrity/digest_cache/reset.c | 227 +++++++++++++++++++++ 5 files changed, 260 insertions(+), 1 deletion(-) create mode 100644 security/integrity/digest_cache/reset.c

diff --git a/security/integrity/digest_cache/Makefile b/security/integrity/digest_cache/Makefile index aef7f97d1407..8847c1ba7d5f 100644 --- a/security/integrity/digest_cache/Makefile +++ b/security/integrity/digest_cache/Makefile @@ -4,7 +4,8 @@

obj-$(CONFIG_INTEGRITY_DIGEST_CACHE) += digest_cache.o

-digest_cache-y := main.o secfs.o htable.o populate.o modsig.o verif.o dir.o +digest_cache-y := main.o secfs.o htable.o populate.o modsig.o verif.o dir.o \ + reset.o

digest_cache-y += parsers/tlv.o digest_cache-y += parsers/rpm.o diff --git a/security/integrity/digest_cache/dir.c b/security/integrity/digest_cache/dir.c index 12d6af13d49e..6b64b7fdc426 100644 --- a/security/integrity/digest_cache/dir.c +++ b/security/integrity/digest_cache/dir.c @@ -227,6 +227,12 @@ uintptr_t digest_cache_dir_lookup_digest(struct dentry *dentry, /* Continue to use the new one. */ list_for_each_entry(dir_entry, &dir_cache->dir_entries, list) { mutex_lock(&dir_entry->digest_cache_mutex); + if (dir_entry->digest_cache && + test_bit(RESET, &dir_entry->digest_cache->flags)) { + digest_cache_put(dir_entry->digest_cache); + dir_entry->digest_cache = NULL; + } + if (!dir_entry->digest_cache) { cache = digest_cache_create(dentry, &digest_list_path, dir_cache->path_str, diff --git a/security/integrity/digest_cache/internal.h b/security/integrity/digest_cache/internal.h index c90efdbf51ed..023e11640af1 100644 --- a/security/integrity/digest_cache/internal.h +++ b/security/integrity/digest_cache/internal.h @@ -21,6 +21,7 @@ #define DIR_PREFETCH 4 /* Prefetch enabled for dir entries. */ #define FILE_PREFETCH 5 /* Prefetch enabled for dir entry. */ #define FILE_READ 6 /* Digest cache for reading file. */ +#define RESET 7 /* Digest cache to be recreated. */

/** * struct readdir_callback - Structure to store information for dir iteration @@ -261,4 +262,16 @@ int digest_cache_dir_prefetch(struct dentry *dentry, struct digest_cache *digest_cache); void digest_cache_dir_free(struct digest_cache *digest_cache);

+/* reset.c */ +int digest_cache_path_truncate(const struct path *path); +void digest_cache_file_release(struct file *file); +int digest_cache_inode_unlink(struct inode *dir, struct dentry *dentry); +int digest_cache_inode_rename(struct inode *old_dir, struct dentry *old_dentry, + struct inode *new_dir, struct dentry *new_dentry); +void digest_cache_inode_post_setxattr(struct dentry *dentry, const char *name, + const void *value, size_t size, + int flags); +void digest_cache_inode_post_removexattr(struct dentry *dentry, + const char *name); + #endif /* _DIGEST_CACHE_INTERNAL_H */ diff --git a/security/integrity/digest_cache/main.c b/security/integrity/digest_cache/main.c index e9c3d120b8d4..99c2f1f85573 100644 --- a/security/integrity/digest_cache/main.c +++ b/security/integrity/digest_cache/main.c @@ -422,6 +422,11 @@ struct digest_cache *digest_cache_get(struct dentry *dentry)

/* Serialize accesses to inode for which the digest cache is used. */ mutex_lock(&dig_sec->dig_user_mutex); + if (dig_sec->dig_user && test_bit(RESET, &dig_sec->dig_user->flags)) { + digest_cache_put(dig_sec->dig_user); + dig_sec->dig_user = NULL; + } + if (!dig_sec->dig_user) { down_read(&default_path_sem); /* Consume extra reference from digest_cache_create(). */ @@ -515,6 +520,13 @@ static void digest_cache_inode_free_security(struct inode *inode) static struct security_hook_list digest_cache_hooks[] __ro_after_init = { LSM_HOOK_INIT(inode_alloc_security, digest_cache_inode_alloc_security), LSM_HOOK_INIT(inode_free_security, digest_cache_inode_free_security), + LSM_HOOK_INIT(path_truncate, digest_cache_path_truncate), + LSM_HOOK_INIT(file_release, digest_cache_file_release), + LSM_HOOK_INIT(inode_unlink, digest_cache_inode_unlink), + LSM_HOOK_INIT(inode_rename, digest_cache_inode_rename), + LSM_HOOK_INIT(inode_post_setxattr, digest_cache_inode_post_setxattr), + LSM_HOOK_INIT(inode_post_removexattr, + digest_cache_inode_post_removexattr), };

/** diff --git a/security/integrity/digest_cache/reset.c b/security/integrity/digest_cache/reset.c new file mode 100644 index 000000000000..003c8ee96d72 --- /dev/null +++ b/security/integrity/digest_cache/reset.c @@ -0,0 +1,227 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2023-2024 Huawei Technologies Duesseldorf GmbH + * + * Author: Roberto Sassu roberto.sassu@huawei.com + * + * Reset digest cache on digest lists/directory modifications. + */ + +#define pr_fmt(fmt) "digest_cache: "fmt +#include "internal.h" + +/** + * digest_cache_reset_clear_owner - Reset and clear dig_owner + * @inode: Inode of the digest list/directory containing the digest list + * @reason: Reason for reset and clear + * + * This function sets the RESET bit of the digest cache referenced by dig_owner + * of the passed inode, and puts and clears dig_owner. + * + * The next time they are called, digest_cache_get() and + * digest_cache_dir_lookup_digest() replace respectively dig_user and the digest + * cache of the directory entry. + */ +static void digest_cache_reset_clear_owner(struct inode *inode, + const char *reason) +{ + struct digest_cache_security *dig_sec; + + dig_sec = digest_cache_get_security(inode); + if (unlikely(!dig_sec)) + return; + + mutex_lock(&dig_sec->dig_owner_mutex); + if (dig_sec->dig_owner) { + pr_debug("Resetting and clearing %s (dig_owner), reason: %s\n", + dig_sec->dig_owner->path_str, reason); + set_bit(RESET, &dig_sec->dig_owner->flags); + digest_cache_put(dig_sec->dig_owner); + dig_sec->dig_owner = NULL; + } + mutex_unlock(&dig_sec->dig_owner_mutex); +} + +/** + * digest_cache_clear_user - Clear dig_user + * @inode: Inode of the file using the digest cache + * @filename: File name of the affected inode + * @reason: Reason for clear + * + * This function clears dig_user in the inode security blob, so that + * digest_cache_get() requests a new digest cache based on the updated digest + * list location. + */ +static void digest_cache_clear_user(struct inode *inode, const char *filename, + const char *reason) +{ + struct digest_cache_security *dig_sec; + + dig_sec = digest_cache_get_security(inode); + if (unlikely(!dig_sec)) + return; + + mutex_lock(&dig_sec->dig_user_mutex); + if (dig_sec->dig_user && !test_bit(RESET, &dig_sec->dig_user->flags)) { + pr_debug("Clearing %s (dig_user of %s), reason: %s\n", + dig_sec->dig_user->path_str, filename, reason); + digest_cache_put(dig_sec->dig_user); + dig_sec->dig_user = NULL; + } + mutex_unlock(&dig_sec->dig_user_mutex); +} + +/** + * digest_cache_path_truncate - A file is being truncated + * @path: File path + * + * This function is called when a file is being truncated. If the inode is a + * digest list and/or the parent is a directory containing digest lists, it + * resets the inode and/or directory dig_owner, to force rebuilding the digest + * cache. + * + * Return: Zero. + */ +int digest_cache_path_truncate(const struct path *path) +{ + struct inode *inode = d_backing_inode(path->dentry); + struct inode *dir = d_backing_inode(path->dentry->d_parent); + + if (!S_ISREG(inode->i_mode)) + return 0; + + digest_cache_reset_clear_owner(inode, "path_truncate(file)"); + digest_cache_reset_clear_owner(dir, "path_truncate(dir)"); + return 0; +} + +/** + * digest_cache_file_release - Last reference of a file desc is being released + * @file: File descriptor + * + * This function is called when the last reference of a file descriptor is + * being released. If the inode is a regular file and was opened for write or + * was created, it resets the inode and the parent directory dig_owner, to + * force rebuilding the digest caches. + */ +void digest_cache_file_release(struct file *file) +{ + struct inode *dir = d_backing_inode(file_dentry(file)->d_parent); + + if (!S_ISREG(file_inode(file)->i_mode) || + ((!(file->f_mode & FMODE_WRITE)) && + !(file->f_mode & FMODE_CREATED))) + return; + + digest_cache_reset_clear_owner(file_inode(file), "file_release(file)"); + digest_cache_reset_clear_owner(dir, "file_release(dir)"); +} + +/** + * digest_cache_inode_unlink - An inode is being removed + * @dir: Inode of the affected directory + * @dentry: Dentry of the inode being removed + * + * This function is called when an existing inode is being removed. If the + * inode is a digest list/digest list directory, or the parent inode is the + * digest list directory and the inode is a regular file, it resets the + * affected inode dig_owner, to force rebuilding the digest cache. + * + * Return: Zero. + */ +int digest_cache_inode_unlink(struct inode *dir, struct dentry *dentry) +{ + struct inode *inode = d_backing_inode(dentry); + + if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode)) + return 0; + + digest_cache_reset_clear_owner(inode, S_ISREG(inode->i_mode) ? + "inode_unlink(file)" : + "inode_unlink(dir)"); + + if (S_ISREG(inode->i_mode)) + digest_cache_reset_clear_owner(dir, "inode_unlink(dir)"); + + return 0; +} + +/** + * digest_cache_inode_rename - An inode is being renamed + * @old_dir: Inode of the directory containing the inode being renamed + * @old_dentry: Dentry of the inode being renamed + * @new_dir: Directory where the inode will be placed into + * @new_dentry: Dentry of the inode after being renamed + * + * This function is called when an existing inode is being moved from a + * directory to another (rename). If the inode is a digest list or the digest + * list directory, or that inode is a digest list moved from/to the digest list + * directory, it resets the affected inode dig_owner, to force rebuilding the + * digest cache. + * + * Return: Zero. + */ +int digest_cache_inode_rename(struct inode *old_dir, struct dentry *old_dentry, + struct inode *new_dir, struct dentry *new_dentry) +{ + struct inode *old_inode = d_backing_inode(old_dentry); + + if (!S_ISREG(old_inode->i_mode) && !S_ISDIR(old_inode->i_mode)) + return 0; + + digest_cache_reset_clear_owner(old_inode, S_ISREG(old_inode->i_mode) ? + "inode_rename(file)" : + "inode_rename(dir)"); + + if (S_ISREG(old_inode->i_mode)) { + digest_cache_reset_clear_owner(old_dir, + "inode_rename(from_dir)"); + digest_cache_reset_clear_owner(new_dir, + "inode_rename(to_dir)"); + } + + return 0; +} + +/** + * digest_cache_inode_post_setxattr - An xattr was set + * @dentry: File + * @name: Xattr name + * @value: Xattr value + * @size: Size of xattr value + * @flags: Flags + * + * This function is called after an xattr was set on an existing inode. If the + * inode points to a digest cache and the xattr set is security.digest_list, it + * puts and clears dig_user in the inode security blob, to force retrieving a + * fresh digest cache. + */ +void digest_cache_inode_post_setxattr(struct dentry *dentry, const char *name, + const void *value, size_t size, int flags) +{ + if (strcmp(name, XATTR_NAME_DIGEST_LIST)) + return; + + digest_cache_clear_user(d_backing_inode(dentry), dentry->d_name.name, + "inode_post_setxattr"); +} + +/** + * digest_cache_inode_post_removexattr - An xattr was removed + * @dentry: File + * @name: Xattr name + * + * This function is called after an xattr was removed from an existing inode. + * If the inode points to a digest cache and the xattr removed is + * security.digest_list, it puts and clears dig_user in the inode security + * blob, to force retrieving a fresh digest cache. + */ +void digest_cache_inode_post_removexattr(struct dentry *dentry, + const char *name) +{ + if (strcmp(name, XATTR_NAME_DIGEST_LIST)) + return; + + digest_cache_clear_user(d_backing_inode(dentry), dentry->d_name.name, + "inode_post_removexattr"); +}

From: Roberto Sassu roberto.sassu@huawei.com

Add the documentation of the Integrity Digest Cache in Documentation/security.

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- Documentation/security/digest_cache.rst | 814 ++++++++++++++++++++++++ Documentation/security/index.rst | 1 + MAINTAINERS | 2 + 3 files changed, 817 insertions(+) create mode 100644 Documentation/security/digest_cache.rst

diff --git a/Documentation/security/digest_cache.rst b/Documentation/security/digest_cache.rst new file mode 100644 index 000000000000..ddc33e672090 --- /dev/null +++ b/Documentation/security/digest_cache.rst @@ -0,0 +1,814 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================== +Integrity Digest Cache +====================== + +Introduction +============ + +Integrity detection and protection has long been a desirable feature, to +reach a large user base and mitigate the risk of flaws in the software +and attacks. + +However, while solutions exist, they struggle to reach a large user base, +due to requiring higher than desired constraints on performance, +flexibility and configurability, that only security conscious people are +willing to accept. + +For example, IMA measurement requires the target platform to collect +integrity measurements, and to protect them with the TPM, which introduces +a noticeable overhead (up to 10x slower in a microbenchmark) on frequently +used system calls, like the open(). + +IMA Appraisal currently requires individual files to be signed and +verified, and Linux distributions to rebuild all packages to include file +signatures (this approach has been adopted from Fedora 39+). Like a TPM, +also signature verification introduces a significant overhead, especially +if it is used to check the integrity of many files. + +This is where the new Integrity Digest Cache comes into play, it offers +additional support for new and existing integrity solutions, to make +them faster and easier to deploy. + +The Integrity Digest Cache can help IMA to reduce the number of TPM +operations and to make them happen in a deterministic way. If IMA knows +that a file comes from a Linux distribution, it can measure files in a +different way: measure the list of digests coming from the distribution +(e.g. RPM package headers), and subsequently measure a file if it is not +found in that list. + +The performance improvement comes at the cost of IMA not reporting which +files from installed packages were accessed, and in which temporal +sequence. This approach might not be suitable for all use cases. + +The Integrity Digest Cache can also help IMA for appraisal. IMA can simply +lookup the calculated digest of an accessed file in the list of digests +extracted from package headers, after verifying the header signature. It is +sufficient to verify only one signature for all files in the package, as +opposed to verifying a signature for each file. + +The same approach can be followed by other LSMs, such as Integrity Policy +Enforcement (IPE), and BPF LSM. + +The Integrity Digest Cache is not tied to a specific package format. While +it currently supports a TLV-based and the RPM formats, it can be easily +extended to support more formats, such as DEBs. Focusing on just extracting +digests keeps these parsers minimal and reasonably simple (e.g. the RPM +parser has ~220 LOC). Included parsers have been verified for memory safety +with the Frama-C static analyzer. The parsers with the Frama-C assertions +are available here: + +https://github.com/robertosassu/rpm-formal/ + +Integrating the Integrity Digest Cache in IMA brings significant +performance improvements: up to 67% and 79% for measurement respectively in +sequential and parallel file reads; up to 65% and 43% for appraisal +respectively in sequential and parallel file reads. + +The performance can be further enhanced by using fsverity digests instead +of conventional file digests, which would make IMA verify only the portion +of the file to be read. However, at the moment, fsverity digests are not +included in RPM packages. In this case, once rpm is extended to include +them, Linux distributions still have to rebuild their packages. + +The Integrity Digest Cache can support both digest types, so that the +functionality is immediately available without waiting for Linux +distributions to do the transition. + + +Design +====== + +Main idea +--------- + +The Integrity Digest Cache extracts digests from a file, referred to as a +digest list, and stores them in kernel memory in a structure named +digest_cache. + +The digest_cache structure contains a set of per algorithm hash tables, +where digests are stored, the digest list pathname, a reference counter, +and the integrity state of the digest list. + +If a digest cache is created from a directory, its hash tables are empty +and instead it contains a snapshot of the directory entries discovered with +iterate_dir(). + +The integrity state of digest caches created from regular files, also +called verification data, is evaluated independently by LSMs, for example +by verifying the signature of the digest list, and is provided to the +Integrity Digest Cache through a dedicated API. + +The extracted digests can be used as reference values initially for +integrity verification of file data and at a later stage for integrity +verification of file metadata. + +The Integrity Digest Cache can extract digests from a digest list, provided +that it has a parser for its format. + + +Caching and reference counting +------------------------------ + +Creating a digest cache every time it is requested would introduce an +unnecessary overhead, due to repeating the same operation. For this reason, +the Integrity Digest Cache reserves space in the inode security blob +(through IMA) and stores two types of digest cache reference. + +If the digest cache was created from the same inode, the Integrity Digest +Cache stores in the inode security blob a reference called dig_owner, +because the inode owns the content. + +If the digest cache was requested for verifying an inode, the Integrity +Digest Cache stores a reference called dig_user, because the inode is a +user of the digest cache. + +An inode can have both types of reference set, if it is a digest list +to be verified with another digest list. + +Check and assignemt of dig_owner and dig_user is protected respectively +with the dig_owner_mutex and dig_user_mutex mutexes. + +The digest cache reference count tracks how many references have been made +to that digest cache (whether that reference is stored in the inode +security blob, or is returned to a user of the Integrity Digest Cache). + +Only when the reference count reaches zero, i.e. all references have been +released, the digest cache can be freed. + + +Digest cache lifecycle +---------------------- + +Digest cache request +~~~~~~~~~~~~~~~~~~~~ + +The first step in order to query a digest from a digest list is to request +a digest cache, by calling digest_cache_get(). The Integrity Digest Cache +takes care of the digest cache creation and initialization processes, +transparently to the caller. + +The caller passes as argument to digest_cache_get() the inode that the +caller intends to verify. The Integrity Digest Cache first sees if there +is a cached digest cache in that inode (dig_user reference). If there is, +it immediately returns the digest cache with the reference count increased, +since the reference is returned to the caller. + +Otherwise, it will perform the necessary steps (below) to obtain one. + + +Digest list lookup +~~~~~~~~~~~~~~~~~~ + +In order to build a digest cache and return it to the caller for performing +a query, the Integrity Digest Cache must know which digest list to use. +There are a few alternatives. + +(1) There is only one digest list and its path is specified as default +location at build-time in the kernel configuration or at run-time through +securityfs. The Integrity Digest Cache builds a single digest cache from +that digest list and returns it to the caller. + +(2) The default location is a directory containing multiple digest lists. +Unlike (1), the Integrity Digest Cache does not know which digest list to +select, and creates a directory digest cache with a snapshot of the +directory entries. During a query, the Integrity Digest Cache iteratively +creates a digest cache for each directory entry and searches for the digest +until there is a match. + +(3) Same as (2), but the digest list file name is stored as value of the +new security.digest_list xattr in the inode for which the digest cache is +requested. The Integrity Digest Cache can directly retrieve the digest list +using the default directory as the base path and the xattr value as last +path component. + +(4) Similar to (3), but the Integrity Digest Cache still creates a +directory digest cache like in (2). Then, it only reads the digest list if +the directory entry file name does not match the security.digest_list +xattr, to trigger a measurement or, otherwise, creates a digest cache from +the matching one. This is also known as the prefetching mechanism, +introduced later. + + +Digest cache creation +~~~~~~~~~~~~~~~~~~~~~ + +Once the Integrity Digest Cache selected the digest list to use, it looks +up the digest list inode through the VFS, verifies whether in the inode +security blob there is already a digest cache reference (dig_owner). + +If there is, it returns that to digest_cache_get() with the reference count +increased, which in turn will store it in dig_user and will increment the +reference count again before returning to the caller. + +If there isn't, it creates a new digest cache and performs the same steps +as if dig_owner exists. + + +Digest cache initialization +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The digest cache creation does not include initialization and adding the +digests. It cannot be done inside the dig_owner_mutex and dig_user_mutex, +to avoid lock inversion with the inode lock done by the VFS. + +Digest cache initialization is done by digest_cache_get() by +calling digest_cache_init(), after releasing the dig_user_mutex. Any +digest_cache_get() caller can potentially initialize a digest cache. + +To avoid multiple initialization attempts, callers atomically test and set +the INIT_STARTED atomic flag. The first seeing the flag cleared is the one +in charge of the initialization. The other callers wait for another atomic +flag, INIT_IN_PROGRESS to be cleared to zero (it is set to one on digest +cache creation). + +Failures during initialization can be detected by checking the INVALID flag +in the digest cache and, in this case, the digest cache is not returned to +the caller of digest_cache_get(). + + +Digest list naming convention +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The digest_cache_get() caller performing the digest cache initialization +reads the digest list and calls the appropriate parser to extract the +digests, based on the file name prefix. + +The expected digest list file name format is:: + + <digest list format>-<file name> + +where format can be for example ``tlv`` or ``rpm``, which make the +Integrity Digest Cache call respectively the TLV or RPM parser. + +Alternatively, also the following format is supported:: + + <seq num>-<digest list format>-<file name> + +``<seq num>-`` defines how directory entries should be ordered in the +directory digest cache. If present, directory entries are ordered in +ascending way by that number. + + +Digest list parsing +^^^^^^^^^^^^^^^^^^^ + +The selected digest list parser first calls digest_cache_htable_init() to +create the hash tables in the digest cache, once for each hash algorithm +of the digests to be added. digest_cache_htable_init() accepts as parameter +the number of digests to add, usually known before adding digests. + +The number of hash table slots is determined by dividing the number of +digests to add by the desired average collision depth. The latter can be +changed in the kernel configuration, to have a different tradeoff between +digest lookup speed and memory occupation. + +The parser then calls digest_cache_htable_add(), to add extracted digests +to the new hash tables. It can also call digest_cache_htable_lookup() to +check for duplicate digests. + +Directory digest cache +^^^^^^^^^^^^^^^^^^^^^^ + +If the digest list location is a directory, digest_cache_init() calls +digest_cache_dir_add_entries(), which in turn calls iterate_dir() to +get the current directory entries and to add them to a linked list. + +When a digest is looked up on a directory digest cache, +digest_cache_dir_lookup_digest() will create a regular digest cache for +each directory entry and will lookup into it until it finds the digest. + +digest_cache_dir_lookup_digest() also gets a digest cache reference for +each directory entry, so that digest lookup is faster at the next call. + + +Digest lookup +~~~~~~~~~~~~~ + +After a caller of digest_cache_get() obtains the desired digest cache, it +can perform operations on it. The most important operation is querying for +a digest, which can be performed by calling digest_cache_lookup(). + +digest_cache_lookup() returns a numeric reference (uintptr_t type), +representing the digest cache containing the queried digest. It is not a +pointer, to avoid it being accidentally passed to digest_cache_put(). + +If digest_cache_get() returned a directory digest cache, +digest_cache_lookup() cannot directly perform the search, since its hash +tables are empty. Instead, it calls digest_cache_dir_lookup_digest(), +which searches the digest in the digest cache of each directory entry. + +digest_cache_dir_lookup_digest(), if it finds a digest in a directory +digest cache, it calls digest_cache_dir_update_dig_user() to update +dig_user of the inode, whose digest is queried, with the digest cache +containing the digest. This ensures that next time digest_cache_get() is +called for the same inode, the digest is searched in the right digest +cache, instead of repeating the search in each directory entry. + + +Verification data +~~~~~~~~~~~~~~~~~ + +Until now, the caller of the Integrity Digest Cache is assumed to always +trust the returned digest cache from being created from authentic data. Or, +there are security measures in place but not able to correlate reading a +digest list with building a digest cache from it. + +The Integrity Digest Cache introduces a new mechanism for integrity +providers to store verification data, i.e. their evaluation result of a +digest list. It also allows callers of digest_cache_get() to later retrieve +that information and decide whether or not they should use that digest +cache. + +It achieves that by reserving space in the file descriptor security blob, +and by setting the digest cache pointer in the digest list file descriptor +before the digest list is read by the kernel. + +Integrity providers should implement the kernel_post_read_file LSM hook and +call digest_cache_verif_set(), passing the same digest list file descriptor +on which the digest cache pointer was set, their unique ID and their +evaluation result of the digest list. + +The Integrity Digest Cache supports multiple integrity providers at the +same time, since multiple LSMs can implement the kernel_post_read_file LSM +hook. Each provider is expected to choose an unique ID, so that the +verification data can be given back through the same ID. + +Callers of digest_cache_get() can call digest_cache_verif_get() to get +the verification data, passing the returned digest cache pointer and the +desired integrity provider ID. However, if the digest cache returned was +created from a directory, that call results in a NULL pointer, since the +directory digest cache is not populated from any digest list. + +In that case, those callers have to call digest_cache_lookup() to get the +numeric reference of the digest cache containing the digest (thus populated +from a digest list), and pass it to digest_cache_verif_get() after casting +the value to a digest cache pointer. + + +Tracking digest cache changes +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +After a digest cache has been built and its pointer has been set in the +inode security blob, it might happen that there are changes in the digest +lists, in the default directory and in the value of the +security.digest_list xattr. + +All these changes may influence which digest cache is returned to callers +of digest_cache_get() and which digests in the digest cache might be +searched. + +The Integrity Digest Cache monitors such changes by registering to multiple +LSM hooks (path_truncate, file_release, inode_unlink, inode_rename, +inode_post_setxattr and inode_post_removexattr). Except for the last two, +it accesses the dig_owner pointer in the affected inode security blob, sets +the RESET bit, puts the digest cache and clears dig_owner itself. + +The next time that digest cache is requested with digest_cache_get(), also +dig_user is put and cleared. The same happens in +digest_cache_dir_lookup_digest(), where the digest cache of a directory +entry is released and cleared as well. After a reset, a new digest cache is +created and returned, as if there wasn't one in the first place. + +For the last two hooks, when the security.digest_list xattr is modified, +dig_user is cleared so that at the next digest_cache_get() call a new +digest cache is retrieved, since the location of the digest list might have +changed. + +Nothing changes for previous callers of digest_cache_get(), since they +still hold the old digest cache pointer, despite that has been replaced in +the inode security blobs. The old digest cache pointer will be still valid +until the callers decide to release that digest cache. + + +Security decision update after digest cache changes +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +While new calls to digest_cache_get() result in a new digest cache to be +returned, resetting the previous digest cache does not reflect in a reset +of possibly cached security decisions by users of the Integrity Digest +Cache. + +One possible way for those users to become aware of a digest cache change +is to store the digest cache pointer they used for a security decision, to +call digest_cache_get() again during a new file access and to compare the +two pointers. The previous pointer remains valid until the digest cache +is released. + +IMA stores the current digest cache pointer in its managed metadata. At +every file access, it calls digest_cache_get() again and compares the +returned pointer with the one previously stored. If the pointers are the +same, IMA continues to use the previous evaluation result. If not, it +performs the evaluation again. + +The cost of this check is very small. In the case where the digest cache +didn't change since the last digest_cache_get(), the cost is to check if +the dig_user pointer is not NULL, and to increment and decrement the digest +cache reference count. + +In terms of memory, this solution requires IMA to store an additional +pointer in its metadata. + + +Prefetching mechanism +~~~~~~~~~~~~~~~~~~~~~ + +One of the objectives of the Integrity Digest Cache is to make a TPM PCR +predictable, by having digest lists measured in a deterministic order. +Without the prefetching mechanism, digest lists are measured in a +non-deterministic order, since the inodes for which a digest cache can be +requested are accessed in a non-deterministic order too. + +The prefetching mechanism, when enabled by setting the new +security.dig_prefetch xattr to 1, forces digest lists to be looked up by +their file name in the digest cache created for the parent directory. + +The predictability of the PCR is ensured by reading both matching and +non-matching digest lists during the search, so that integrity providers +can measure them, and by only creating a digest cache for the matching one. +In this way, it does not matter if a digest list later in the list of +directory entries is requested before a earlier one, since all digest lists +until that point are measured anyway. + +However, while this mechanism ensures predictability of the PCR, it could +also introduce significant latencies, especially if the matching digest +list is very late in the list of directory entries. Before a digest cache +is returned from that digest list, hundreds or thousands of digest lists +could have to be read first. + +Then, the ``[<seq num>-]`` prefix in the digest list file name comes at +hand, since it determines the order of directory entries in the directory +digest cache (entries with lower seq nums are before entries with higher +seq nums). Digest lists without that prefix are added at the end of the +directory entries list, in the same order as iterate_dir() shows them. + +Boot performance can be greatly improved by looking at the IMA measurement +list and by seeing in which order digest lists are requested at boot. Then, +``[<seq num>-]`` can be appended to directory entries depending on their +position in the measurement list. + +While digest lists can be requested in a slightly different order due to +the non-deterministic access to inodes, the differences should be minimal, +causing only fewer extra digest lists to be read before the right one is +found. + +Ordering directory entries can also improve digest queries requiring +iteration on all digest lists in the default directory. If directory +entries are ordered by their appearance in the IMA measurement list, a +digest is found faster because most likely it is searched in the same +order as when the IMA measurement list was recorded, and thus its +digest list comes earlier than the others in the list of the directory +entries of the directory digest cache. + + +Release a digest cache +~~~~~~~~~~~~~~~~~~~~~~ + +The Integrity Digest Cache uses the reference count mechanism to ensure +that a digest cache does not simply disappear when someone is using it. + +Either when an inode is evicted from memory, or a caller of +digest_cache_get() finished to use a digest cache, they should call +digest_cache_put() to signal to the Integrity Digest Cache that they are no +longer interested in that digest cache and that it can be eventually freed. + +A digest cache is freed when all digest cache users called +digest_cache_put(), and the reference count reached the value zero. + + +Formal verification of concurrency +================================== + +The Integrity Digest Cache has been designed to work in a heavily concurrent +environment, where code can be executed as a follow up of a VFS operation, +or upon a direct request by a user of the Integrity Digest Cache. + +For this reason, a sound locking mechanism is necessary to protect data +structures against concurrent accesses. + +The first verification of the locking mechanism was done with the in-kernel +lockdep, which can detect potential deadlocks and unsafe usage of the +locking primitives. + +There is an ongoing verification with a tool named Dartagnan, reachable at +the following URL: + +https://github.com/hernanponcedeleon/Dat3M + +This verification required porting the Integrity Digest Cache to user +space, and to simulate concurrent requests through the pthread library. + +Dartagnan explores all thread interleavings and checks for data races. In +addition to lockdep, it can also spot for example improperly guarded +variables. + + +Data structures and API +======================= + +Data structures +--------------- + +These are the data structures defined and used internally by the +Integrity Digest Cache. + +.. kernel-doc:: security/integrity/digest_cache/internal.h + + +Public API +---------- + +This API is meant to be used by users of the Integrity Digest Cache. + +.. kernel-doc:: security/integrity/digest_cache/main.c + :identifiers: digest_cache_get digest_cache_put + +.. kernel-doc:: security/integrity/digest_cache/htable.c + :identifiers: digest_cache_lookup + +.. kernel-doc:: security/integrity/digest_cache/verif.c + :identifiers: digest_cache_verif_set digest_cache_verif_get + + +Parser API +---------- + +This API is meant to be used by digest list parsers. + +.. kernel-doc:: security/integrity/digest_cache/htable.c + :identifiers: digest_cache_htable_init + digest_cache_htable_add + digest_cache_htable_lookup + + +Digest list formats +=================== + +tlv +--- + +The Type-Length-Value (TLV) format was chosen for its extensibility. +Additional fields can be added without breaking compatibility with old +versions of the parser. + +The layout of a tlv digest list is the following:: + + [header: DIGEST_LIST_FILE, num fields, total len] + [field: DIGEST_LIST_ALGO, length, value] + [field: DIGEST_LIST_ENTRY#1, length, value (below)] + |- [header: DIGEST_LIST_ENTRY_DATA, num fields, total len] + |- [DIGEST_LIST_ENTRY_DIGEST#1, length, file digest] + |- [DIGEST_LIST_ENTRY_PATH#1, length, file path] + [field: DIGEST_LIST_ENTRY#N, length, value (below)] + |- [header: DIGEST_LIST_ENTRY_DATA, num fields, total len] + |- [DIGEST_LIST_ENTRY_DIGEST#N, length, file digest] + |- [DIGEST_LIST_ENTRY_PATH#N, length, file path] + +DIGEST_LIST_ALGO is a field to specify the algorithm of the file digest. +DIGEST_LIST_ENTRY is a nested TLV structure with the following fields: +DIGEST_LIST_ENTRY_DIGEST contains the file digest; DIGEST_LIST_ENTRY_PATH +contains the file path. + + +rpm +--- + +The rpm digest list is basically a subset of the RPM package header. +Its format is:: + + [RPM magic number] + [RPMTAG_IMMUTABLE] + +RPMTAG_IMMUTABLE is a section of the full RPM header containing the part +of the header that was signed, and whose signature is stored in the +RPMTAG_RSAHEADER section. + + +Appended signature +------------------ + +Digest lists can have a module-style appended signature, that can be used +for appraisal with IMA. The signature type can be PKCS#7, as for kernel +modules, or a different type. + + +History +======= + +The original name of this work was IMA Digest Lists, which was somehow +considered too invasive. The code was moved to a separate component named +DIGLIM (DIGest Lists Integrity Module), with the purpose of removing the +complexity away of IMA, and also adding the possibility of using it with +other kernel components (e.g. Integrity Policy Enforcement, or IPE). + +The design changed significantly, so DIGLIM was renamed to Integrity Digest +Cache, as the name better reflects what the new component does. + +Since it was originally proposed, in 2017, this work grew up a lot thanks +to various comments/suggestions. It became integrally part of the openEuler +distribution since end of 2020. + +The most important difference between the old the current version is moving +from a centralized repository of file digests to a per-package repository. +This reduces the digest lookup time, since digests are searched in smaller +hash tables, and significantly reduces the memory pressure, since +digest lists are loaded into kernel memory only when they are actually +needed, and removed during reclamation. + + +Performance +=========== + +System specification +-------------------- + +The tests have been performed on a Fedora 38 virtual machine with 4 cores +(AMD EPYC-Rome, no hyperthreading), 16 GB of RAM, no TPM/TPM passthrough/ +emulated. The QEMU process has been pinned to 4 real CPU cores and its +priority was set to -20. + + +Benchmark tool +-------------- + +The Integrity Digest Cache has been tested with an ad-hoc benchmark tool +that creates 20000 files with a random size up to 100 bytes and randomly +adds their digest to one of 303 digest lists. The number of digest lists +has been derived from the ratio (66) digests/packages (124174/1883) found +in the testing virtual machine (hence, 20000/66 = 303). IMA signatures have +been done with ECDSA NIST P-384. + +The benchmark tool then creates a list of 20000 files to be accessed, +randomly chosen (there can be duplicates). This is necessary to make the +results reproducible across reboots (by always replaying the same +operations). The benchmark reads (sequentially and in parallel) the files +from the list 2 times, flushing the kernel caches before each read. + +Each test has been performed 5 times, and the average value is taken. + + +Purpose of the benchmark +------------------------ + +The purpose of the benchmark is to show the performance difference of IMA +between the current behavior, and by using the Integrity Digest Cache. + + +IMA measurement policy: no cache +-------------------------------- + +.. code-block:: bash + + measure func=FILE_CHECK fowner=2001 pcr=12 + + +IMA measurement policy: cache +----------------------------- + +.. code-block:: bash + + measure func=DIGEST_LIST_CHECK pcr=12 + measure func=FILE_CHECK fowner=2001 digest_cache=data pcr=12 + + +IMA measurement results +----------------------- + +Sequential +~~~~~~~~~~ + +This test was performed reading files sequentially, and waiting for the +current read to terminate before beginning a new one. + +:: + + +-------+------------------------+-----------+ + | meas. | time no/p/vTPM (sec.) | slab (KB) | + +--------------------+-------+------------------------+-----------+ + | no cache | 12313 | 31.71 / 102.80 / 46.29 | 86802 | + +--------------------+-------+------------------------+-----------+ + | cache, no prefetch | 304 | 32.21 / 34.28 / 32.47 | 83709 | + +--------------------+-------+------------------------+-----------+ + | cache, prefetch | 304 | 32.67 / 34.47 / 32.67 | 83720 | + +--------------------+-------+------------------------+-----------+ + +The table shows that 12313 measurements (boot_aggregate + files) have been +made without the digest cache, and 304 with the digest cache +(boot_aggregate + digest lists). Consequently, the memory occupation +without the cache is higher due to the higher number of measurements. + +Not surprisingly, for the same reason, also the test time is significantly +higher without the digest cache when the physical or virtual TPM is used. + +In terms of pure performance, first number in the third column, it can be +seen that there are not significant performance differences between using +or not using the digest cache. + +Prefetching adds little overhead, because digest lists were ordered +according to their appearance in the IMA measurement list (which minimize +the digest lists to prefetch). + + +Parallel +~~~~~~~~ + +This test was performed reading files in parallel, not waiting for the +current read to terminate. + +:: + + +-------+-----------------------+-----------+ + | meas. | time no/p/vTPM (sec.) | slab (KB) | + +--------------------+-------+-----------------------+-----------+ + | no cache | 12313 | 15.84 / 79.26 / 23.43 | 87635 | + +--------------------+-------+-----------------------+-----------+ + | cache, no prefetch | 304 | 15.97 / 16.64 / 16.09 | 89890 | + +--------------------+-------+-----------------------+-----------+ + | cache, prefetch | 304 | 16.18 / 16.84 / 16.24 | 85738 | + +--------------------+-------+-----------------------+-----------+ + +Also in this case, the physical TPM causes the biggest delay especially +without digest cache, where a higher number of measurements need to be +extended in the TPM. + +The Integrity Digest Cache does not introduce a noticeable overhead in all +scenarios. + + +IMA appraisal policy: no cache +------------------------------ + +.. code-block:: bash + + appraise func=FILE_CHECK fowner=2001 + + +IMA appraisal policy: cache +--------------------------- + +.. code-block:: bash + + appraise func=DIGEST_LIST_CHECK + appraise func=FILE_CHECK fowner=2001 digest_cache=data + + +IMA appraisal results +--------------------- + +Sequential +~~~~~~~~~~ + +This test was performed reading files sequentially, and waiting for the +current read to terminate before beginning a new one. + +:: + + +-------------+-------------+-----------+ + | files | time (sec.) | slab (KB) | + +----------------------------+-------------+-------------+-----------+ + | appraise (ECDSA sig) | 12312 | 98.10 | 80842 | + +----------------------------+-------------+-------------+-----------+ + | appraise (cache) | 12312 + 303 | 34.09 | 83138 | + +----------------------------+-------------+-------------+-----------+ + | appraise (cache, prefetch) | 12312 + 303 | 34.08 | 83410 | + +----------------------------+-------------+-------------+-----------+ + +This test shows a huge performance difference from verifying the signature +of 12312 files as opposed to just verifying the signature of 303 digest +lists, and looking up the digest of the files being read. + +There are some differences in terms of memory occupation, which is quite +expected due to the fact that we have to take into account the digest +caches loaded in memory, while with the standard appraisal they don't +exist. + + +Parallel +~~~~~~~~ + +This test was performed reading files in parallel, not waiting for the +current read to terminate. + +:: + + +-------------+-------------+-----------+ + | files | time (sec.) | slab (KB) | + +----------------------------+-------------+-------------+-----------+ + | appraise (ECDSA sig) | 12312 | 29.00 | 82255 | + +----------------------------+-------------+-------------+-----------+ + | appraise (cache) | 12313 + 303 | 16.51 | 88359 | + +----------------------------+-------------+-------------+-----------+ + | appraise (cache, prefetch) | 12313 + 303 | 17.08 | 86266 | + +----------------------------+-------------+-------------+-----------+ + +The difference is less marked when performing the read in parallel. Also, +more memory seems to be occupied in the non-prefetch case. + + +How to test +=========== + +Please follow the instructions here: + +https://github.com/linux-integrity/digest-cache-tools diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst index 59f8fc106cb0..34933e13c509 100644 --- a/Documentation/security/index.rst +++ b/Documentation/security/index.rst @@ -19,3 +19,4 @@ Security Documentation digsig landlock secrets/index + digest_cache diff --git a/MAINTAINERS b/MAINTAINERS index ba8d5c137bef..3b212c747652 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -11115,8 +11115,10 @@ R: Eric Snowberg eric.snowberg@oracle.com L: linux-integrity@vger.kernel.org S: Supported T: git git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git +F: Documentation/security/digest_cache.rst F: security/integrity/ F: security/integrity/ima/ +F: tools/testing/selftests/digest_cache/

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