On Mon Apr 15, 2024 at 5:24 PM EEST, Roberto Sassu wrote:
From: Roberto Sassu roberto.sassu@huawei.com
Add the digest_cache_path file in securityfs, 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/digest_cache/Kconfig | 4 ++ security/digest_cache/Makefile | 2 +- security/digest_cache/internal.h | 1 + security/digest_cache/main.c | 10 +++- security/digest_cache/secfs.c | 87 ++++++++++++++++++++++++++++++++ 5 files changed, 102 insertions(+), 2 deletions(-) create mode 100644 security/digest_cache/secfs.c
diff --git a/security/digest_cache/Kconfig b/security/digest_cache/Kconfig index e53fbf0779d6..dfabe5d6e3ca 100644 --- a/security/digest_cache/Kconfig +++ b/security/digest_cache/Kconfig @@ -14,3 +14,7 @@ config DIGEST_LIST_DEFAULT_PATH default "/etc/digest_lists" help Default directory where digest_cache LSM 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/digest_cache/Makefile b/security/digest_cache/Makefile index 48848c41253e..1330655e33b1 100644 --- a/security/digest_cache/Makefile +++ b/security/digest_cache/Makefile @@ -4,4 +4,4 @@ obj-$(CONFIG_SECURITY_DIGEST_CACHE) += digest_cache.o -digest_cache-y := main.o +digest_cache-y := main.o secfs.o diff --git a/security/digest_cache/internal.h b/security/digest_cache/internal.h index 5f04844af3a5..bbf5eefe5c82 100644 --- a/security/digest_cache/internal.h +++ b/security/digest_cache/internal.h @@ -49,6 +49,7 @@ struct digest_cache_security { extern struct lsm_blob_sizes digest_cache_blob_sizes; 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) diff --git a/security/digest_cache/main.c b/security/digest_cache/main.c index 14dba8915e99..661c8d106791 100644 --- a/security/digest_cache/main.c +++ b/security/digest_cache/main.c @@ -18,6 +18,9 @@ static struct kmem_cache *digest_cache_cache __read_mostly; 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
@@ -274,9 +277,12 @@ 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) {
/* Consume extra reference from digest_cache_create(). */ dig_sec->dig_user = digest_cache_new(dentry);down_read(&default_path_sem);
up_read(&default_path_sem);
- }
if (dig_sec->dig_user) /* Increment ref. count for reference returned to the caller. */ @@ -386,6 +392,8 @@ static const struct lsm_id digest_cache_lsmid = { */ static int __init digest_cache_init(void) {
- init_rwsem(&default_path_sem);
- digest_cache_cache = kmem_cache_create("digest_cache_cache", sizeof(struct digest_cache), 0, SLAB_PANIC,
diff --git a/security/digest_cache/secfs.c b/security/digest_cache/secfs.c new file mode 100644 index 000000000000..d3a37bf3588e --- /dev/null +++ b/security/digest_cache/secfs.c @@ -0,0 +1,87 @@ +// 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 digest_cache LSM.
- */
+#define pr_fmt(fmt) "DIGEST CACHE: "fmt +#include <linux/security.h>
+#include "internal.h"
+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,
+};
+static int __init digest_cache_path_init(void) +{
- default_path_dentry = securityfs_create_file("digest_cache_path", 0660,
NULL, NULL,
&default_path_ops);
- if (IS_ERR(default_path_dentry))
return -EFAULT;
Nit: when overwriting error value with another error value it would be best to document it with an inline comment. Otherwise, it is fine.
- return 0;
+}
+late_initcall(digest_cache_path_init);
BR, Jarkko