From: Mickaël Salaün mic@linux.microsoft.com

Process's credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy.

Cc: James Morris jmorris@namei.org Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Reviewed-by: Jann Horn jannh@google.com Acked-by: Serge Hallyn serge@hallyn.com Reviewed-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20210324191520.125779-4-mic@digikod.net ---

Changes since v30: * Add Reviewed-by Kees Cook.

Changes since v28: * Add Acked-by Serge Hallyn.

Changes since v25: * Rename function to landlock_add_cred_hooks().

Changes since v23: * Add an early check for the current domain in hook_cred_free() to avoid superfluous call. * Cosmetic cleanup to make the code more readable.

Changes since v22: * Add Reviewed-by Jann Horn.

Changes since v21: * Fix copyright dates.

Changes since v17: * Constify returned domain pointers from landlock_get_current_domain() and landlock_get_task_domain() helpers.

Changes since v15: * Optimize landlocked() for current thread. * Display the greeting message when everything is initialized.

Changes since v14: * Uses pr_fmt from common.h . * Constify variables. * Remove useless NULL initialization.

Changes since v13: * totally get ride of the seccomp dependency * only keep credential management and LSM setup.

Previous changes: https://lore.kernel.org/lkml/20191104172146.30797-4-mic@digikod.net/ --- security/Kconfig | 10 +++---- security/landlock/Makefile | 3 +- security/landlock/common.h | 20 +++++++++++++ security/landlock/cred.c | 46 ++++++++++++++++++++++++++++++ security/landlock/cred.h | 58 ++++++++++++++++++++++++++++++++++++++ security/landlock/setup.c | 31 ++++++++++++++++++++ security/landlock/setup.h | 16 +++++++++++ 7 files changed, 178 insertions(+), 6 deletions(-) create mode 100644 security/landlock/common.h create mode 100644 security/landlock/cred.c create mode 100644 security/landlock/cred.h create mode 100644 security/landlock/setup.c create mode 100644 security/landlock/setup.h

diff --git a/security/Kconfig b/security/Kconfig index 15a4342b5d01..0ced7fd33e4d 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -278,11 +278,11 @@ endchoice

config LSM string "Ordered list of enabled LSMs" - default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK - default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR - default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO - default "lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC - default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf" + default "landlock,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK + default "landlock,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR + default "landlock,lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO + default "landlock,lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC + default "landlock,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf" help A comma-separated list of LSMs, in initialization order. Any LSMs left off this list will be ignored. This can be diff --git a/security/landlock/Makefile b/security/landlock/Makefile index d846eba445bb..041ea242e627 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,3 +1,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

-landlock-y := object.o ruleset.o +landlock-y := setup.o object.o ruleset.o \ + cred.o diff --git a/security/landlock/common.h b/security/landlock/common.h new file mode 100644 index 000000000000..5dc0fe15707d --- /dev/null +++ b/security/landlock/common.h @@ -0,0 +1,20 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Common constants and helpers + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_COMMON_H +#define _SECURITY_LANDLOCK_COMMON_H + +#define LANDLOCK_NAME "landlock" + +#ifdef pr_fmt +#undef pr_fmt +#endif + +#define pr_fmt(fmt) LANDLOCK_NAME ": " fmt + +#endif /* _SECURITY_LANDLOCK_COMMON_H */ diff --git a/security/landlock/cred.c b/security/landlock/cred.c new file mode 100644 index 000000000000..6725af24c684 --- /dev/null +++ b/security/landlock/cred.c @@ -0,0 +1,46 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Credential hooks + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/cred.h> +#include <linux/lsm_hooks.h> + +#include "common.h" +#include "cred.h" +#include "ruleset.h" +#include "setup.h" + +static int hook_cred_prepare(struct cred *const new, + const struct cred *const old, const gfp_t gfp) +{ + struct landlock_ruleset *const old_dom = landlock_cred(old)->domain; + + if (old_dom) { + landlock_get_ruleset(old_dom); + landlock_cred(new)->domain = old_dom; + } + return 0; +} + +static void hook_cred_free(struct cred *const cred) +{ + struct landlock_ruleset *const dom = landlock_cred(cred)->domain; + + if (dom) + landlock_put_ruleset_deferred(dom); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(cred_prepare, hook_cred_prepare), + LSM_HOOK_INIT(cred_free, hook_cred_free), +}; + +__init void landlock_add_cred_hooks(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/cred.h b/security/landlock/cred.h new file mode 100644 index 000000000000..5f99d3decade --- /dev/null +++ b/security/landlock/cred.h @@ -0,0 +1,58 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Credential hooks + * + * Copyright © 2019-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2019-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_CRED_H +#define _SECURITY_LANDLOCK_CRED_H + +#include <linux/cred.h> +#include <linux/init.h> +#include <linux/rcupdate.h> + +#include "ruleset.h" +#include "setup.h" + +struct landlock_cred_security { + struct landlock_ruleset *domain; +}; + +static inline struct landlock_cred_security *landlock_cred( + const struct cred *cred) +{ + return cred->security + landlock_blob_sizes.lbs_cred; +} + +static inline const struct landlock_ruleset *landlock_get_current_domain(void) +{ + return landlock_cred(current_cred())->domain; +} + +/* + * The call needs to come from an RCU read-side critical section. + */ +static inline const struct landlock_ruleset *landlock_get_task_domain( + const struct task_struct *const task) +{ + return landlock_cred(__task_cred(task))->domain; +} + +static inline bool landlocked(const struct task_struct *const task) +{ + bool has_dom; + + if (task == current) + return !!landlock_get_current_domain(); + + rcu_read_lock(); + has_dom = !!landlock_get_task_domain(task); + rcu_read_unlock(); + return has_dom; +} + +__init void landlock_add_cred_hooks(void); + +#endif /* _SECURITY_LANDLOCK_CRED_H */ diff --git a/security/landlock/setup.c b/security/landlock/setup.c new file mode 100644 index 000000000000..8661112fb238 --- /dev/null +++ b/security/landlock/setup.c @@ -0,0 +1,31 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Security framework setup + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/init.h> +#include <linux/lsm_hooks.h> + +#include "common.h" +#include "cred.h" +#include "setup.h" + +struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { + .lbs_cred = sizeof(struct landlock_cred_security), +}; + +static int __init landlock_init(void) +{ + landlock_add_cred_hooks(); + pr_info("Up and running.\n"); + return 0; +} + +DEFINE_LSM(LANDLOCK_NAME) = { + .name = LANDLOCK_NAME, + .init = landlock_init, + .blobs = &landlock_blob_sizes, +}; diff --git a/security/landlock/setup.h b/security/landlock/setup.h new file mode 100644 index 000000000000..9fdbf33fcc33 --- /dev/null +++ b/security/landlock/setup.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Security framework setup + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_SETUP_H +#define _SECURITY_LANDLOCK_SETUP_H + +#include <linux/lsm_hooks.h> + +extern struct lsm_blob_sizes landlock_blob_sizes; + +#endif /* _SECURITY_LANDLOCK_SETUP_H */

From: Casey Schaufler casey@schaufler-ca.com

Move management of the superblock->sb_security blob out of the individual security modules and into the security infrastructure. Instead of allocating the blobs from within the modules, the modules tell the infrastructure how much space is required, and the space is allocated there.

Cc: John Johansen john.johansen@canonical.com Signed-off-by: Casey Schaufler casey@schaufler-ca.com Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Reviewed-by: Stephen Smalley stephen.smalley.work@gmail.com Acked-by: Serge Hallyn serge@hallyn.com Reviewed-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20210324191520.125779-6-mic@digikod.net ---

Changes since v30: * Add Reviewed-by Kees Cook.

Changes since v28: * Add Acked-by Serge Hallyn.

Changes since v26: * Rebase on commit b159e86b5a2a ("selinux: drop super_block backpointer from superblock_security_struct"). No change in the patch itself, only a trivial conflict because of an updated nearby line in selinux_set_mnt_opts() variable declarations.

Changes since v20: * Remove all Reviewed-by except Stephen Smalley: https://lore.kernel.org/lkml/CAEjxPJ7ARJO57MBW66=xsBzMMRb=9uLgqocK5eskHCaiVM... * Cosmetic fix in the commit message.

Changes since v17: * Rebase the original LSM stacking patch from v5.3 to v5.7: I fixed some diff conflicts caused by code moves and function renames in selinux/include/objsec.h and selinux/hooks.c . I checked that it builds but I didn't test the changes for SELinux nor SMACK. https://lore.kernel.org/r/20190829232935.7099-2-casey@schaufler-ca.com --- include/linux/lsm_hooks.h | 1 + security/security.c | 46 ++++++++++++++++++++---- security/selinux/hooks.c | 58 ++++++++++++------------------- security/selinux/include/objsec.h | 6 ++++ security/selinux/ss/services.c | 3 +- security/smack/smack.h | 6 ++++ security/smack/smack_lsm.c | 35 +++++-------------- 7 files changed, 85 insertions(+), 70 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index fb7f3193753d..75715998a95f 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -1573,6 +1573,7 @@ struct lsm_blob_sizes { int lbs_cred; int lbs_file; int lbs_inode; + int lbs_superblock; int lbs_ipc; int lbs_msg_msg; int lbs_task; diff --git a/security/security.c b/security/security.c index 5ac96b16f8fa..e9c29480eb18 100644 --- a/security/security.c +++ b/security/security.c @@ -203,6 +203,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed) lsm_set_blob_size(&needed->lbs_inode, &blob_sizes.lbs_inode); lsm_set_blob_size(&needed->lbs_ipc, &blob_sizes.lbs_ipc); lsm_set_blob_size(&needed->lbs_msg_msg, &blob_sizes.lbs_msg_msg); + lsm_set_blob_size(&needed->lbs_superblock, &blob_sizes.lbs_superblock); lsm_set_blob_size(&needed->lbs_task, &blob_sizes.lbs_task); }

@@ -333,12 +334,13 @@ static void __init ordered_lsm_init(void) for (lsm = ordered_lsms; *lsm; lsm++) prepare_lsm(*lsm);

- init_debug("cred blob size = %d\n", blob_sizes.lbs_cred); - init_debug("file blob size = %d\n", blob_sizes.lbs_file); - init_debug("inode blob size = %d\n", blob_sizes.lbs_inode); - init_debug("ipc blob size = %d\n", blob_sizes.lbs_ipc); - init_debug("msg_msg blob size = %d\n", blob_sizes.lbs_msg_msg); - init_debug("task blob size = %d\n", blob_sizes.lbs_task); + init_debug("cred blob size = %d\n", blob_sizes.lbs_cred); + init_debug("file blob size = %d\n", blob_sizes.lbs_file); + init_debug("inode blob size = %d\n", blob_sizes.lbs_inode); + init_debug("ipc blob size = %d\n", blob_sizes.lbs_ipc); + init_debug("msg_msg blob size = %d\n", blob_sizes.lbs_msg_msg); + init_debug("superblock blob size = %d\n", blob_sizes.lbs_superblock); + init_debug("task blob size = %d\n", blob_sizes.lbs_task);

/* * Create any kmem_caches needed for blobs @@ -670,6 +672,27 @@ static void __init lsm_early_task(struct task_struct *task) panic("%s: Early task alloc failed.\n", __func__); }

+/** + * lsm_superblock_alloc - allocate a composite superblock blob + * @sb: the superblock that needs a blob + * + * Allocate the superblock blob for all the modules + * + * Returns 0, or -ENOMEM if memory can't be allocated. + */ +static int lsm_superblock_alloc(struct super_block *sb) +{ + if (blob_sizes.lbs_superblock == 0) { + sb->s_security = NULL; + return 0; + } + + sb->s_security = kzalloc(blob_sizes.lbs_superblock, GFP_KERNEL); + if (sb->s_security == NULL) + return -ENOMEM; + return 0; +} + /* * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and * can be accessed with: @@ -867,12 +890,21 @@ int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *

int security_sb_alloc(struct super_block *sb) { - return call_int_hook(sb_alloc_security, 0, sb); + int rc = lsm_superblock_alloc(sb); + + if (unlikely(rc)) + return rc; + rc = call_int_hook(sb_alloc_security, 0, sb); + if (unlikely(rc)) + security_sb_free(sb); + return rc; }

void security_sb_free(struct super_block *sb) { call_void_hook(sb_free_security, sb); + kfree(sb->s_security); + sb->s_security = NULL; }

void security_free_mnt_opts(void **mnt_opts) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index ddd097790d47..2ed9c995263a 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -322,7 +322,7 @@ static void inode_free_security(struct inode *inode)

if (!isec) return; - sbsec = inode->i_sb->s_security; + sbsec = selinux_superblock(inode->i_sb); /* * As not all inode security structures are in a list, we check for * empty list outside of the lock to make sure that we won't waste @@ -340,13 +340,6 @@ static void inode_free_security(struct inode *inode) } }

-static void superblock_free_security(struct super_block *sb) -{ - struct superblock_security_struct *sbsec = sb->s_security; - sb->s_security = NULL; - kfree(sbsec); -} - struct selinux_mnt_opts { const char *fscontext, *context, *rootcontext, *defcontext; }; @@ -458,7 +451,7 @@ static int selinux_is_genfs_special_handling(struct super_block *sb)

static int selinux_is_sblabel_mnt(struct super_block *sb) { - struct superblock_security_struct *sbsec = sb->s_security; + struct superblock_security_struct *sbsec = selinux_superblock(sb);

/* * IMPORTANT: Double-check logic in this function when adding a new @@ -535,7 +528,7 @@ static int sb_check_xattr_support(struct super_block *sb)

static int sb_finish_set_opts(struct super_block *sb) { - struct superblock_security_struct *sbsec = sb->s_security; + struct superblock_security_struct *sbsec = selinux_superblock(sb); struct dentry *root = sb->s_root; struct inode *root_inode = d_backing_inode(root); int rc = 0; @@ -626,7 +619,7 @@ static int selinux_set_mnt_opts(struct super_block *sb, unsigned long *set_kern_flags) { const struct cred *cred = current_cred(); - struct superblock_security_struct *sbsec = sb->s_security; + struct superblock_security_struct *sbsec = selinux_superblock(sb); struct dentry *root = sb->s_root; struct selinux_mnt_opts *opts = mnt_opts; struct inode_security_struct *root_isec; @@ -863,8 +856,8 @@ static int selinux_set_mnt_opts(struct super_block *sb, static int selinux_cmp_sb_context(const struct super_block *oldsb, const struct super_block *newsb) { - struct superblock_security_struct *old = oldsb->s_security; - struct superblock_security_struct *new = newsb->s_security; + struct superblock_security_struct *old = selinux_superblock(oldsb); + struct superblock_security_struct *new = selinux_superblock(newsb); char oldflags = old->flags & SE_MNTMASK; char newflags = new->flags & SE_MNTMASK;

@@ -896,8 +889,9 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, unsigned long *set_kern_flags) { int rc = 0; - const struct superblock_security_struct *oldsbsec = oldsb->s_security; - struct superblock_security_struct *newsbsec = newsb->s_security; + const struct superblock_security_struct *oldsbsec = + selinux_superblock(oldsb); + struct superblock_security_struct *newsbsec = selinux_superblock(newsb);

int set_fscontext = (oldsbsec->flags & FSCONTEXT_MNT); int set_context = (oldsbsec->flags & CONTEXT_MNT); @@ -1076,7 +1070,7 @@ static int show_sid(struct seq_file *m, u32 sid)

static int selinux_sb_show_options(struct seq_file *m, struct super_block *sb) { - struct superblock_security_struct *sbsec = sb->s_security; + struct superblock_security_struct *sbsec = selinux_superblock(sb); int rc;

if (!(sbsec->flags & SE_SBINITIALIZED)) @@ -1427,7 +1421,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent if (isec->sclass == SECCLASS_FILE) isec->sclass = inode_mode_to_security_class(inode->i_mode);

- sbsec = inode->i_sb->s_security; + sbsec = selinux_superblock(inode->i_sb); if (!(sbsec->flags & SE_SBINITIALIZED)) { /* Defer initialization until selinux_complete_init, after the initial policy is loaded and the security @@ -1778,7 +1772,8 @@ selinux_determine_inode_label(const struct task_security_struct *tsec, const struct qstr *name, u16 tclass, u32 *_new_isid) { - const struct superblock_security_struct *sbsec = dir->i_sb->s_security; + const struct superblock_security_struct *sbsec = + selinux_superblock(dir->i_sb);

if ((sbsec->flags & SE_SBINITIALIZED) && (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) { @@ -1809,7 +1804,7 @@ static int may_create(struct inode *dir, int rc;

dsec = inode_security(dir); - sbsec = dir->i_sb->s_security; + sbsec = selinux_superblock(dir->i_sb);

sid = tsec->sid;

@@ -1958,7 +1953,7 @@ static int superblock_has_perm(const struct cred *cred, struct superblock_security_struct *sbsec; u32 sid = cred_sid(cred);

- sbsec = sb->s_security; + sbsec = selinux_superblock(sb); return avc_has_perm(&selinux_state, sid, sbsec->sid, SECCLASS_FILESYSTEM, perms, ad); } @@ -2587,11 +2582,7 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)

static int selinux_sb_alloc_security(struct super_block *sb) { - struct superblock_security_struct *sbsec; - - sbsec = kzalloc(sizeof(struct superblock_security_struct), GFP_KERNEL); - if (!sbsec) - return -ENOMEM; + struct superblock_security_struct *sbsec = selinux_superblock(sb);

mutex_init(&sbsec->lock); INIT_LIST_HEAD(&sbsec->isec_head); @@ -2599,16 +2590,10 @@ static int selinux_sb_alloc_security(struct super_block *sb) sbsec->sid = SECINITSID_UNLABELED; sbsec->def_sid = SECINITSID_FILE; sbsec->mntpoint_sid = SECINITSID_UNLABELED; - sb->s_security = sbsec;

return 0; }

-static void selinux_sb_free_security(struct super_block *sb) -{ - superblock_free_security(sb); -} - static inline int opt_len(const char *s) { bool open_quote = false; @@ -2687,7 +2672,7 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts) static int selinux_sb_remount(struct super_block *sb, void *mnt_opts) { struct selinux_mnt_opts *opts = mnt_opts; - struct superblock_security_struct *sbsec = sb->s_security; + struct superblock_security_struct *sbsec = selinux_superblock(sb); u32 sid; int rc;

@@ -2925,7 +2910,7 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir, int rc; char *context;

- sbsec = dir->i_sb->s_security; + sbsec = selinux_superblock(dir->i_sb);

newsid = tsec->create_sid;

@@ -3227,7 +3212,7 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns, if (!selinux_initialized(&selinux_state)) return (inode_owner_or_capable(mnt_userns, inode) ? 0 : -EPERM);

- sbsec = inode->i_sb->s_security; + sbsec = selinux_superblock(inode->i_sb); if (!(sbsec->flags & SBLABEL_MNT)) return -EOPNOTSUPP;

@@ -3472,13 +3457,14 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags) { struct inode_security_struct *isec = inode_security_novalidate(inode); - struct superblock_security_struct *sbsec = inode->i_sb->s_security; + struct superblock_security_struct *sbsec; u32 newsid; int rc;

if (strcmp(name, XATTR_SELINUX_SUFFIX)) return -EOPNOTSUPP;

+ sbsec = selinux_superblock(inode->i_sb); if (!(sbsec->flags & SBLABEL_MNT)) return -EOPNOTSUPP;

@@ -6975,6 +6961,7 @@ struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = { .lbs_inode = sizeof(struct inode_security_struct), .lbs_ipc = sizeof(struct ipc_security_struct), .lbs_msg_msg = sizeof(struct msg_security_struct), + .lbs_superblock = sizeof(struct superblock_security_struct), };

#ifdef CONFIG_PERF_EVENTS @@ -7075,7 +7062,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(bprm_committing_creds, selinux_bprm_committing_creds), LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),

- LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security), LSM_HOOK_INIT(sb_free_mnt_opts, selinux_free_mnt_opts), LSM_HOOK_INIT(sb_remount, selinux_sb_remount), LSM_HOOK_INIT(sb_kern_mount, selinux_sb_kern_mount), diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h index ca4d7ab6a835..2953132408bf 100644 --- a/security/selinux/include/objsec.h +++ b/security/selinux/include/objsec.h @@ -188,4 +188,10 @@ static inline u32 current_sid(void) return tsec->sid; }

+static inline struct superblock_security_struct *selinux_superblock( + const struct super_block *superblock) +{ + return superblock->s_security + selinux_blob_sizes.lbs_superblock; +} + #endif /* _SELINUX_OBJSEC_H_ */ diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c index 3438d0130378..9cea2e6c809f 100644 --- a/security/selinux/ss/services.c +++ b/security/selinux/ss/services.c @@ -47,6 +47,7 @@ #include <linux/sched.h> #include <linux/audit.h> #include <linux/vmalloc.h> +#include <linux/lsm_hooks.h> #include <net/netlabel.h>

#include "flask.h" @@ -2875,7 +2876,7 @@ int security_fs_use(struct selinux_state *state, struct super_block *sb) struct sidtab *sidtab; int rc = 0; struct ocontext *c; - struct superblock_security_struct *sbsec = sb->s_security; + struct superblock_security_struct *sbsec = selinux_superblock(sb); const char *fstype = sb->s_type->name;

if (!selinux_initialized(state)) { diff --git a/security/smack/smack.h b/security/smack/smack.h index a9768b12716b..7077b18c79ec 100644 --- a/security/smack/smack.h +++ b/security/smack/smack.h @@ -357,6 +357,12 @@ static inline struct smack_known **smack_ipc(const struct kern_ipc_perm *ipc) return ipc->security + smack_blob_sizes.lbs_ipc; }

+static inline struct superblock_smack *smack_superblock( + const struct super_block *superblock) +{ + return superblock->s_security + smack_blob_sizes.lbs_superblock; +} + /* * Is the directory transmuting? */ diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 12a45e61c1a5..ee3e29603c9c 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -535,12 +535,7 @@ static int smack_syslog(int typefrom_file) */ static int smack_sb_alloc_security(struct super_block *sb) { - struct superblock_smack *sbsp; - - sbsp = kzalloc(sizeof(struct superblock_smack), GFP_KERNEL); - - if (sbsp == NULL) - return -ENOMEM; + struct superblock_smack *sbsp = smack_superblock(sb);

sbsp->smk_root = &smack_known_floor; sbsp->smk_default = &smack_known_floor; @@ -549,22 +544,10 @@ static int smack_sb_alloc_security(struct super_block *sb) /* * SMK_SB_INITIALIZED will be zero from kzalloc. */ - sb->s_security = sbsp;

return 0; }

-/** - * smack_sb_free_security - free a superblock blob - * @sb: the superblock getting the blob - * - */ -static void smack_sb_free_security(struct super_block *sb) -{ - kfree(sb->s_security); - sb->s_security = NULL; -} - struct smack_mnt_opts { const char *fsdefault, *fsfloor, *fshat, *fsroot, *fstransmute; }; @@ -772,7 +755,7 @@ static int smack_set_mnt_opts(struct super_block *sb, { struct dentry *root = sb->s_root; struct inode *inode = d_backing_inode(root); - struct superblock_smack *sp = sb->s_security; + struct superblock_smack *sp = smack_superblock(sb); struct inode_smack *isp; struct smack_known *skp; struct smack_mnt_opts *opts = mnt_opts; @@ -871,7 +854,7 @@ static int smack_set_mnt_opts(struct super_block *sb, */ static int smack_sb_statfs(struct dentry *dentry) { - struct superblock_smack *sbp = dentry->d_sb->s_security; + struct superblock_smack *sbp = smack_superblock(dentry->d_sb); int rc; struct smk_audit_info ad;

@@ -905,7 +888,7 @@ static int smack_bprm_creds_for_exec(struct linux_binprm *bprm) if (isp->smk_task == NULL || isp->smk_task == bsp->smk_task) return 0;

- sbsp = inode->i_sb->s_security; + sbsp = smack_superblock(inode->i_sb); if ((sbsp->smk_flags & SMK_SB_UNTRUSTED) && isp->smk_task != sbsp->smk_root) return 0; @@ -1157,7 +1140,7 @@ static int smack_inode_rename(struct inode *old_inode, */ static int smack_inode_permission(struct inode *inode, int mask) { - struct superblock_smack *sbsp = inode->i_sb->s_security; + struct superblock_smack *sbsp = smack_superblock(inode->i_sb); struct smk_audit_info ad; int no_block = mask & MAY_NOT_BLOCK; int rc; @@ -1400,7 +1383,7 @@ static int smack_inode_removexattr(struct user_namespace *mnt_userns, */ if (strcmp(name, XATTR_NAME_SMACK) == 0) { struct super_block *sbp = dentry->d_sb; - struct superblock_smack *sbsp = sbp->s_security; + struct superblock_smack *sbsp = smack_superblock(sbp);

isp->smk_inode = sbsp->smk_default; } else if (strcmp(name, XATTR_NAME_SMACKEXEC) == 0) @@ -1670,7 +1653,7 @@ static int smack_mmap_file(struct file *file, isp = smack_inode(file_inode(file)); if (isp->smk_mmap == NULL) return 0; - sbsp = file_inode(file)->i_sb->s_security; + sbsp = smack_superblock(file_inode(file)->i_sb); if (sbsp->smk_flags & SMK_SB_UNTRUSTED && isp->smk_mmap != sbsp->smk_root) return -EACCES; @@ -3285,7 +3268,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode) return;

sbp = inode->i_sb; - sbsp = sbp->s_security; + sbsp = smack_superblock(sbp); /* * We're going to use the superblock default label * if there's no label on the file. @@ -4700,6 +4683,7 @@ struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = { .lbs_inode = sizeof(struct inode_smack), .lbs_ipc = sizeof(struct smack_known *), .lbs_msg_msg = sizeof(struct smack_known *), + .lbs_superblock = sizeof(struct superblock_smack), };

static struct security_hook_list smack_hooks[] __lsm_ro_after_init = { @@ -4711,7 +4695,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),

LSM_HOOK_INIT(sb_alloc_security, smack_sb_alloc_security), - LSM_HOOK_INIT(sb_free_security, smack_sb_free_security), LSM_HOOK_INIT(sb_free_mnt_opts, smack_free_mnt_opts), LSM_HOOK_INIT(sb_eat_lsm_opts, smack_sb_eat_lsm_opts), LSM_HOOK_INIT(sb_statfs, smack_sb_statfs),

From: Mickaël Salaün mic@linux.microsoft.com

Using Landlock objects and ruleset, it is possible to tag inodes according to a process's domain. To enable an unprivileged process to express a file hierarchy, it first needs to open a directory (or a file) and pass this file descriptor to the kernel through landlock_add_rule(2). When checking if a file access request is allowed, we walk from the requested dentry to the real root, following the different mount layers. The access to each "tagged" inodes are collected according to their rule layer level, and ANDed to create access to the requested file hierarchy. This makes possible to identify a lot of files without tagging every inodes nor modifying the filesystem, while still following the view and understanding the user has from the filesystem.

Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not keep the same struct inodes for the same inodes whereas these inodes are in use.

This commit adds a minimal set of supported filesystem access-control which doesn't enable to restrict all file-related actions. This is the result of multiple discussions to minimize the code of Landlock to ease review. Thanks to the Landlock design, extending this access-control without breaking user space will not be a problem. Moreover, seccomp filters can be used to restrict the use of syscall families which may not be currently handled by Landlock.

Cc: Al Viro viro@zeniv.linux.org.uk Cc: Anton Ivanov anton.ivanov@cambridgegreys.com Cc: James Morris jmorris@namei.org Cc: Jann Horn jannh@google.com Cc: Jeff Dike jdike@addtoit.com Cc: Kees Cook keescook@chromium.org Cc: Richard Weinberger richard@nod.at Cc: Serge E. Hallyn serge@hallyn.com Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Link: https://lore.kernel.org/r/20210324191520.125779-8-mic@digikod.net ---

Changes since v30: * Fix a (theoretical) data race in get_inode_object() (spotted by Jann Horn) and update the related comments. Also move the ihold() call to better reflect the logical order (opposite to release_inode() and hook_sb_delete()), even if it is still protected by inode->i_lock. * Improve comments related to inode and superblock management.

Changes since v29: * Remove a useless unlock/lock for the first loop walk in hook_sb_delete(). This also makes the code clearer but doesn't change the garantees for iput(). * Rename iput_inode to prev_inode, which shows its origin.

Changes since v28: * Fix race conditions that could be caused by concurrent calls to release_inode() and hook_sb_delete(). * Avoid livelock when a lot of inodes are tagged. * Improve concurrency locking and add comments to explain the specific lock rules. * Add an inode_free_security hook to check that release_inode() and hook_sb_delete() do their job. * Add early return to check_access_path() to check if the access request is empty. This doesn't change the semantic. * Reword the first description sentence (suggested by Serge Hallyn).

Changes since v27: * Fix domains with layers of non-overlapping access rights (cf. layout1.non_overlapping_accesses test) thanks to a stack of access rights per layer (replacing ORed access rights). This avoids too-restrictive domains. * Cosmetic fixes and updates in comments and Kconfig.

Changes since v26: * Check each rule of a path to enable a more permissive and pragmatic access control per layer. Suggested by Jann Horn: https://lore.kernel.org/lkml/CAG48ez1O0VTwEiRd3KqexoF78WR+cmP5bGk5Kh5Cs7aPep... * Rename check_access_path_continue() to unmask_layers() and make it return the new layer mask. * Avoid double domain check in hook_file_open(). * In the documentation, add utime(2) as another example of unhandled syscalls. Indeed, using `touch` to test write access may be tempting. * Remove outdated comment about OverlayFS. * Rename the landlock.h ifdef to align with most similar files. * Fix spelling.

Changes since v25: * Move build_check_layer() to ruleset.c, and add built-time checks for the fs_access_mask and access variables according to _LANDLOCK_ACCESS_FS_MASK. * Move limits to a dedicated file and rename them: _LANDLOCK_ACCESS_FS_LAST and _LANDLOCK_ACCESS_FS_MASK. * Set build_check_layer() as non-inline to trigger a warning if it is not called. * Use BITS_PER_TYPE() macro. * Rename function to landlock_add_fs_hooks(). * Cosmetic variable renames.

Changes since v24: * Use the new struct landlock_rule and landlock_layer to not mix accesses from different layers. Revert "Enforce deterministic interleaved path rules" from v24, and fix the layer check. This enables to follow a sane semantic: an access is granted if, for each policy layer, at least one rule encountered on the pathwalk grants the access, regardless of their position in the layer stack (suggested by Jann Horn). See layout1.interleaved_masked_accesses tests from tools/testing/selftests/landlock/fs_test.c for corner cases. * Add build-time checks for layers. * Use the new landlock_insert_rule() API.

Changes since v23: * Enforce deterministic interleaved path rules. To have consistent layered rules, granting access to a path implies that all accesses tied to inodes, from the requested file to the real root, must be checked. Otherwise, stacked rules may result to overzealous restrictions. By excluding the ability to add exceptions in the same layer (e.g. /a allowed, /a/b denied, and /a/b/c allowed), we get deterministic interleaved path rules. This removes an optimization which could be replaced by a proper cache mechanism. This also further simplifies and explain check_access_path_continue(). * Fix memory allocation error handling in landlock_create_object() calls. This prevent to inadvertently hold an inode. * In get_inode_object(), improve comments, make code more readable and move kfree() call out of the lock window. * Use the simplified landlock_insert_rule() API.

Changes since v22: * Simplify check_access_path_continue() (suggested by Jann Horn). * Remove prefetch() call for now (suggested by Jann Horn). * Fix spelling and remove superfluous comment (spotted by Jann Horn). * Cosmetic variable renaming.

Changes since v21: * Rename ARCH_EPHEMERAL_STATES to ARCH_EPHEMERAL_INODES (suggested by James Morris). * Remove the LANDLOCK_ACCESS_FS_CHROOT right because chroot(2) (which requires CAP_SYS_CHROOT) doesn't enable to bypass Landlock (as tests demonstrate it), and because it is often used by sandboxes, it would be counterproductive to forbid it. This also reduces the code size. * Clean up documentation.

Changes since v19: * Fix spelling (spotted by Randy Dunlap).

Changes since v18: * Remove useless include. * Fix spelling.

Changes since v17: * Replace landlock_release_inodes() with security_sb_delete() (requested by James Morris). * Replace struct super_block->s_landlock_inode_refs with the LSM infrastructure management of the superblock (requested by James Morris). * Fix mknod restriction with a zero mode (spotted by Vincent Dagonneau). * Minimize executed code in path_mknod and file_open hooks when the current tasks is not sandboxed. * Remove useless checks on the file pointer and inode in hook_file_open() . * Constify domain pointers. * Rename inode_landlock() to landlock_inode(). * Import include/uapi/linux/landlock.h and _LANDLOCK_ACCESS_FS_* from the ruleset and domain management patch. * Explain the rational of this minimal set of access-control. https://lore.kernel.org/lkml/f646e1c7-33cf-333f-070c-0a40ad0468cd@digikod.ne...

Changes since v16: * Add ARCH_EPHEMERAL_STATES and enable it for UML.

Changes since v15: * Replace layer_levels and layer_depth with a bitfield of layers: this enables to properly manage superset and subset of access rights, whatever their order in the stack of layers. Cf. https://lore.kernel.org/lkml/e07fe473-1801-01cc-12ae-b3167f95250e@digikod.ne... * Allow to open pipes and similar special files through /proc/self/fd/. * Properly handle internal filesystems such as nsfs: always allow these kind of roots because disconnected path cannot be evaluated. * Remove the LANDLOCK_ACCESS_FS_LINK_TO and LANDLOCK_ACCESS_FS_RENAME_{TO,FROM}, but use the LANDLOCK_ACCESS_FS_REMOVE_{FILE,DIR} and LANDLOCK_ACCESS_FS_MAKE_* instead. Indeed, it is not possible for now (and not really useful) to express the semantic of a source and a destination. * Check access rights to remove a directory or a file with rename(2). * Forbid reparenting when linking or renaming. This is needed to easily protect against possible privilege escalation by changing the place of a file or directory in relation to an enforced access policy (from the set of layers). This will be relaxed in the future. * Update hooks to take into account replacement of the object's self and beneath access bitfields with one. Simplify the code. * Check file related access rights. * Check d_is_negative() instead of !d_backing_inode() in check_access_path_continue(), and continue the path walk while there is no mapped inode e.g., with rename(2). * Check private inode in check_access_path(). * Optimize get_file_access() when dealing with a directory. * Add missing atomic.h .

Changes since v14: * Simplify the object, rule and ruleset management at the expense of a less aggressive memory freeing (contributed by Jann Horn, with additional modifications): - Rewrite release_inode() to use inode->sb->s_landlock_inode_refs. - Remove useless checks in landlock_release_inodes(), clean object pointer according to the new struct landlock_object and wait for all iput() to complete. - Rewrite get_inode_object() according to the new struct landlock_object. If there is a race-condition when cleaning up an object, we retry until the concurrent thread finished the object cleaning. Cf. https://lore.kernel.org/lkml/CAG48ez21bEn0wL1bbmTiiu8j9jP5iEWtHOwz4tURUJ+ki0... * Fix nested domains by implementing a notion of layer level and depth: - Check for matching level ranges when walking through a file path. - Only allow access if every layer granted the access request. * Handles files without mount points (e.g. pipes). * Hardens path walk by checking inode pointer values. * Prefetches d_parent when walking to the root directory. * Remove useless inode_alloc_security hook() (suggested by Jann Horn): already initialized by lsm_inode_alloc(). * Remove the inode_free_security hook. * Remove access checks that may be required for FD-only requests: truncate, getattr, lock, chmod, chown, chgrp, ioctl. This will be handle in a future evolution of Landlock, but right now the goal is to lighten the code to ease review. * Constify variables. * Move ABI checks into syscall.c . * Cosmetic variable renames.

Changes since v11: * Add back, revamp and make a fully working filesystem access-control based on paths and inodes. * Remove the eBPF dependency.

Previous changes: https://lore.kernel.org/lkml/20190721213116.23476-6-mic@digikod.net/ --- MAINTAINERS | 1 + arch/Kconfig | 7 + arch/um/Kconfig | 1 + include/uapi/linux/landlock.h | 75 ++++ security/landlock/Kconfig | 2 +- security/landlock/Makefile | 2 +- security/landlock/fs.c | 693 ++++++++++++++++++++++++++++++++++ security/landlock/fs.h | 70 ++++ security/landlock/limits.h | 4 + security/landlock/ruleset.c | 4 + security/landlock/setup.c | 7 + security/landlock/setup.h | 2 + 12 files changed, 866 insertions(+), 2 deletions(-) create mode 100644 include/uapi/linux/landlock.h create mode 100644 security/landlock/fs.c create mode 100644 security/landlock/fs.h

diff --git a/MAINTAINERS b/MAINTAINERS index 87a2738dfdec..70ec117efa8a 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -10003,6 +10003,7 @@ L: linux-security-module@vger.kernel.org S: Supported W: https://landlock.io T: git https://github.com/landlock-lsm/linux.git +F: include/uapi/linux/landlock.h F: security/landlock/ K: landlock K: LANDLOCK diff --git a/arch/Kconfig b/arch/Kconfig index ecfd3520b676..8160ab7e3e03 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1013,6 +1013,13 @@ config COMPAT_32BIT_TIME config ARCH_NO_PREEMPT bool

+config ARCH_EPHEMERAL_INODES + def_bool n + help + An arch should select this symbol if it doesn't keep track of inode + instances on its own, but instead relies on something else (e.g. the + host kernel for an UML kernel). + config ARCH_SUPPORTS_RT bool

diff --git a/arch/um/Kconfig b/arch/um/Kconfig index c3030db3325f..57cfd9a1c082 100644 --- a/arch/um/Kconfig +++ b/arch/um/Kconfig @@ -5,6 +5,7 @@ menu "UML-specific options" config UML bool default y + select ARCH_EPHEMERAL_INODES select ARCH_HAS_KCOV select ARCH_NO_PREEMPT select HAVE_ARCH_AUDITSYSCALL diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h new file mode 100644 index 000000000000..f69877099c8e --- /dev/null +++ b/include/uapi/linux/landlock.h @@ -0,0 +1,75 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +/* + * Landlock - User space API + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _UAPI_LINUX_LANDLOCK_H +#define _UAPI_LINUX_LANDLOCK_H + +/** + * DOC: fs_access + * + * A set of actions on kernel objects may be defined by an attribute (e.g. + * &struct landlock_path_beneath_attr) including a bitmask of access. + * + * Filesystem flags + * ~~~~~~~~~~~~~~~~ + * + * These flags enable to restrict a sandboxed process to a set of actions on + * files and directories. Files or directories opened before the sandboxing + * are not subject to these restrictions. + * + * A file can only receive these access rights: + * + * - %LANDLOCK_ACCESS_FS_EXECUTE: Execute a file. + * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. + * - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access. + * + * A directory can receive access rights related to files or directories. The + * following access right is applied to the directory itself, and the + * directories beneath it: + * + * - %LANDLOCK_ACCESS_FS_READ_DIR: Open a directory or list its content. + * + * However, the following access rights only apply to the content of a + * directory, not the directory itself: + * + * - %LANDLOCK_ACCESS_FS_REMOVE_DIR: Remove an empty directory or rename one. + * - %LANDLOCK_ACCESS_FS_REMOVE_FILE: Unlink (or rename) a file. + * - %LANDLOCK_ACCESS_FS_MAKE_CHAR: Create (or rename or link) a character + * device. + * - %LANDLOCK_ACCESS_FS_MAKE_DIR: Create (or rename) a directory. + * - %LANDLOCK_ACCESS_FS_MAKE_REG: Create (or rename or link) a regular file. + * - %LANDLOCK_ACCESS_FS_MAKE_SOCK: Create (or rename or link) a UNIX domain + * socket. + * - %LANDLOCK_ACCESS_FS_MAKE_FIFO: Create (or rename or link) a named pipe. + * - %LANDLOCK_ACCESS_FS_MAKE_BLOCK: Create (or rename or link) a block device. + * - %LANDLOCK_ACCESS_FS_MAKE_SYM: Create (or rename or link) a symbolic link. + * + * .. warning:: + * + * It is currently not possible to restrict some file-related actions + * accessible through these syscall families: :manpage:`chdir(2)`, + * :manpage:`truncate(2)`, :manpage:`stat(2)`, :manpage:`flock(2)`, + * :manpage:`chmod(2)`, :manpage:`chown(2)`, :manpage:`setxattr(2)`, + * :manpage:`utime(2)`, :manpage:`ioctl(2)`, :manpage:`fcntl(2)`. + * Future Landlock evolutions will enable to restrict them. + */ +#define LANDLOCK_ACCESS_FS_EXECUTE (1ULL << 0) +#define LANDLOCK_ACCESS_FS_WRITE_FILE (1ULL << 1) +#define LANDLOCK_ACCESS_FS_READ_FILE (1ULL << 2) +#define LANDLOCK_ACCESS_FS_READ_DIR (1ULL << 3) +#define LANDLOCK_ACCESS_FS_REMOVE_DIR (1ULL << 4) +#define LANDLOCK_ACCESS_FS_REMOVE_FILE (1ULL << 5) +#define LANDLOCK_ACCESS_FS_MAKE_CHAR (1ULL << 6) +#define LANDLOCK_ACCESS_FS_MAKE_DIR (1ULL << 7) +#define LANDLOCK_ACCESS_FS_MAKE_REG (1ULL << 8) +#define LANDLOCK_ACCESS_FS_MAKE_SOCK (1ULL << 9) +#define LANDLOCK_ACCESS_FS_MAKE_FIFO (1ULL << 10) +#define LANDLOCK_ACCESS_FS_MAKE_BLOCK (1ULL << 11) +#define LANDLOCK_ACCESS_FS_MAKE_SYM (1ULL << 12) + +#endif /* _UAPI_LINUX_LANDLOCK_H */ diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig index c1e862a38410..8e33c4e8ffb8 100644 --- a/security/landlock/Kconfig +++ b/security/landlock/Kconfig @@ -2,7 +2,7 @@

config SECURITY_LANDLOCK bool "Landlock support" - depends on SECURITY + depends on SECURITY && !ARCH_EPHEMERAL_INODES select SECURITY_PATH help Landlock is a sandboxing mechanism that enables processes to restrict diff --git a/security/landlock/Makefile b/security/landlock/Makefile index f1d1eb72fa76..92e3d80ab8ed 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,4 +1,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

landlock-y := setup.o object.o ruleset.o \ - cred.o ptrace.o + cred.o ptrace.o fs.o diff --git a/security/landlock/fs.c b/security/landlock/fs.c new file mode 100644 index 000000000000..3f221d0e5c90 --- /dev/null +++ b/security/landlock/fs.c @@ -0,0 +1,693 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Filesystem management and hooks + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/atomic.h> +#include <linux/bitops.h> +#include <linux/bits.h> +#include <linux/compiler_types.h> +#include <linux/dcache.h> +#include <linux/err.h> +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/limits.h> +#include <linux/list.h> +#include <linux/lsm_hooks.h> +#include <linux/mount.h> +#include <linux/namei.h> +#include <linux/path.h> +#include <linux/rcupdate.h> +#include <linux/spinlock.h> +#include <linux/stat.h> +#include <linux/types.h> +#include <linux/wait_bit.h> +#include <linux/workqueue.h> +#include <uapi/linux/landlock.h> + +#include "common.h" +#include "cred.h" +#include "fs.h" +#include "limits.h" +#include "object.h" +#include "ruleset.h" +#include "setup.h" + +/* Underlying object management */ + +static void release_inode(struct landlock_object *const object) + __releases(object->lock) +{ + struct inode *const inode = object->underobj; + struct super_block *sb; + + if (!inode) { + spin_unlock(&object->lock); + return; + } + + /* + * Protects against concurrent use by hook_sb_delete() of the reference + * to the underlying inode. + */ + object->underobj = NULL; + /* + * Makes sure that if the filesystem is concurrently unmounted, + * hook_sb_delete() will wait for us to finish iput(). + */ + sb = inode->i_sb; + atomic_long_inc(&landlock_superblock(sb)->inode_refs); + spin_unlock(&object->lock); + /* + * Because object->underobj was not NULL, hook_sb_delete() and + * get_inode_object() guarantee that it is safe to reset + * landlock_inode(inode)->object while it is not NULL. It is therefore + * not necessary to lock inode->i_lock. + */ + rcu_assign_pointer(landlock_inode(inode)->object, NULL); + /* + * Now, new rules can safely be tied to @inode with get_inode_object(). + */ + + iput(inode); + if (atomic_long_dec_and_test(&landlock_superblock(sb)->inode_refs)) + wake_up_var(&landlock_superblock(sb)->inode_refs); +} + +static const struct landlock_object_underops landlock_fs_underops = { + .release = release_inode +}; + +/* Ruleset management */ + +static struct landlock_object *get_inode_object(struct inode *const inode) +{ + struct landlock_object *object, *new_object; + struct landlock_inode_security *inode_sec = landlock_inode(inode); + + rcu_read_lock(); +retry: + object = rcu_dereference(inode_sec->object); + if (object) { + if (likely(refcount_inc_not_zero(&object->usage))) { + rcu_read_unlock(); + return object; + } + /* + * We are racing with release_inode(), the object is going + * away. Wait for release_inode(), then retry. + */ + spin_lock(&object->lock); + spin_unlock(&object->lock); + goto retry; + } + rcu_read_unlock(); + + /* + * If there is no object tied to @inode, then create a new one (without + * holding any locks). + */ + new_object = landlock_create_object(&landlock_fs_underops, inode); + if (IS_ERR(new_object)) + return new_object; + + /* + * Protects against concurrent calls to get_inode_object() or + * hook_sb_delete(). + */ + spin_lock(&inode->i_lock); + if (unlikely(rcu_access_pointer(inode_sec->object))) { + /* Someone else just created the object, bail out and retry. */ + spin_unlock(&inode->i_lock); + kfree(new_object); + + rcu_read_lock(); + goto retry; + } + + /* + * @inode will be released by hook_sb_delete() on its superblock + * shutdown, or by release_inode() when no more ruleset references the + * related object. + */ + ihold(inode); + rcu_assign_pointer(inode_sec->object, new_object); + spin_unlock(&inode->i_lock); + return new_object; +} + +/* All access rights that can be tied to files. */ +#define ACCESS_FILE ( \ + LANDLOCK_ACCESS_FS_EXECUTE | \ + LANDLOCK_ACCESS_FS_WRITE_FILE | \ + LANDLOCK_ACCESS_FS_READ_FILE) + +/* + * @path: Should have been checked by get_path_from_fd(). + */ +int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, + const struct path *const path, u32 access_rights) +{ + int err; + struct landlock_object *object; + + /* Files only get access rights that make sense. */ + if (!d_is_dir(path->dentry) && (access_rights | ACCESS_FILE) != + ACCESS_FILE) + return -EINVAL; + if (WARN_ON_ONCE(ruleset->num_layers != 1)) + return -EINVAL; + + /* Transforms relative access rights to absolute ones. */ + access_rights |= LANDLOCK_MASK_ACCESS_FS & ~ruleset->fs_access_masks[0]; + object = get_inode_object(d_backing_inode(path->dentry)); + if (IS_ERR(object)) + return PTR_ERR(object); + mutex_lock(&ruleset->lock); + err = landlock_insert_rule(ruleset, object, access_rights); + mutex_unlock(&ruleset->lock); + /* + * No need to check for an error because landlock_insert_rule() + * increments the refcount for the new object if needed. + */ + landlock_put_object(object); + return err; +} + +/* Access-control management */ + +static inline u64 unmask_layers( + const struct landlock_ruleset *const domain, + const struct path *const path, const u32 access_request, + u64 layer_mask) +{ + const struct landlock_rule *rule; + const struct inode *inode; + size_t i; + + if (d_is_negative(path->dentry)) + /* Continues to walk while there is no mapped inode. */ + return layer_mask; + inode = d_backing_inode(path->dentry); + rcu_read_lock(); + rule = landlock_find_rule(domain, + rcu_dereference(landlock_inode(inode)->object)); + rcu_read_unlock(); + if (!rule) + return layer_mask; + + /* + * An access is granted if, for each policy layer, at least one rule + * encountered on the pathwalk grants the requested accesses, + * regardless of their position in the layer stack. We must then check + * the remaining layers for each inode, from the first added layer to + * the last one. + */ + for (i = 0; i < rule->num_layers; i++) { + const struct landlock_layer *const layer = &rule->layers[i]; + const u64 layer_level = BIT_ULL(layer->level - 1); + + /* Checks that the layer grants access to the full request. */ + if ((layer->access & access_request) == access_request) { + layer_mask &= ~layer_level; + + if (layer_mask == 0) + return layer_mask; + } + } + return layer_mask; +} + +static int check_access_path(const struct landlock_ruleset *const domain, + const struct path *const path, u32 access_request) +{ + bool allowed = false; + struct path walker_path; + u64 layer_mask; + size_t i; + + /* Make sure all layers can be checked. */ + BUILD_BUG_ON(BITS_PER_TYPE(layer_mask) < LANDLOCK_MAX_NUM_LAYERS); + + if (!access_request) + return 0; + if (WARN_ON_ONCE(!domain || !path)) + return 0; + /* + * Allows access to pseudo filesystems that will never be mountable + * (e.g. sockfs, pipefs), but can still be reachable through + * /proc/<pid>/fd/<file-descriptor> . + */ + if ((path->dentry->d_sb->s_flags & SB_NOUSER) || + (d_is_positive(path->dentry) && + unlikely(IS_PRIVATE(d_backing_inode(path->dentry))))) + return 0; + if (WARN_ON_ONCE(domain->num_layers < 1)) + return -EACCES; + + /* Saves all layers handling a subset of requested accesses. */ + layer_mask = 0; + for (i = 0; i < domain->num_layers; i++) { + if (domain->fs_access_masks[i] & access_request) + layer_mask |= BIT_ULL(i); + } + /* An access request not handled by the domain is allowed. */ + if (layer_mask == 0) + return 0; + + walker_path = *path; + path_get(&walker_path); + /* + * We need to walk through all the hierarchy to not miss any relevant + * restriction. + */ + while (true) { + struct dentry *parent_dentry; + + layer_mask = unmask_layers(domain, &walker_path, + access_request, layer_mask); + if (layer_mask == 0) { + /* Stops when a rule from each layer grants access. */ + allowed = true; + break; + } + +jump_up: + if (walker_path.dentry == walker_path.mnt->mnt_root) { + if (follow_up(&walker_path)) { + /* Ignores hidden mount points. */ + goto jump_up; + } else { + /* + * Stops at the real root. Denies access + * because not all layers have granted access. + */ + allowed = false; + break; + } + } + if (unlikely(IS_ROOT(walker_path.dentry))) { + /* + * Stops at disconnected root directories. Only allows + * access to internal filesystems (e.g. nsfs, which is + * reachable through /proc/<pid>/ns/<namespace>). + */ + allowed = !!(walker_path.mnt->mnt_flags & MNT_INTERNAL); + break; + } + parent_dentry = dget_parent(walker_path.dentry); + dput(walker_path.dentry); + walker_path.dentry = parent_dentry; + } + path_put(&walker_path); + return allowed ? 0 : -EACCES; +} + +static inline int current_check_access_path(const struct path *const path, + const u32 access_request) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + return check_access_path(dom, path, access_request); +} + +/* Inode hooks */ + +static void hook_inode_free_security(struct inode *const inode) +{ + /* + * All inodes must already have been untied from their object by + * release_inode() or hook_sb_delete(). + */ + WARN_ON_ONCE(landlock_inode(inode)->object); +} + +/* Super-block hooks */ + +/* + * Release the inodes used in a security policy. + * + * Cf. fsnotify_unmount_inodes() and invalidate_inodes() + */ +static void hook_sb_delete(struct super_block *const sb) +{ + struct inode *inode, *prev_inode = NULL; + + if (!landlock_initialized) + return; + + spin_lock(&sb->s_inode_list_lock); + list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { + struct landlock_object *object; + + /* Only handles referenced inodes. */ + if (!atomic_read(&inode->i_count)) + continue; + + /* + * Protects against concurrent modification of inode (e.g. + * from get_inode_object()). + */ + spin_lock(&inode->i_lock); + /* + * Checks I_FREEING and I_WILL_FREE to protect against a race + * condition when release_inode() just called iput(), which + * could lead to a NULL dereference of inode->security or a + * second call to iput() for the same Landlock object. Also + * checks I_NEW because such inode cannot be tied to an object. + */ + if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) { + spin_unlock(&inode->i_lock); + continue; + } + + rcu_read_lock(); + object = rcu_dereference(landlock_inode(inode)->object); + if (!object) { + rcu_read_unlock(); + spin_unlock(&inode->i_lock); + continue; + } + /* Keeps a reference to this inode until the next loop walk. */ + __iget(inode); + spin_unlock(&inode->i_lock); + + /* + * If there is no concurrent release_inode() ongoing, then we + * are in charge of calling iput() on this inode, otherwise we + * will just wait for it to finish. + */ + spin_lock(&object->lock); + if (object->underobj == inode) { + object->underobj = NULL; + spin_unlock(&object->lock); + rcu_read_unlock(); + + /* + * Because object->underobj was not NULL, + * release_inode() and get_inode_object() guarantee + * that it is safe to reset + * landlock_inode(inode)->object while it is not NULL. + * It is therefore not necessary to lock inode->i_lock. + */ + rcu_assign_pointer(landlock_inode(inode)->object, NULL); + /* + * At this point, we own the ihold() reference that was + * originally set up by get_inode_object() and the + * __iget() reference that we just set in this loop + * walk. Therefore the following call to iput() will + * not sleep nor drop the inode because there is now at + * least two references to it. + */ + iput(inode); + } else { + spin_unlock(&object->lock); + rcu_read_unlock(); + } + + if (prev_inode) { + /* + * At this point, we still own the __iget() reference + * that we just set in this loop walk. Therefore we + * can drop the list lock and know that the inode won't + * disappear from under us until the next loop walk. + */ + spin_unlock(&sb->s_inode_list_lock); + /* + * We can now actually put the inode reference from the + * previous loop walk, which is not needed anymore. + */ + iput(prev_inode); + cond_resched(); + spin_lock(&sb->s_inode_list_lock); + } + prev_inode = inode; + } + spin_unlock(&sb->s_inode_list_lock); + + /* Puts the inode reference from the last loop walk, if any. */ + if (prev_inode) + iput(prev_inode); + /* Waits for pending iput() in release_inode(). */ + wait_var_event(&landlock_superblock(sb)->inode_refs, !atomic_long_read( + &landlock_superblock(sb)->inode_refs)); +} + +/* + * Because a Landlock security policy is defined according to the filesystem + * layout (i.e. the mount namespace), changing it may grant access to files not + * previously allowed. + * + * To make it simple, deny any filesystem layout modification by landlocked + * processes. Non-landlocked processes may still change the namespace of a + * landlocked process, but this kind of threat must be handled by a system-wide + * access-control security policy. + * + * This could be lifted in the future if Landlock can safely handle mount + * namespace updates requested by a landlocked process. Indeed, we could + * update the current domain (which is currently read-only) by taking into + * account the accesses of the source and the destination of a new mount point. + * However, it would also require to make all the child domains dynamically + * inherit these new constraints. Anyway, for backward compatibility reasons, + * a dedicated user space option would be required (e.g. as a ruleset command + * option). + */ +static int hook_sb_mount(const char *const dev_name, + const struct path *const path, const char *const type, + const unsigned long flags, void *const data) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +static int hook_move_mount(const struct path *const from_path, + const struct path *const to_path) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* + * Removing a mount point may reveal a previously hidden file hierarchy, which + * may then grant access to files, which may have previously been forbidden. + */ +static int hook_sb_umount(struct vfsmount *const mnt, const int flags) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* + * pivot_root(2), like mount(2), changes the current mount namespace. It must + * then be forbidden for a landlocked process. + * + * However, chroot(2) may be allowed because it only changes the relative root + * directory of the current process. Moreover, it can be used to restrict the + * view of the filesystem. + */ +static int hook_sb_pivotroot(const struct path *const old_path, + const struct path *const new_path) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* Path hooks */ + +static inline u32 get_mode_access(const umode_t mode) +{ + switch (mode & S_IFMT) { + case S_IFLNK: + return LANDLOCK_ACCESS_FS_MAKE_SYM; + case 0: + /* A zero mode translates to S_IFREG. */ + case S_IFREG: + return LANDLOCK_ACCESS_FS_MAKE_REG; + case S_IFDIR: + return LANDLOCK_ACCESS_FS_MAKE_DIR; + case S_IFCHR: + return LANDLOCK_ACCESS_FS_MAKE_CHAR; + case S_IFBLK: + return LANDLOCK_ACCESS_FS_MAKE_BLOCK; + case S_IFIFO: + return LANDLOCK_ACCESS_FS_MAKE_FIFO; + case S_IFSOCK: + return LANDLOCK_ACCESS_FS_MAKE_SOCK; + default: + WARN_ON_ONCE(1); + return 0; + } +} + +/* + * Creating multiple links or renaming may lead to privilege escalations if not + * handled properly. Indeed, we must be sure that the source doesn't gain more + * privileges by being accessible from the destination. This is getting more + * complex when dealing with multiple layers. The whole picture can be seen as + * a multilayer partial ordering problem. A future version of Landlock will + * deal with that. + */ +static int hook_path_link(struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + /* The mount points are the same for old and new paths, cf. EXDEV. */ + if (old_dentry->d_parent != new_dir->dentry) + /* For now, forbids reparenting. */ + return -EACCES; + if (unlikely(d_is_negative(old_dentry))) + return -EACCES; + return check_access_path(dom, new_dir, + get_mode_access(d_backing_inode(old_dentry)->i_mode)); +} + +static inline u32 maybe_remove(const struct dentry *const dentry) +{ + if (d_is_negative(dentry)) + return 0; + return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR : + LANDLOCK_ACCESS_FS_REMOVE_FILE; +} + +static int hook_path_rename(const struct path *const old_dir, + struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + /* The mount points are the same for old and new paths, cf. EXDEV. */ + if (old_dir->dentry != new_dir->dentry) + /* For now, forbids reparenting. */ + return -EACCES; + if (WARN_ON_ONCE(d_is_negative(old_dentry))) + return -EACCES; + /* RENAME_EXCHANGE is handled because directories are the same. */ + return check_access_path(dom, old_dir, maybe_remove(old_dentry) | + maybe_remove(new_dentry) | + get_mode_access(d_backing_inode(old_dentry)->i_mode)); +} + +static int hook_path_mkdir(const struct path *const dir, + struct dentry *const dentry, const umode_t mode) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR); +} + +static int hook_path_mknod(const struct path *const dir, + struct dentry *const dentry, const umode_t mode, + const unsigned int dev) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + return check_access_path(dom, dir, get_mode_access(mode)); +} + +static int hook_path_symlink(const struct path *const dir, + struct dentry *const dentry, const char *const old_name) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM); +} + +static int hook_path_unlink(const struct path *const dir, + struct dentry *const dentry) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE); +} + +static int hook_path_rmdir(const struct path *const dir, + struct dentry *const dentry) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR); +} + +/* File hooks */ + +static inline u32 get_file_access(const struct file *const file) +{ + u32 access = 0; + + if (file->f_mode & FMODE_READ) { + /* A directory can only be opened in read mode. */ + if (S_ISDIR(file_inode(file)->i_mode)) + return LANDLOCK_ACCESS_FS_READ_DIR; + access = LANDLOCK_ACCESS_FS_READ_FILE; + } + if (file->f_mode & FMODE_WRITE) + access |= LANDLOCK_ACCESS_FS_WRITE_FILE; + /* __FMODE_EXEC is indeed part of f_flags, not f_mode. */ + if (file->f_flags & __FMODE_EXEC) + access |= LANDLOCK_ACCESS_FS_EXECUTE; + return access; +} + +static int hook_file_open(struct file *const file) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + /* + * Because a file may be opened with O_PATH, get_file_access() may + * return 0. This case will be handled with a future Landlock + * evolution. + */ + return check_access_path(dom, &file->f_path, get_file_access(file)); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(inode_free_security, hook_inode_free_security), + + LSM_HOOK_INIT(sb_delete, hook_sb_delete), + LSM_HOOK_INIT(sb_mount, hook_sb_mount), + LSM_HOOK_INIT(move_mount, hook_move_mount), + LSM_HOOK_INIT(sb_umount, hook_sb_umount), + LSM_HOOK_INIT(sb_remount, hook_sb_remount), + LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot), + + LSM_HOOK_INIT(path_link, hook_path_link), + LSM_HOOK_INIT(path_rename, hook_path_rename), + LSM_HOOK_INIT(path_mkdir, hook_path_mkdir), + LSM_HOOK_INIT(path_mknod, hook_path_mknod), + LSM_HOOK_INIT(path_symlink, hook_path_symlink), + LSM_HOOK_INIT(path_unlink, hook_path_unlink), + LSM_HOOK_INIT(path_rmdir, hook_path_rmdir), + + LSM_HOOK_INIT(file_open, hook_file_open), +}; + +__init void landlock_add_fs_hooks(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/fs.h b/security/landlock/fs.h new file mode 100644 index 000000000000..187284b421c9 --- /dev/null +++ b/security/landlock/fs.h @@ -0,0 +1,70 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Filesystem management and hooks + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_FS_H +#define _SECURITY_LANDLOCK_FS_H + +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/rcupdate.h> + +#include "ruleset.h" +#include "setup.h" + +/** + * struct landlock_inode_security - Inode security blob + * + * Enable to reference a &struct landlock_object tied to an inode (i.e. + * underlying object). + */ +struct landlock_inode_security { + /** + * @object: Weak pointer to an allocated object. All assignments of a + * new object are protected by the underlying inode->i_lock. However, + * atomically disassociating @object from the inode is only protected + * by @object->lock, from the time @object's usage refcount drops to + * zero to the time this pointer is nulled out (cf. release_inode() and + * hook_sb_delete()). Indeed, such disassociation doesn't require + * inode->i_lock thanks to the careful rcu_access_pointer() check + * performed by get_inode_object(). + */ + struct landlock_object __rcu *object; +}; + +/** + * struct landlock_superblock_security - Superblock security blob + * + * Enable hook_sb_delete() to wait for concurrent calls to release_inode(). + */ +struct landlock_superblock_security { + /** + * @inode_refs: Number of pending inodes (from this superblock) that + * are being released by release_inode(). + * Cf. struct super_block->s_fsnotify_inode_refs . + */ + atomic_long_t inode_refs; +}; + +static inline struct landlock_inode_security *landlock_inode( + const struct inode *const inode) +{ + return inode->i_security + landlock_blob_sizes.lbs_inode; +} + +static inline struct landlock_superblock_security *landlock_superblock( + const struct super_block *const superblock) +{ + return superblock->s_security + landlock_blob_sizes.lbs_superblock; +} + +__init void landlock_add_fs_hooks(void); + +int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, + const struct path *const path, u32 access_hierarchy); + +#endif /* _SECURITY_LANDLOCK_FS_H */ diff --git a/security/landlock/limits.h b/security/landlock/limits.h index b734f597bb0e..2a0a1095ee27 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -10,8 +10,12 @@ #define _SECURITY_LANDLOCK_LIMITS_H

#include <linux/limits.h> +#include <uapi/linux/landlock.h>

#define LANDLOCK_MAX_NUM_LAYERS 64 #define LANDLOCK_MAX_NUM_RULES U32_MAX

+#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_MAKE_SYM +#define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1) + #endif /* _SECURITY_LANDLOCK_LIMITS_H */ diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c index 2e616f6d5274..ec72b9262bf3 100644 --- a/security/landlock/ruleset.c +++ b/security/landlock/ruleset.c @@ -116,9 +116,11 @@ static void build_check_ruleset(void) .num_rules = ~0, .num_layers = ~0, }; + typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;

BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES); BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS); + BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS); }

/** @@ -217,9 +219,11 @@ static void build_check_layer(void) { const struct landlock_layer layer = { .level = ~0, + .access = ~0, };

BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS); + BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS); }

/* @ruleset must be locked by the caller. */ diff --git a/security/landlock/setup.c b/security/landlock/setup.c index a5d6ef334991..f8e8e980454c 100644 --- a/security/landlock/setup.c +++ b/security/landlock/setup.c @@ -11,17 +11,24 @@

#include "common.h" #include "cred.h" +#include "fs.h" #include "ptrace.h" #include "setup.h"

+bool landlock_initialized __lsm_ro_after_init = false; + struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { .lbs_cred = sizeof(struct landlock_cred_security), + .lbs_inode = sizeof(struct landlock_inode_security), + .lbs_superblock = sizeof(struct landlock_superblock_security), };

static int __init landlock_init(void) { landlock_add_cred_hooks(); landlock_add_ptrace_hooks(); + landlock_add_fs_hooks(); + landlock_initialized = true; pr_info("Up and running.\n"); return 0; } diff --git a/security/landlock/setup.h b/security/landlock/setup.h index 9fdbf33fcc33..1daffab1ab4b 100644 --- a/security/landlock/setup.h +++ b/security/landlock/setup.h @@ -11,6 +11,8 @@

#include <linux/lsm_hooks.h>

+extern bool landlock_initialized; + extern struct lsm_blob_sizes landlock_blob_sizes;

#endif /* _SECURITY_LANDLOCK_SETUP_H */

From: Mickaël Salaün mic@linux.microsoft.com

Wire up the following system calls for all architectures: * landlock_create_ruleset(2) * landlock_add_rule(2) * landlock_restrict_self(2)

Cc: Arnd Bergmann arnd@arndb.de Cc: James Morris jmorris@namei.org Cc: Jann Horn jannh@google.com Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Link: https://lore.kernel.org/r/20210324191520.125779-10-mic@digikod.net ---

Changes since v30: * Increase syscall numbers to leave space for quotactl_path(2): synchronize with Landlock syscalls in -next.

Changes since v29: * Rebase on v5.12-rc3 and fix trivial conflict with mount_setattr(2). * Synchronize syscall numbers with -next, which are the same as for v5.12-rc3.

Changes since v27: * Rename landlock_enforce_ruleset_self(2) to landlock_restrict_self(2). * Cosmetic fix: align TBL enries.

Changes since v26: * Rename landlock_enforce_ruleset_current(2) to landlock_enforce_ruleset_self(2).

Changes since v25: * Rebase and leave space for the new epoll_pwait2(2) and memfd_secret(2) from -next.

Changes since v21: * Rebase and leave space for watch_mount(2) from -next.

Changes since v20: * Remove landlock_get_features(2). * Decrease syscall numbers to stick to process_madvise(2) in -next. * Rename landlock_enforce_ruleset(2) to landlock_enforce_ruleset_current(2).

Changes since v19: * Increase syscall numbers by 4 to leave space for new ones (in linux-next): watch_mount(2), watch_sb(2), fsinfo(2) and process_madvise(2) (requested by Arnd Bergmann). * Replace the previous multiplexor landlock(2) with 4 syscalls: landlock_get_features(2), landlock_create_ruleset(2), landlock_add_rule(2) and landlock_enforce_ruleset(2).

Changes since v18: * Increase the syscall number because of the new faccessat2(2).

Changes since v14: * Add all architectures.

Changes since v13: * New implementation. --- arch/alpha/kernel/syscalls/syscall.tbl | 3 +++ arch/arm/tools/syscall.tbl | 3 +++ arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 6 ++++++ arch/ia64/kernel/syscalls/syscall.tbl | 3 +++ arch/m68k/kernel/syscalls/syscall.tbl | 3 +++ arch/microblaze/kernel/syscalls/syscall.tbl | 3 +++ arch/mips/kernel/syscalls/syscall_n32.tbl | 3 +++ arch/mips/kernel/syscalls/syscall_n64.tbl | 3 +++ arch/mips/kernel/syscalls/syscall_o32.tbl | 3 +++ arch/parisc/kernel/syscalls/syscall.tbl | 3 +++ arch/powerpc/kernel/syscalls/syscall.tbl | 3 +++ arch/s390/kernel/syscalls/syscall.tbl | 3 +++ arch/sh/kernel/syscalls/syscall.tbl | 3 +++ arch/sparc/kernel/syscalls/syscall.tbl | 3 +++ arch/x86/entry/syscalls/syscall_32.tbl | 3 +++ arch/x86/entry/syscalls/syscall_64.tbl | 3 +++ arch/xtensa/kernel/syscalls/syscall.tbl | 3 +++ include/uapi/asm-generic/unistd.h | 8 +++++++- 19 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 02f0244e005c..4240f21b10b3 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -482,3 +482,6 @@ 550 common process_madvise sys_process_madvise 551 common epoll_pwait2 sys_epoll_pwait2 552 common mount_setattr sys_mount_setattr +554 common landlock_create_ruleset sys_landlock_create_ruleset +555 common landlock_add_rule sys_landlock_add_rule +556 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index dcc1191291a2..161423a5d773 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -456,3 +456,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index 949788f5ba40..727bfc3be99b 100644 --- a/arch/arm64/include/asm/unistd.h +++ b/arch/arm64/include/asm/unistd.h @@ -38,7 +38,7 @@ #define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5) #define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)

-#define __NR_compat_syscalls 443 +#define __NR_compat_syscalls 447 #endif

#define __ARCH_WANT_SYS_CLONE diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index 3d874f624056..fdfe06bae3fc 100644 --- a/arch/arm64/include/asm/unistd32.h +++ b/arch/arm64/include/asm/unistd32.h @@ -893,6 +893,12 @@ __SYSCALL(__NR_process_madvise, sys_process_madvise) __SYSCALL(__NR_epoll_pwait2, compat_sys_epoll_pwait2) #define __NR_mount_setattr 442 __SYSCALL(__NR_mount_setattr, sys_mount_setattr) +#define __NR_landlock_create_ruleset 444 +__SYSCALL(__NR_landlock_create_ruleset, sys_landlock_create_ruleset) +#define __NR_landlock_add_rule 445 +__SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule) +#define __NR_landlock_restrict_self 446 +__SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)

/* * Please add new compat syscalls above this comment and update diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl index d89231166e19..48dbbc95a01f 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -363,3 +363,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index 72bde6707dd3..595108bbbe42 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -442,3 +442,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index d603a5ec9338..db23d65871f9 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -448,3 +448,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl index 8fd8c1790941..5028839225fa 100644 --- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl @@ -381,3 +381,6 @@ 440 n32 process_madvise sys_process_madvise 441 n32 epoll_pwait2 compat_sys_epoll_pwait2 442 n32 mount_setattr sys_mount_setattr +444 n32 landlock_create_ruleset sys_landlock_create_ruleset +445 n32 landlock_add_rule sys_landlock_add_rule +446 n32 landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl index 169f21438065..ec9c68b75e23 100644 --- a/arch/mips/kernel/syscalls/syscall_n64.tbl +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl @@ -357,3 +357,6 @@ 440 n64 process_madvise sys_process_madvise 441 n64 epoll_pwait2 sys_epoll_pwait2 442 n64 mount_setattr sys_mount_setattr +444 n64 landlock_create_ruleset sys_landlock_create_ruleset +445 n64 landlock_add_rule sys_landlock_add_rule +446 n64 landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl index 090d29ca80ff..24afd33e3e49 100644 --- a/arch/mips/kernel/syscalls/syscall_o32.tbl +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl @@ -430,3 +430,6 @@ 440 o32 process_madvise sys_process_madvise 441 o32 epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 o32 mount_setattr sys_mount_setattr +444 o32 landlock_create_ruleset sys_landlock_create_ruleset +445 o32 landlock_add_rule sys_landlock_add_rule +446 o32 landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 271a92519683..8ddd0b82d767 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -440,3 +440,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 0b2480cf3e47..02150894b1cf 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -522,3 +522,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index 3abef2144dac..331663efd3e7 100644 --- a/arch/s390/kernel/syscalls/syscall.tbl +++ b/arch/s390/kernel/syscalls/syscall.tbl @@ -445,3 +445,6 @@ 440 common process_madvise sys_process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl index d08eebad6b7f..6ada711f4b72 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -445,3 +445,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index 84403a99039c..1dbe3239a638 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -488,3 +488,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index a1c9f496fca6..782c310de1da 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -447,3 +447,6 @@ 440 i386 process_madvise sys_process_madvise 441 i386 epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 i386 mount_setattr sys_mount_setattr +444 i386 landlock_create_ruleset sys_landlock_create_ruleset +445 i386 landlock_add_rule sys_landlock_add_rule +446 i386 landlock_restrict_self sys_landlock_restrict_self diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 7bf01cbe582f..8604ee4bfff9 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -364,6 +364,9 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self

# # Due to a historical design error, certain syscalls are numbered differently diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl index 365a9b849224..2fad056a32e8 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -413,3 +413,6 @@ 440 common process_madvise sys_process_madvise 441 common epoll_pwait2 sys_epoll_pwait2 442 common mount_setattr sys_mount_setattr +444 common landlock_create_ruleset sys_landlock_create_ruleset +445 common landlock_add_rule sys_landlock_add_rule +446 common landlock_restrict_self sys_landlock_restrict_self diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index ce58cff99b66..300608b05226 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -863,9 +863,15 @@ __SYSCALL(__NR_process_madvise, sys_process_madvise) __SC_COMP(__NR_epoll_pwait2, sys_epoll_pwait2, compat_sys_epoll_pwait2) #define __NR_mount_setattr 442 __SYSCALL(__NR_mount_setattr, sys_mount_setattr) +#define __NR_landlock_create_ruleset 444 +__SYSCALL(__NR_landlock_create_ruleset, sys_landlock_create_ruleset) +#define __NR_landlock_add_rule 445 +__SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule) +#define __NR_landlock_restrict_self 446 +__SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)

#undef __NR_syscalls -#define __NR_syscalls 443 +#define __NR_syscalls 447

/* * 32 bit systems traditionally used different

From: Mickaël Salaün mic@linux.microsoft.com

Add a first document describing userspace API: how to define and enforce a Landlock security policy. This is explained with a simple example. The Landlock system calls are described with their expected behavior and current limitations.

Another document is dedicated to kernel developers, describing guiding principles and some important kernel structures.

This documentation can be built with the Sphinx framework.

Cc: James Morris jmorris@namei.org Cc: Jann Horn jannh@google.com Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Reviewed-by: Vincent Dagonneau vincent.dagonneau@ssi.gouv.fr Link: https://lore.kernel.org/r/20210324191520.125779-13-mic@digikod.net ---

Changes since v30: * Fix typo (spotted by Kees Cook). * Extend commit description (suggested by Kees Cook). * Add note about what a Landlock user should do about OverlayFS (requested by Kees Cook). * Include inode and superblock documentation. * Improve explanations about special filesystem limitations, and highlight automatic /proc restrictions. * Bump the last modification date.

Changes since v28: * Reorder subsections by importance in the "Current limitations" section.

Changes since v27: * Update landlock_restrict_self(2). * Update date and copyright.

Changes since v25: * Explain the behavior of layered access rights. * Explain how bind mounts and overayfs mounts are handled by Landlock: merged overlayfs mount points have their own inodes, which makes these hierarchies independent from its upper and lower layers, unlike bind mounts which share the same inodes between the source hierarchy and the mount point hierarchy. New overlayfs mount and bind mount tests check these behaviors. * Synchronize with the new syscalls.c file and update syscall names. * Fix spelling. * Remove Reviewed-by Jann Horn because of the above changes.

Changes since v24: * Add Reviewed-by Jann Horn. * Add a paragraph to explain how the ruleset layers work. * Bump date.

Changes since v23: * Explain limitations for the maximum number of stacked ruleset, and the memory usage restrictions.

Changes since v22: * Fix spelling and remove obsolete sentence (spotted by Jann Horn). * Bump date.

Changes since v21: * Move the user space documentation to userspace-api/landlock.rst and the kernel documentation to security/landlock.rst . * Add license headers. * Add last update dates. * Update MAINTAINERS file. * Add (back) links to git.kernel.org . * Fix spelling.

Changes since v20: * Update examples and documentation with the new syscalls.

Changes since v19: * Update examples and documentation with the new syscalls.

Changes since v15: * Add current limitations.

Changes since v14: * Fix spelling (contributed by Randy Dunlap). * Extend documentation about inheritance and explain layer levels. * Remove the use of now-removed access rights. * Use GitHub links. * Improve kernel documentation. * Add section for tests. * Update example.

Changes since v13: * Rewrote the documentation according to the major revamp.

Previous changes: https://lore.kernel.org/lkml/20191104172146.30797-8-mic@digikod.net/ --- Documentation/security/index.rst | 1 + Documentation/security/landlock.rst | 85 +++++++ Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/landlock.rst | 311 +++++++++++++++++++++++ MAINTAINERS | 2 + 5 files changed, 400 insertions(+) create mode 100644 Documentation/security/landlock.rst create mode 100644 Documentation/userspace-api/landlock.rst

diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst index 8129405eb2cc..16335de04e8c 100644 --- a/Documentation/security/index.rst +++ b/Documentation/security/index.rst @@ -16,3 +16,4 @@ Security Documentation siphash tpm/index digsig + landlock diff --git a/Documentation/security/landlock.rst b/Documentation/security/landlock.rst new file mode 100644 index 000000000000..2e84925ae971 --- /dev/null +++ b/Documentation/security/landlock.rst @@ -0,0 +1,85 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2017-2020 Mickaël Salaün mic@digikod.net +.. Copyright © 2019-2020 ANSSI + +================================== +Landlock LSM: kernel documentation +================================== + +:Author: Mickaël Salaün +:Date: March 2021 + +Landlock's goal is to create scoped access-control (i.e. sandboxing). To +harden a whole system, this feature should be available to any process, +including unprivileged ones. Because such process may be compromised or +backdoored (i.e. untrusted), Landlock's features must be safe to use from the +kernel and other processes point of view. Landlock's interface must therefore +expose a minimal attack surface. + +Landlock is designed to be usable by unprivileged processes while following the +system security policy enforced by other access control mechanisms (e.g. DAC, +LSM). Indeed, a Landlock rule shall not interfere with other access-controls +enforced on the system, only add more restrictions. + +Any user can enforce Landlock rulesets on their processes. They are merged and +evaluated according to the inherited ones in a way that ensures that only more +constraints can be added. + +User space documentation can be found here: :doc:`/userspace-api/landlock`. + +Guiding principles for safe access controls +=========================================== + +* A Landlock rule shall be focused on access control on kernel objects instead + of syscall filtering (i.e. syscall arguments), which is the purpose of + seccomp-bpf. +* To avoid multiple kinds of side-channel attacks (e.g. leak of security + policies, CPU-based attacks), Landlock rules shall not be able to + programmatically communicate with user space. +* Kernel access check shall not slow down access request from unsandboxed + processes. +* Computation related to Landlock operations (e.g. enforcing a ruleset) shall + only impact the processes requesting them. + +Tests +===== + +Userspace tests for backward compatibility, ptrace restrictions and filesystem +support can be found here: `tools/testing/selftests/landlock/`_. + +Kernel structures +================= + +Object +------ + +.. kernel-doc:: security/landlock/object.h + :identifiers: + +Filesystem +---------- + +.. kernel-doc:: security/landlock/fs.h + :identifiers: + +Ruleset and domain +------------------ + +A domain is a read-only ruleset tied to a set of subjects (i.e. tasks' +credentials). Each time a ruleset is enforced on a task, the current domain is +duplicated and the ruleset is imported as a new layer of rules in the new +domain. Indeed, once in a domain, each rule is tied to a layer level. To +grant access to an object, at least one rule of each layer must allow the +requested action on the object. A task can then only transit to a new domain +that is the intersection of the constraints from the current domain and those +of a ruleset provided by the task. + +The definition of a subject is implicit for a task sandboxing itself, which +makes the reasoning much easier and helps avoid pitfalls. + +.. kernel-doc:: security/landlock/ruleset.h + :identifiers: + +.. Links +.. _tools/testing/selftests/landlock/: + https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/... diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index d29b020e5622..744c6491610c 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -18,6 +18,7 @@ place where this information is gathered.

no_new_privs seccomp_filter + landlock unshare spec_ctrl accelerators/ocxl diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst new file mode 100644 index 000000000000..b1040311402d --- /dev/null +++ b/Documentation/userspace-api/landlock.rst @@ -0,0 +1,311 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2017-2020 Mickaël Salaün mic@digikod.net +.. Copyright © 2019-2020 ANSSI +.. Copyright © 2021 Microsoft Corporation + +===================================== +Landlock: unprivileged access control +===================================== + +:Author: Mickaël Salaün +:Date: March 2021 + +The goal of Landlock is to enable to restrict ambient rights (e.g. global +filesystem access) for a set of processes. Because Landlock is a stackable +LSM, it makes possible to create safe security sandboxes as new security layers +in addition to the existing system-wide access-controls. This kind of sandbox +is expected to help mitigate the security impact of bugs or +unexpected/malicious behaviors in user space applications. Landlock empowers +any process, including unprivileged ones, to securely restrict themselves. + +Landlock rules +============== + +A Landlock rule describes an action on an object. An object is currently a +file hierarchy, and the related filesystem actions are defined with `access +rights`_. A set of rules is aggregated in a ruleset, which can then restrict +the thread enforcing it, and its future children. + +Defining and enforcing a security policy +---------------------------------------- + +We first need to create the ruleset that will contain our rules. For this +example, the ruleset will contain rules that only allow read actions, but write +actions will be denied. The ruleset then needs to handle both of these kind of +actions. + +.. code-block:: c + + int ruleset_fd; + struct landlock_ruleset_attr ruleset_attr = { + .handled_access_fs = + LANDLOCK_ACCESS_FS_EXECUTE | + LANDLOCK_ACCESS_FS_WRITE_FILE | + LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_READ_DIR | + LANDLOCK_ACCESS_FS_REMOVE_DIR | + LANDLOCK_ACCESS_FS_REMOVE_FILE | + LANDLOCK_ACCESS_FS_MAKE_CHAR | + LANDLOCK_ACCESS_FS_MAKE_DIR | + LANDLOCK_ACCESS_FS_MAKE_REG | + LANDLOCK_ACCESS_FS_MAKE_SOCK | + LANDLOCK_ACCESS_FS_MAKE_FIFO | + LANDLOCK_ACCESS_FS_MAKE_BLOCK | + LANDLOCK_ACCESS_FS_MAKE_SYM, + }; + + ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); + if (ruleset_fd < 0) { + perror("Failed to create a ruleset"); + return 1; + } + +We can now add a new rule to this ruleset thanks to the returned file +descriptor referring to this ruleset. The rule will only allow reading the +file hierarchy ``/usr``. Without another rule, write actions would then be +denied by the ruleset. To add ``/usr`` to the ruleset, we open it with the +``O_PATH`` flag and fill the &struct landlock_path_beneath_attr with this file +descriptor. + +.. code-block:: c + + int err; + struct landlock_path_beneath_attr path_beneath = { + .allowed_access = + LANDLOCK_ACCESS_FS_EXECUTE | + LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_READ_DIR, + }; + + path_beneath.parent_fd = open("/usr", O_PATH | O_CLOEXEC); + if (path_beneath.parent_fd < 0) { + perror("Failed to open file"); + close(ruleset_fd); + return 1; + } + err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH, + &path_beneath, 0); + close(path_beneath.parent_fd); + if (err) { + perror("Failed to update ruleset"); + close(ruleset_fd); + return 1; + } + +We now have a ruleset with one rule allowing read access to ``/usr`` while +denying all other handled accesses for the filesystem. The next step is to +restrict the current thread from gaining more privileges (e.g. thanks to a SUID +binary). + +.. code-block:: c + + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { + perror("Failed to restrict privileges"); + close(ruleset_fd); + return 1; + } + +The current thread is now ready to sandbox itself with the ruleset. + +.. code-block:: c + + if (landlock_restrict_self(ruleset_fd, 0)) { + perror("Failed to enforce ruleset"); + close(ruleset_fd); + return 1; + } + close(ruleset_fd); + +If the `landlock_restrict_self` system call succeeds, the current thread is now +restricted and this policy will be enforced on all its subsequently created +children as well. Once a thread is landlocked, there is no way to remove its +security policy; only adding more restrictions is allowed. These threads are +now in a new Landlock domain, merge of their parent one (if any) with the new +ruleset. + +Full working code can be found in `samples/landlock/sandboxer.c`_. + +Layers of file path access rights +--------------------------------- + +Each time a thread enforces a ruleset on itself, it updates its Landlock domain +with a new layer of policy. Indeed, this complementary policy is stacked with +the potentially other rulesets already restricting this thread. A sandboxed +thread can then safely add more constraints to itself with a new enforced +ruleset. + +One policy layer grants access to a file path if at least one of its rules +encountered on the path grants the access. A sandboxed thread can only access +a file path if all its enforced policy layers grant the access as well as all +the other system access controls (e.g. filesystem DAC, other LSM policies, +etc.). + +Bind mounts and OverlayFS +------------------------- + +Landlock enables to restrict access to file hierarchies, which means that these +access rights can be propagated with bind mounts (cf. +:doc:`/filesystems/sharedsubtree`) but not with :doc:`/filesystems/overlayfs`. + +A bind mount mirrors a source file hierarchy to a destination. The destination +hierarchy is then composed of the exact same files, on which Landlock rules can +be tied, either via the source or the destination path. These rules restrict +access when they are encountered on a path, which means that they can restrict +access to multiple file hierarchies at the same time, whether these hierarchies +are the result of bind mounts or not. + +An OverlayFS mount point consists of upper and lower layers. These layers are +combined in a merge directory, result of the mount point. This merge hierarchy +may include files from the upper and lower layers, but modifications performed +on the merge hierarchy only reflects on the upper layer. From a Landlock +policy point of view, each OverlayFS layers and merge hierarchies are +standalone and contains their own set of files and directories, which is +different from bind mounts. A policy restricting an OverlayFS layer will not +restrict the resulted merged hierarchy, and vice versa. Landlock users should +then only think about file hierarchies they want to allow access to, regardless +of the underlying filesystem. + +Inheritance +----------- + +Every new thread resulting from a :manpage:`clone(2)` inherits Landlock domain +restrictions from its parent. This is similar to the seccomp inheritance (cf. +:doc:`/userspace-api/seccomp_filter`) or any other LSM dealing with task's +:manpage:`credentials(7)`. For instance, one process's thread may apply +Landlock rules to itself, but they will not be automatically applied to other +sibling threads (unlike POSIX thread credential changes, cf. +:manpage:`nptl(7)`). + +When a thread sandboxes itself, we have the guarantee that the related security +policy will stay enforced on all this thread's descendants. This allows +creating standalone and modular security policies per application, which will +automatically be composed between themselves according to their runtime parent +policies. + +Ptrace restrictions +------------------- + +A sandboxed process has less privileges than a non-sandboxed process and must +then be subject to additional restrictions when manipulating another process. +To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target +process, a sandboxed process should have a subset of the target process rules, +which means the tracee must be in a sub-domain of the tracer. + +Kernel interface +================ + +Access rights +------------- + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: fs_access + +Creating a new ruleset +---------------------- + +.. kernel-doc:: security/landlock/syscalls.c + :identifiers: sys_landlock_create_ruleset + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: landlock_ruleset_attr + +Extending a ruleset +------------------- + +.. kernel-doc:: security/landlock/syscalls.c + :identifiers: sys_landlock_add_rule + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: landlock_rule_type landlock_path_beneath_attr + +Enforcing a ruleset +------------------- + +.. kernel-doc:: security/landlock/syscalls.c + :identifiers: sys_landlock_restrict_self + +Current limitations +=================== + +File renaming and linking +------------------------- + +Because Landlock targets unprivileged access controls, it is needed to properly +handle composition of rules. Such property also implies rules nesting. +Properly handling multiple layers of ruleset, each one of them able to restrict +access to files, also implies to inherit the ruleset restrictions from a parent +to its hierarchy. Because files are identified and restricted by their +hierarchy, moving or linking a file from one directory to another implies to +propagate the hierarchy constraints. To protect against privilege escalations +through renaming or linking, and for the sake of simplicity, Landlock currently +limits linking and renaming to the same directory. Future Landlock evolutions +will enable more flexibility for renaming and linking, with dedicated ruleset +flags. + +Filesystem layout modification +------------------------------ + +As for file renaming and linking, a sandboxed thread cannot modify its +filesystem layout, whether via :manpage:`mount(2)` or :manpage:`pivot_root(2)`. +However, :manpage:`chroot(2)` calls are not denied. + +Special filesystems +------------------- + +Access to regular files and directories can be restricted by Landlock, +according to the handled accesses of a ruleset. However, files that do not +come from a user-visible filesystem (e.g. pipe, socket), but can still be +accessed through ``/proc/<pid>/fd/*``, cannot currently be explicitly +restricted. Likewise, some special kernel filesystems such as nsfs, which can +be accessed through ``/proc/<pid>/ns/*``, cannot currently be explicitly +restricted. However, thanks to the `ptrace restrictions`_, access to such +sensitive ``/proc`` files are automatically restricted according to domain +hierarchies. Future Landlock evolutions could still enable to explicitly +restrict such paths with dedicated ruleset flags. + +Ruleset layers +-------------- + +There is a limit of 64 layers of stacked rulesets. This can be an issue for a +task willing to enforce a new ruleset in complement to its 64 inherited +rulesets. Once this limit is reached, sys_landlock_restrict_self() returns +E2BIG. It is then strongly suggested to carefully build rulesets once in the +life of a thread, especially for applications able to launch other applications +that may also want to sandbox themselves (e.g. shells, container managers, +etc.). + +Memory usage +------------ + +Kernel memory allocated to create rulesets is accounted and can be restricted +by the :doc:`/admin-guide/cgroup-v1/memory`. + +Questions and answers +===================== + +What about user space sandbox managers? +--------------------------------------- + +Using user space process to enforce restrictions on kernel resources can lead +to race conditions or inconsistent evaluations (i.e. `Incorrect mirroring of +the OS code and state +https://www.ndss-symposium.org/ndss2003/traps-and-pitfalls-practical-problems-system-call-interposition-based-security-tools/`_). + +What about namespaces and containers? +------------------------------------- + +Namespaces can help create sandboxes but they are not designed for +access-control and then miss useful features for such use case (e.g. no +fine-grained restrictions). Moreover, their complexity can lead to security +issues, especially when untrusted processes can manipulate them (cf. +`Controlling access to user namespaces https://lwn.net/Articles/673597/`_). + +Additional documentation +======================== + +* :doc:`/security/landlock` +* https://landlock.io + +.. Links +.. _samples/landlock/sandboxer.c: + https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/sample... diff --git a/MAINTAINERS b/MAINTAINERS index 88175ed1f315..7b0c6de5946a 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -10003,6 +10003,8 @@ L: linux-security-module@vger.kernel.org S: Supported W: https://landlock.io T: git https://github.com/landlock-lsm/linux.git +F: Documentation/security/landlock.rst +F: Documentation/userspace-api/landlock.rst F: include/uapi/linux/landlock.h F: samples/landlock/ F: security/landlock/