// SPDX-License-Identifier: GPL-2.0-only
/*
* Landlock - Filesystem management and hooks
*
* Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
* Copyright © 2018-2020 ANSSI
* Copyright © 2021-2025 Microsoft Corporation
* Copyright © 2022 Günther Noack <gnoack3000@gmail.com>
* Copyright © 2023-2024 Google LLC
*/
#include <asm/ioctls.h>
#include <kunit/test.h>
#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/falloc.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kdev_t.h>
#include <linux/kernel.h>
#include <linux/limits.h>
#include <linux/list.h>
#include <linux/lsm_audit.h>
#include <linux/lsm_hooks.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/net.h>
#include <linux/path.h>
#include <linux/pid.h>
#include <linux/rcupdate.h>
#include <linux/sched/signal.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/types.h>
#include <linux/wait_bit.h>
#include <linux/workqueue.h>
#include <net/af_unix.h>
#include <uapi/linux/fiemap.h>
#include <uapi/linux/landlock.h>
#include "access.h"
#include "audit.h"
#include "common.h"
#include "cred.h"
#include "domain.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
};
/* IOCTL helpers */
/**
* is_masked_device_ioctl - Determine whether an IOCTL command is always
* permitted with Landlock for device files. These commands can not be
* restricted on device files by enforcing a Landlock policy.
*
* @cmd: The IOCTL command that is supposed to be run.
*
* By default, any IOCTL on a device file requires the
* LANDLOCK_ACCESS_FS_IOCTL_DEV right. However, we blanket-permit some
* commands, if:
*
* 1. The command is implemented in fs/ioctl.c's do_vfs_ioctl(),
* not in f_ops->unlocked_ioctl() or f_ops->compat_ioctl().
*
* 2. The command is harmless when invoked on devices.
*
* We also permit commands that do not make sense for devices, but where the
* do_vfs_ioctl() implementation returns a more conventional error code.
*
* Any new IOCTL commands that are implemented in fs/ioctl.c's do_vfs_ioctl()
* should be considered for inclusion here.
*
* Return: True if the IOCTL @cmd can not be restricted with Landlock for
* device files, false otherwise.
*/
static __attribute_const__ bool is_masked_device_ioctl(const unsigned int cmd)
{
switch (cmd) {
/*
* FIOCLEX, FIONCLEX, FIONBIO and FIOASYNC manipulate the FD's
* close-on-exec and the file's buffered-IO and async flags. These
* operations are also available through fcntl(2), and are
* unconditionally permitted in Landlock.
*/
case FIOCLEX:
case FIONCLEX:
case FIONBIO:
case FIOASYNC:
/*
* FIOQSIZE queries the size of a regular file, directory, or link.
*
* We still permit it, because it always returns -ENOTTY for
* other file types.
*/
case FIOQSIZE:
/*
* FIFREEZE and FITHAW freeze and thaw the file system which the
* given file belongs to. Requires CAP_SYS_ADMIN.
*
* These commands operate on the file system's superblock rather
* than on the file itself. The same operations can also be
* done through any other file or directory on the same file
* system, so it is safe to permit these.
*/
case FIFREEZE:
case FITHAW:
/*
* FS_IOC_FIEMAP queries information about the allocation of
* blocks within a file.
*
* This IOCTL command only makes sense for regular files and is
* not implemented by devices. It is harmless to permit.
*/
case FS_IOC_FIEMAP:
/*
* FIGETBSZ queries the file system's block size for a file or
* directory.
*
* This command operates on the file system's superblock rather
* than on the file itself. The same operation can also be done
* through any other file or directory on the same file system,
* so it is safe to permit it.
*/
case FIGETBSZ:
/*
* FICLONE, FICLONERANGE and FIDEDUPERANGE make files share
* their underlying storage ("reflink") between source and
* destination FDs, on file systems which support that.
*
* These IOCTL commands only apply to regular files
* and are harmless to permit for device files.
*/
case FICLONE:
case FICLONERANGE:
case FIDEDUPERANGE:
/*
* FS_IOC_GETFSUUID and FS_IOC_GETFSSYSFSPATH both operate on
* the file system superblock, not on the specific file, so
* these operations are available through any other file on the
* same file system as well.
*/
case FS_IOC_GETFSUUID:
case FS_IOC_GETFSSYSFSPATH:
return true;
/*
* FIONREAD, FS_IOC_GETFLAGS, FS_IOC_SETFLAGS, FS_IOC_FSGETXATTR and
* FS_IOC_FSSETXATTR are forwarded to device implementations.
*/
/*
* file_ioctl() commands (FIBMAP, FS_IOC_RESVSP, FS_IOC_RESVSP64,
* FS_IOC_UNRESVSP, FS_IOC_UNRESVSP64 and FS_IOC_ZERO_RANGE) are
* forwarded to device implementations, so not permitted.
*/
/* Other commands are guarded by the access right. */
default:
return false;
}
}
/*
* is_masked_device_ioctl_compat - same as the helper above, but checking the
* "compat" IOCTL commands.
*
* The IOCTL commands with special handling in compat-mode should behave the
* same as their non-compat counterparts.
*/
static __attribute_const__ bool
is_masked_device_ioctl_compat(const unsigned int cmd)
{
switch (cmd) {
/* FICLONE is permitted, same as in the non-compat variant. */
case FICLONE:
return true;
#if defined(CONFIG_X86_64)
/*
* FS_IOC_RESVSP_32, FS_IOC_RESVSP64_32, FS_IOC_UNRESVSP_32,
* FS_IOC_UNRESVSP64_32, FS_IOC_ZERO_RANGE_32: not blanket-permitted,
* for consistency with their non-compat variants.
*/
case FS_IOC_RESVSP_32:
case FS_IOC_RESVSP64_32:
case FS_IOC_UNRESVSP_32:
case FS_IOC_UNRESVSP64_32:
case FS_IOC_ZERO_RANGE_32:
#endif
/*
* FS_IOC32_GETFLAGS, FS_IOC32_SETFLAGS are forwarded to their device
* implementations.
*/
case FS_IOC32_GETFLAGS:
case FS_IOC32_SETFLAGS:
return false;
default:
return is_masked_device_ioctl(cmd);
}
}
/* 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. */
/* clang-format off */
#define ACCESS_FILE ( \
LANDLOCK_ACCESS_FS_EXECUTE | \
LANDLOCK_ACCESS_FS_WRITE_FILE | \
LANDLOCK_ACCESS_FS_READ_FILE | \
LANDLOCK_ACCESS_FS_TRUNCATE | \
LANDLOCK_ACCESS_FS_IOCTL_DEV | \
LANDLOCK_ACCESS_FS_RESOLVE_UNIX)
/* clang-format on */
/*
* @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,
access_mask_t access_rights, const u32 flags)
{
int err;
struct landlock_id id = {
.type = LANDLOCK_KEY_INODE,
};
/* Files only get access rights that make sense. */
if (!d_is_dir(path->dentry) &&
!access_mask_subset(access_rights, 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 &
~landlock_get_fs_access_mask(ruleset, 0);
id.key.object = get_inode_object(d_backing_inode(path->dentry));
if (IS_ERR(id.key.object))
return PTR_ERR(id.key.object);
mutex_lock(&ruleset->lock);
err = landlock_insert_rule(ruleset, id, access_rights, flags);
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(id.key.object);
return err;
}
/* Access-control management */
/*
* The lifetime of the returned rule is tied to @domain.
*
* Returns NULL if no rule is found or if @dentry is negative.
*/
static const struct landlock_rule *
find_rule(const struct landlock_ruleset *const domain,
const struct dentry *const dentry)
{
const struct landlock_rule *rule;
const struct inode *inode;
struct landlock_id id = {
.type = LANDLOCK_KEY_INODE,
};
/* Ignores nonexistent leafs. */
if (d_is_negative(dentry))
return NULL;
inode = d_backing_inode(dentry);
rcu_read_lock();
id.key.object = rcu_dereference(landlock_inode(inode)->object);
rule = landlock_find_rule(domain, id);
rcu_read_unlock();
return rule;
}
/*
* 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>
*/
static bool is_nouser_or_private(const struct dentry *dentry)
{
return (dentry->d_sb->s_flags & SB_NOUSER) ||
(d_is_positive(dentry) &&
unlikely(IS_PRIVATE(d_backing_inode(dentry))));
}
static const struct access_masks any_fs = {
.fs = ~0,
};
/*
* Returns true iff the child file with the given src_child access rights under
* src_parent would result in having the same or fewer access rights if it were
* moved under new_parent.
*/
static bool may_refer(const struct layer_masks *const src_parent,
const struct layer_masks *const src_child,
const struct layer_masks *const new_parent,
const bool child_is_dir)
{
for (size_t i = 0; i < ARRAY_SIZE(new_parent->layers); i++) {
access_mask_t child_access = src_parent->layers[i].access &
src_child->layers[i].access;
access_mask_t parent_access = new_parent->layers[i].access;
if (!child_is_dir) {
child_access &= ACCESS_FILE;
parent_access &= ACCESS_FILE;
}
if (!access_mask_subset(child_access, parent_access))
return false;
}
return true;
}
/*
* Check that a destination file hierarchy has more restrictions than a source
* file hierarchy. This is only used for link and rename actions.
*
* Return: True if child1 may be moved from parent1 to parent2 without
* increasing its access rights (if child2 is set, an additional condition is
* that child2 may be used from parent2 to parent1 without increasing its access
* rights), false otherwise.
*/
static bool no_more_access(const struct layer_masks *const parent1,
const struct layer_masks *const child1,
const bool child1_is_dir,
const struct layer_masks *const parent2,
const struct layer_masks *const child2,
const bool child2_is_dir)
{
if (!may_refer(parent1, child1, parent2, child1_is_dir))
return false;
if (!child2)
return true;
return may_refer(parent2, child2, parent1, child2_is_dir);
}
#define NMA_TRUE(...) KUNIT_EXPECT_TRUE(test, no_more_access(__VA_ARGS__))
#define NMA_FALSE(...) KUNIT_EXPECT_FALSE(test, no_more_access(__VA_ARGS__))
#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
static void test_no_more_access(struct kunit *const test)
{
const struct layer_masks rx0 = {
.layers[0].access = LANDLOCK_ACCESS_FS_EXECUTE |
LANDLOCK_ACCESS_FS_READ_FILE,
};
const struct layer_masks mx0 = {
.layers[0].access = LANDLOCK_ACCESS_FS_EXECUTE |
LANDLOCK_ACCESS_FS_MAKE_REG,
};
const struct layer_masks x0 = {
.layers[0].access = LANDLOCK_ACCESS_FS_EXECUTE,
};
const struct layer_masks x1 = {
.layers[1].access = LANDLOCK_ACCESS_FS_EXECUTE,
};
const struct layer_masks x01 = {
.layers[0].access = LANDLOCK_ACCESS_FS_EXECUTE,
.layers[1].access = LANDLOCK_ACCESS_FS_EXECUTE,
};
const struct layer_masks allows_all = {};
/* Checks without restriction. */
NMA_TRUE(&x0, &allows_all, false, &allows_all, NULL, false);
NMA_TRUE(&allows_all, &x0, false, &allows_all, NULL, false);
NMA_FALSE(&x0, &x0, false, &allows_all, NULL, false);
/*
* Checks that we can only refer a file if no more access could be
* inherited.
*/
NMA_TRUE(&x0, &x0, false, &rx0, NULL, false);
NMA_TRUE(&rx0, &rx0, false, &rx0, NULL, false);
NMA_FALSE(&rx0, &rx0, false, &x0, NULL, false);
NMA_FALSE(&rx0, &rx0, false, &x1, NULL, false);
/* Checks allowed referring with different nested domains. */
NMA_TRUE(&x0, &x1, false, &x0, NULL, false);
NMA_TRUE(&x1, &x0, false, &x0, NULL, false);
NMA_TRUE(&x0, &x01, false, &x0, NULL, false);
NMA_TRUE(&x0, &x01, false, &rx0, NULL, false);
NMA_TRUE(&x01, &x0, false, &x0, NULL, false);
NMA_TRUE(&x01, &x0, false, &rx0, NULL, false);
NMA_FALSE(&x01, &x01, false, &x0, NULL, false);
/* Checks that file access rights are also enforced for a directory. */
NMA_FALSE(&rx0, &rx0, true, &x0, NULL, false);
/* Checks that directory access rights don't impact file referring... */
NMA_TRUE(&mx0, &mx0, false, &x0, NULL, false);
/* ...but only directory referring. */
NMA_FALSE(&mx0, &mx0, true, &x0, NULL, false);
/* Checks directory exchange. */
NMA_TRUE(&mx0, &mx0, true, &mx0, &mx0, true);
NMA_TRUE(&mx0, &mx0, true, &mx0, &x0, true);
NMA_FALSE(&mx0, &mx0, true, &x0, &mx0, true);
NMA_FALSE(&mx0, &mx0, true, &x0, &x0, true);
NMA_FALSE(&mx0, &mx0, true, &x1, &x1, true);
/* Checks file exchange with directory access rights... */
NMA_TRUE(&mx0, &mx0, false, &mx0, &mx0, false);
NMA_TRUE(&mx0, &mx0, false, &mx0, &x0, false);
NMA_TRUE(&mx0, &mx0, false, &x0, &mx0, false);
NMA_TRUE(&mx0, &mx0, false, &x0, &x0, false);
/* ...and with file access rights. */
NMA_TRUE(&rx0, &rx0, false, &rx0, &rx0, false);
NMA_TRUE(&rx0, &rx0, false, &rx0, &x0, false);
NMA_FALSE(&rx0, &rx0, false, &x0, &rx0, false);
NMA_FALSE(&rx0, &rx0, false, &x0, &x0, false);
NMA_FALSE(&rx0, &rx0, false, &x1, &x1, false);
/*
* Allowing the following requests should not be a security risk
* because domain 0 denies execute access, and domain 1 is always
* nested with domain 0. However, adding an exception for this case
* would mean to check all nested domains to make sure none can get
* more privileges (e.g. processes only sandboxed by domain 0).
* Moreover, this behavior (i.e. composition of N domains) could then
* be inconsistent compared to domain 1's ruleset alone (e.g. it might
* be denied to link/rename with domain 1's ruleset, whereas it would
* be allowed if nested on top of domain 0). Another drawback would be
* to create a cover channel that could enable sandboxed processes to
* infer most of the filesystem restrictions from their domain. To
* make it simple, efficient, safe, and more consistent, this case is
* always denied.
*/
NMA_FALSE(&x1, &x1, false, &x0, NULL, false);
NMA_FALSE(&x1, &x1, false, &rx0, NULL, false);
NMA_FALSE(&x1, &x1, true, &x0, NULL, false);
NMA_FALSE(&x1, &x1, true, &rx0, NULL, false);
/* Checks the same case of exclusive domains with a file... */
NMA_TRUE(&x1, &x1, false, &x01, NULL, false);
NMA_FALSE(&x1, &x1, false, &x01, &x0, false);
NMA_FALSE(&x1, &x1, false, &x01, &x01, false);
NMA_FALSE(&x1, &x1, false, &x0, &x0, false);
/* ...and with a directory. */
NMA_FALSE(&x1, &x1, false, &x0, &x0, true);
NMA_FALSE(&x1, &x1, true, &x0, &x0, false);
NMA_FALSE(&x1, &x1, true, &x0, &x0, true);
}
#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
#undef NMA_TRUE
#undef NMA_FALSE
static bool is_layer_masks_allowed(const struct layer_masks *masks)
{
for (size_t i = 0; i < ARRAY_SIZE(masks->layers); i++) {
if (masks->layers[i].access)
return false;
}
return true;
}
/*
* Removes @masks accesses that are not requested.
*
* Returns true if the request is allowed, false otherwise.
*/
static bool scope_to_request(const access_mask_t access_request,
struct layer_masks *masks)
{
bool saw_unfulfilled_access = false;
if (WARN_ON_ONCE(!masks))
return true;
for (size_t i = 0; i < ARRAY_SIZE(masks->layers); i++) {
masks->layers[i].access &= access_request;
if (masks->layers[i].access)
saw_unfulfilled_access = true;
}
return !saw_unfulfilled_access;
}
#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
static void test_scope_to_request_with_exec_none(struct kunit *const test)
{
/* Allows everything. */
struct layer_masks masks = {};
/* Checks and scopes with execute. */
KUNIT_EXPECT_TRUE(test,
scope_to_request(LANDLOCK_ACCESS_FS_EXECUTE, &masks));
KUNIT_EXPECT_EQ(test, 0, (access_mask_t)masks.layers[0].access);
}
static void test_scope_to_request_with_exec_some(struct kunit *const test)
{
/* Denies execute and write. */
struct layer_masks masks = {
.layers[0].access = LANDLOCK_ACCESS_FS_EXECUTE,
.layers[1].access = LANDLOCK_ACCESS_FS_WRITE_FILE,
};
/* Checks and scopes with execute. */
KUNIT_EXPECT_FALSE(test, scope_to_request(LANDLOCK_ACCESS_FS_EXECUTE,
&masks));
/*
* These casts to access_mask_t are needed because typeof(), used in
* KUNIT_EXPECT_EQ(), does not work on bitfields.
*/
KUNIT_EXPECT_EQ(test, LANDLOCK_ACCESS_FS_EXECUTE,
(access_mask_t)masks.layers[0].access);
KUNIT_EXPECT_EQ(test, 0, (access_mask_t)masks.layers[1].access);
}
static void test_scope_to_request_without_access(struct kunit *const test)
{
/* Denies execute and write. */
struct layer_masks masks = {
.layers[0].access = LANDLOCK_ACCESS_FS_EXECUTE,
.layers[1].access = LANDLOCK_ACCESS_FS_WRITE_FILE,
};
/* Checks and scopes without access request. */
KUNIT_EXPECT_TRUE(test, scope_to_request(0, &masks));
KUNIT_EXPECT_EQ(test, 0, (access_mask_t)masks.layers[0].access);
KUNIT_EXPECT_EQ(test, 0, (access_mask_t)masks.layers[1].access);
}
#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
/*
* Returns true if there is at least one access right different than
* LANDLOCK_ACCESS_FS_REFER.
*/
static bool is_eacces(const struct layer_masks *masks,
const access_mask_t access_request)
{
if (!masks)
return false;
for (size_t i = 0; i < ARRAY_SIZE(masks->layers); i++) {
/* LANDLOCK_ACCESS_FS_REFER alone must return -EXDEV. */
if (masks->layers[i].access & access_request &
~LANDLOCK_ACCESS_FS_REFER)
return true;
}
return false;
}
#define IE_TRUE(...) KUNIT_EXPECT_TRUE(test, is_eacces(__VA_ARGS__))
#define IE_FALSE(...) KUNIT_EXPECT_FALSE(test, is_eacces(__VA_ARGS__))
#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
static void test_is_eacces_with_none(struct kunit *const test)
{
const struct layer_masks masks = {};
IE_FALSE(&masks, 0);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_REFER);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_EXECUTE);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_WRITE_FILE);
}
static void test_is_eacces_with_refer(struct kunit *const test)
{
const struct layer_masks masks = {
.layers[0].access = LANDLOCK_ACCESS_FS_REFER,
};
IE_FALSE(&masks, 0);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_REFER);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_EXECUTE);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_WRITE_FILE);
}
static void test_is_eacces_with_write(struct kunit *const test)
{
const struct layer_masks masks = {
.layers[0].access = LANDLOCK_ACCESS_FS_WRITE_FILE,
};
IE_FALSE(&masks, 0);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_REFER);
IE_FALSE(&masks, LANDLOCK_ACCESS_FS_EXECUTE);
IE_TRUE(&masks, LANDLOCK_ACCESS_FS_WRITE_FILE);
}
#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
#undef IE_TRUE
#undef IE_FALSE
/**
* is_access_to_paths_allowed - Check accesses for requests with a common path
*
* @domain: Domain to check against.
* @path: File hierarchy to walk through. For refer checks, this would be
* the common mountpoint.
* @access_request_parent1: Accesses to check, once @layer_masks_parent1 is
* equal to @layer_masks_parent2 (if any). This is tied to the unique
* requested path for most actions, or the source in case of a refer action
* (i.e. rename or link), or the source and destination in case of
* RENAME_EXCHANGE.
* @layer_masks_parent1: Pointer to a matrix of layer masks per access
* masks, identifying the layers that forbid a specific access. Bits from
* this matrix can be unset according to the @path walk. An empty matrix
* means that @domain allows all possible Landlock accesses (i.e. not only
* those identified by @access_request_parent1). This matrix can
* initially refer to domain layer masks and, when the accesses for the
* destination and source are the same, to requested layer masks.
* @log_request_parent1: Audit request to fill if the related access is denied.
* @dentry_child1: Dentry to the initial child of the parent1 path. This
* pointer must be NULL for non-refer actions (i.e. not link nor rename).
* @access_request_parent2: Similar to @access_request_parent1 but for a
* request involving a source and a destination. This refers to the
* destination, except in case of RENAME_EXCHANGE where it also refers to
* the source. Must be set to 0 when using a simple path request.
* @layer_masks_parent2: Similar to @layer_masks_parent1 but for a refer
* action. This must be NULL otherwise.
* @log_request_parent2: Audit request to fill if the related access is denied.
* @dentry_child2: Dentry to the initial child of the parent2 path. This
* pointer is only set for RENAME_EXCHANGE actions and must be NULL
* otherwise.
*
* This helper first checks that the destination has a superset of restrictions
* compared to the source (if any) for a common path. Because of
* RENAME_EXCHANGE actions, source and destinations may be swapped. It then
* checks that the collected accesses and the remaining ones are enough to
* allow the request.
*
* Return: True if the access request is granted, false otherwise.
*/
static bool
is_access_to_paths_allowed(const struct landlock_ruleset *const domain,
const struct path *const path,
const access_mask_t access_request_parent1,
struct layer_masks *layer_masks_parent1,
struct landlock_request *const log_request_parent1,
struct dentry *const dentry_child1,
const access_mask_t access_request_parent2,
struct layer_masks *layer_masks_parent2,
struct landlock_request *const log_request_parent2,
struct dentry *const dentry_child2)
{
bool allowed_parent1 = false, allowed_parent2 = false, is_dom_check,
child1_is_directory = true, child2_is_directory = true;
struct path walker_path;
access_mask_t access_masked_parent1, access_masked_parent2;
struct layer_masks _layer_masks_child1, _layer_masks_child2;
struct layer_masks *layer_masks_child1 = NULL,
*layer_masks_child2 = NULL;
if (!access_request_parent1 && !access_request_parent2)
return true;
if (WARN_ON_ONCE(!path))
return true;
if (is_nouser_or_private(path->dentry))
return true;
if (WARN_ON_ONCE(!layer_masks_parent1))
return false;
allowed_parent1 = is_layer_masks_allowed(layer_masks_parent1);
if (unlikely(layer_masks_parent2)) {
if (WARN_ON_ONCE(!dentry_child1))
return false;
allowed_parent2 = is_layer_masks_allowed(layer_masks_parent2);
/*
* For a double request, first check for potential privilege
* escalation by looking at domain handled accesses (which are
* a superset of the meaningful requested accesses).
*/
access_masked_parent1 = access_masked_parent2 =
landlock_union_access_masks(domain).fs;
is_dom_check = true;
} else {
if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
return false;
/* For a simple request, only check for requested accesses. */
access_masked_parent1 = access_request_parent1;
access_masked_parent2 = access_request_parent2;
is_dom_check = false;
}
if (unlikely(dentry_child1)) {
/*
* Get the layer masks for the child dentries for use by domain
* check later.
*/
if (landlock_init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
&_layer_masks_child1,
LANDLOCK_KEY_INODE))
landlock_unmask_layers(find_rule(domain, dentry_child1),
&_layer_masks_child1);
layer_masks_child1 = &_layer_masks_child1;
child1_is_directory = d_is_dir(dentry_child1);
}
if (unlikely(dentry_child2)) {
if (landlock_init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
&_layer_masks_child2,
LANDLOCK_KEY_INODE))
landlock_unmask_layers(find_rule(domain, dentry_child2),
&_layer_masks_child2);
layer_masks_child2 = &_layer_masks_child2;
child2_is_directory = d_is_dir(dentry_child2);
}
walker_path = *path;
path_get(&walker_path);
/*
* We need to walk through all the hierarchy to not miss any relevant
* restriction.
*/
while (true) {
const struct landlock_rule *rule;
/*
* If at least all accesses allowed on the destination are
* already allowed on the source, respectively if there is at
* least as much as restrictions on the destination than on the
* source, then we can safely refer files from the source to
* the destination without risking a privilege escalation.
* This also applies in the case of RENAME_EXCHANGE, which
* implies checks on both direction. This is crucial for
* standalone multilayered security policies. Furthermore,
* this helps avoid policy writers to shoot themselves in the
* foot.
*/
if (unlikely(is_dom_check &&
no_more_access(
layer_masks_parent1, layer_masks_child1,
child1_is_directory, layer_masks_parent2,
layer_masks_child2,
child2_is_directory))) {
/*
* Now, downgrades the remaining checks from domain
* handled accesses to requested accesses.
*/
is_dom_check = false;
access_masked_parent1 = access_request_parent1;
access_masked_parent2 = access_request_parent2;
allowed_parent1 =
allowed_parent1 ||
scope_to_request(access_masked_parent1,
layer_masks_parent1);
allowed_parent2 =
allowed_parent2 ||
scope_to_request(access_masked_parent2,
layer_masks_parent2);
/* Stops when all accesses are granted. */
if (allowed_parent1 && allowed_parent2)
break;
}
rule = find_rule(domain, walker_path.dentry);
allowed_parent1 =
allowed_parent1 ||
landlock_unmask_layers(rule, layer_masks_parent1);
allowed_parent2 =
allowed_parent2 ||
landlock_unmask_layers(rule, layer_masks_parent2);
/* Stops when a rule from each layer grants access. */
if (allowed_parent1 && allowed_parent2)
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.
*/
break;
}
}
if (unlikely(IS_ROOT(walker_path.dentry))) {
if (likely(walker_path.mnt->mnt_flags & MNT_INTERNAL)) {
/*
* Stops and allows access when reaching disconnected root
* directories that are part of internal filesystems (e.g. nsfs,
* which is reachable through /proc/<pid>/ns/<namespace>).
*/
allowed_parent1 = true;
allowed_parent2 = true;
break;
}
/*
* We reached a disconnected root directory from a bind mount.
* Let's continue the walk with the mount point we missed.
*/
dput(walker_path.dentry);
walker_path.dentry = walker_path.mnt->mnt_root;
dget(walker_path.dentry);
} else {
struct dentry *const parent_dentry =
dget_parent(walker_path.dentry);
dput(walker_path.dentry);
walker_path.dentry = parent_dentry;
}
}
path_put(&walker_path);
/*
* Check CONFIG_AUDIT to enable elision of log_request_parent* and
* associated caller's stack variables thanks to dead code elimination.
*/
#ifdef CONFIG_AUDIT
if (!allowed_parent1 && log_request_parent1) {
log_request_parent1->type = LANDLOCK_REQUEST_FS_ACCESS;
log_request_parent1->audit.type = LSM_AUDIT_DATA_PATH;
log_request_parent1->audit.u.path = *path;
log_request_parent1->access = access_masked_parent1;
log_request_parent1->layer_masks = layer_masks_parent1;
}
if (!allowed_parent2 && log_request_parent2) {
log_request_parent2->type = LANDLOCK_REQUEST_FS_ACCESS;
log_request_parent2->audit.type = LSM_AUDIT_DATA_PATH;
log_request_parent2->audit.u.path = *path;
log_request_parent2->access = access_masked_parent2;
log_request_parent2->layer_masks = layer_masks_parent2;
}
#endif /* CONFIG_AUDIT */
return allowed_parent1 && allowed_parent2;
}
static int current_check_access_path(const struct path *const path,
access_mask_t access_request)
{
const struct access_masks masks = {
.fs = access_request,
};
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), masks, NULL);
struct layer_masks layer_masks;
struct landlock_request request = {};
if (!subject)
return 0;
access_request = landlock_init_layer_masks(subject->domain,
access_request, &layer_masks,
LANDLOCK_KEY_INODE);
if (is_access_to_paths_allowed(subject->domain, path, access_request,
&layer_masks, &request, NULL, 0, NULL,
NULL, NULL))
return 0;
landlock_log_denial(subject, &request);
return -EACCES;
}
static __attribute_const__ access_mask_t get_mode_access(const umode_t mode,
const dev_t dev)
{
switch (mode & S_IFMT) {
case S_IFLNK:
return LANDLOCK_ACCESS_FS_MAKE_SYM;
case S_IFDIR:
return LANDLOCK_ACCESS_FS_MAKE_DIR;
case S_IFCHR:
/* Whiteout objects are guarded with MAKE_REG. */
if (dev == WHITEOUT_DEV)
return LANDLOCK_ACCESS_FS_MAKE_REG;
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;
case S_IFREG:
case 0:
/* A zero mode translates to S_IFREG. */
default:
/* Treats weird files as regular files. */
return LANDLOCK_ACCESS_FS_MAKE_REG;
}
}
static access_mask_t get_dentry_access(const struct dentry *const dentry)
{
const struct inode *const inode = d_backing_inode(dentry);
return get_mode_access(inode->i_mode, inode->i_rdev);
}
static access_mask_t 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;
}
/**
* collect_domain_accesses - Walk through a file path and collect accesses
*
* @domain: Domain to check against.
* @mnt_root: Last directory to check.
* @dir: Directory to start the walk from.
* @layer_masks_dom: Where to store the collected accesses.
*
* This helper is useful to begin a path walk from the @dir directory to a
* @mnt_root directory used as a mount point. This mount point is the common
* ancestor between the source and the destination of a renamed and linked
* file. While walking from @dir to @mnt_root, we record all the domain's
* allowed accesses in @layer_masks_dom.
*
* Because of disconnected directories, this walk may not reach @mnt_dir. In
* this case, the walk will continue to @mnt_dir after this call.
*
* This is similar to is_access_to_paths_allowed() but much simpler because it
* only handles walking on the same mount point and only checks one set of
* accesses.
*
* Return: True if all the domain access rights are allowed for @dir, false if
* the walk reached @mnt_root.
*/
static bool collect_domain_accesses(const struct landlock_ruleset *const domain,
const struct dentry *const mnt_root,
struct dentry *dir,
struct layer_masks *layer_masks_dom)
{
bool ret = false;
if (WARN_ON_ONCE(!domain || !mnt_root || !dir || !layer_masks_dom))
return true;
if (is_nouser_or_private(dir))
return true;
if (!landlock_init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
layer_masks_dom, LANDLOCK_KEY_INODE))
return true;
dget(dir);
while (true) {
struct dentry *parent_dentry;
/* Gets all layers allowing all domain accesses. */
if (landlock_unmask_layers(find_rule(domain, dir),
layer_masks_dom)) {
/*
* Stops when all handled accesses are allowed by at
* least one rule in each layer.
*/
ret = true;
break;
}
/*
* Stops at the mount point or the filesystem root for a disconnected
* directory.
*/
if (dir == mnt_root || unlikely(IS_ROOT(dir)))
break;
parent_dentry = dget_parent(dir);
dput(dir);
dir = parent_dentry;
}
dput(dir);
return ret;
}
/**
* current_check_refer_path - Check if a rename or link action is allowed
*
* @old_dentry: File or directory requested to be moved or linked.
* @new_dir: Destination parent directory.
* @new_dentry: Destination file or directory.
* @removable: Sets to true if it is a rename operation.
* @exchange: Sets to true if it is a rename operation with RENAME_EXCHANGE.
* @whiteout: Sets to true if it is a rename operation with RENAME_WHITEOUT.
*
* Because of its unprivileged constraints, Landlock relies on file hierarchies
* (and not only inodes) to tie access rights to files. Being able to link or
* rename a file hierarchy brings some challenges. Indeed, moving or linking a
* file (i.e. creating a new reference to an inode) can have an impact on the
* actions allowed for a set of files if it would change its parent directory
* (i.e. reparenting).
*
* To avoid trivial access right bypasses, Landlock first checks if the file or
* directory requested to be moved would gain new access rights inherited from
* its new hierarchy. Before returning any error, Landlock then checks that
* the parent source hierarchy and the destination hierarchy would allow the
* link or rename action. If it is not the case, an error with EACCES is
* returned to inform user space that there is no way to remove or create the
* requested source file type. If it should be allowed but the new inherited
* access rights would be greater than the source access rights, then the
* kernel returns an error with EXDEV. Prioritizing EACCES over EXDEV enables
* user space to abort the whole operation if there is no way to do it, or to
* manually copy the source to the destination if this remains allowed, e.g.
* because file creation is allowed on the destination directory but not direct
* linking.
*
* To achieve this goal, the kernel needs to compare two file hierarchies: the
* one identifying the source file or directory (including itself), and the
* destination one. This can be seen as a multilayer partial ordering problem.
* The kernel walks through these paths and collects in a matrix the access
* rights that are denied per layer. These matrices are then compared to see
* if the destination one has more (or the same) restrictions as the source
* one. If this is the case, the requested action will not return EXDEV, which
* doesn't mean the action is allowed. The parent hierarchy of the source
* (i.e. parent directory), and the destination hierarchy must also be checked
* to verify that they explicitly allow such action (i.e. referencing,
* creation and potentially removal rights). The kernel implementation is then
* required to rely on potentially four matrices of access rights: one for the
* source file or directory (i.e. the child), a potentially other one for the
* other source/destination (in case of RENAME_EXCHANGE), one for the source
* parent hierarchy and a last one for the destination hierarchy. These
* ephemeral matrices take some space on the stack, which limits the number of
* layers to a deemed reasonable number: 16.
*
* Return: 0 if access is allowed, -EXDEV if @old_dentry would inherit new
* access rights from @new_dir, or -EACCES if file removal or creation is
* denied.
*/
static int current_check_refer_path(struct dentry *const old_dentry,
const struct path *const new_dir,
struct dentry *const new_dentry,
const bool removable, const bool exchange,
const bool whiteout)
{
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), any_fs, NULL);
bool allow_parent1, allow_parent2;
access_mask_t access_request_parent1, access_request_parent2;
struct path mnt_dir;
struct dentry *old_parent;
struct layer_masks layer_masks_parent1 = {}, layer_masks_parent2 = {};
struct landlock_request request1 = {}, request2 = {};
if (!subject)
return 0;
if (unlikely(d_is_negative(old_dentry)))
return -ENOENT;
if (exchange) {
if (unlikely(d_is_negative(new_dentry)))
return -ENOENT;
access_request_parent1 = get_dentry_access(new_dentry);
} else {
access_request_parent1 = 0;
}
access_request_parent2 = get_dentry_access(old_dentry);
if (removable) {
access_request_parent1 |= maybe_remove(old_dentry);
access_request_parent2 |= maybe_remove(new_dentry);
}
/*
* In case of renameat2(2) with RENAME_WHITEOUT, a whiteout object is
* created in the source location, so we require an additional access
* right there.
*/
if (whiteout)
access_request_parent1 |=
get_mode_access(S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
/* The mount points are the same for old and new paths, cf. EXDEV. */
if (old_dentry->d_parent == new_dir->dentry) {
/*
* The LANDLOCK_ACCESS_FS_REFER access right is not required
* for same-directory referer (i.e. no reparenting).
*/
access_request_parent1 = landlock_init_layer_masks(
subject->domain,
access_request_parent1 | access_request_parent2,
&layer_masks_parent1, LANDLOCK_KEY_INODE);
if (is_access_to_paths_allowed(subject->domain, new_dir,
access_request_parent1,
&layer_masks_parent1, &request1,
NULL, 0, NULL, NULL, NULL))
return 0;
landlock_log_denial(subject, &request1);
return -EACCES;
}
access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER;
access_request_parent2 |= LANDLOCK_ACCESS_FS_REFER;
/* Saves the common mount point. */
mnt_dir.mnt = new_dir->mnt;
mnt_dir.dentry = new_dir->mnt->mnt_root;
/*
* old_dentry may be the root of the common mount point and
* !IS_ROOT(old_dentry) at the same time (e.g. with open_tree() and
* OPEN_TREE_CLONE). We do not need to call dget(old_parent) because
* we keep a reference to old_dentry.
*/
old_parent = (old_dentry == mnt_dir.dentry) ? old_dentry :
old_dentry->d_parent;
/* new_dir->dentry is equal to new_dentry->d_parent */
allow_parent1 = collect_domain_accesses(subject->domain, mnt_dir.dentry,
old_parent,
&layer_masks_parent1);
allow_parent2 = collect_domain_accesses(subject->domain, mnt_dir.dentry,
new_dir->dentry,
&layer_masks_parent2);
if (allow_parent1 && allow_parent2)
return 0;
/*
* To be able to compare source and destination domain access rights,
* take into account the @old_dentry access rights aggregated with its
* parent access rights. This will be useful to compare with the
* destination parent access rights.
*/
if (is_access_to_paths_allowed(
subject->domain, &mnt_dir, access_request_parent1,
&layer_masks_parent1, &request1, old_dentry,
access_request_parent2, &layer_masks_parent2, &request2,
exchange ? new_dentry : NULL))
return 0;
if (request1.access) {
request1.audit.u.path.dentry = old_parent;
landlock_log_denial(subject, &request1);
}
if (request2.access) {
request2.audit.u.path.dentry = new_dir->dentry;
landlock_log_denial(subject, &request2);
}
/*
* This prioritizes EACCES over EXDEV for all actions, including
* renames with RENAME_EXCHANGE.
*/
if (likely(is_eacces(&layer_masks_parent1, access_request_parent1) ||
is_eacces(&layer_masks_parent2, access_request_parent2)))
return -EACCES;
/*
* Gracefully forbids reparenting if the destination directory
* hierarchy is not a superset of restrictions of the source directory
* hierarchy, or if LANDLOCK_ACCESS_FS_REFER is not allowed by the
* source or the destination.
*/
return -EXDEV;
}
/* Inode hooks */
static void hook_inode_free_security_rcu(void *inode_security)
{
struct landlock_inode_security *inode_sec;
/*
* All inodes must already have been untied from their object by
* release_inode() or hook_sb_delete().
*/
inode_sec = inode_security + landlock_blob_sizes.lbs_inode;
WARN_ON_ONCE(inode_sec->object);
}
/* Super-block hooks */
/*
* Release the inodes used in a security policy.
*
* Cf. fsnotify_unmount_inodes() and evict_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 (!icount_read_once(inode))
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_state_read(inode) &
(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 there are at least two references
* on the inode.
*/
iput_not_last(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));
}
static void
log_fs_change_topology_path(const struct landlock_cred_security *const subject,
size_t handle_layer, const struct path *const path)
{
landlock_log_denial(subject, &(struct landlock_request) {
.type = LANDLOCK_REQUEST_FS_CHANGE_TOPOLOGY,
.audit = {
.type = LSM_AUDIT_DATA_PATH,
.u.path = *path,
},
.layer_plus_one = handle_layer + 1,
});
}
static void log_fs_change_topology_dentry(
const struct landlock_cred_security *const subject, size_t handle_layer,
struct dentry *const dentry)
{
landlock_log_denial(subject, &(struct landlock_request) {
.type = LANDLOCK_REQUEST_FS_CHANGE_TOPOLOGY,
.audit = {
.type = LSM_AUDIT_DATA_DENTRY,
.u.dentry = dentry,
},
.layer_plus_one = handle_layer + 1,
});
}
/*
* Because a Landlock security policy is defined according to the filesystem
* topology (i.e. the mount namespace), changing it may grant access to files
* not previously allowed.
*
* To make it simple, deny any filesystem topology 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 flag).
*/
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)
{
size_t handle_layer;
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), any_fs,
&handle_layer);
if (!subject)
return 0;
log_fs_change_topology_path(subject, handle_layer, path);
return -EPERM;
}
static int hook_move_mount(const struct path *const from_path,
const struct path *const to_path)
{
size_t handle_layer;
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), any_fs,
&handle_layer);
if (!subject)
return 0;
log_fs_change_topology_path(subject, handle_layer, to_path);
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)
{
size_t handle_layer;
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), any_fs,
&handle_layer);
if (!subject)
return 0;
log_fs_change_topology_dentry(subject, handle_layer, mnt->mnt_root);
return -EPERM;
}
static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
{
size_t handle_layer;
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), any_fs,
&handle_layer);
if (!subject)
return 0;
log_fs_change_topology_dentry(subject, handle_layer, sb->s_root);
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)
{
size_t handle_layer;
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(current_cred(), any_fs,
&handle_layer);
if (!subject)
return 0;
log_fs_change_topology_path(subject, handle_layer, new_path);
return -EPERM;
}
/* Path hooks */
static int hook_path_link(struct dentry *const old_dentry,
const struct path *const new_dir,
struct dentry *const new_dentry)
{
return current_check_refer_path(old_dentry, new_dir, new_dentry, false,
false, false);
}
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 unsigned int flags)
{
/* old_dir refers to old_dentry->d_parent and new_dir->mnt */
return current_check_refer_path(old_dentry, new_dir, new_dentry, true,
!!(flags & RENAME_EXCHANGE),
!!(flags & RENAME_WHITEOUT));
}
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)
{
return current_check_access_path(
dir, get_mode_access(mode, new_decode_dev(dev)));
}
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);
}
static int hook_path_truncate(const struct path *const path)
{
return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE);
}
/**
* unmask_scoped_access - Remove access right bits in @masks in all layers
* where @client and @server have the same domain
*
* This does the same as domain_is_scoped(), but unmasks bits in @masks.
* It can not return early as domain_is_scoped() does.
*
* A scoped access for a given access right bit is allowed iff, for all layer
* depths where the access bit is set, the client and server domain are the
* same. This function clears the access rights @access in @masks at all layer
* depths where the client and server domain are the same, so that, when they
* are all cleared, the access is allowed.
*
* @client: Client domain
* @server: Server domain
* @masks: Layer access masks to unmask
* @access: Access bits that control scoping
*/
static void unmask_scoped_access(const struct landlock_ruleset *const client,
const struct landlock_ruleset *const server,
struct layer_masks *const masks,
const access_mask_t access)
{
int client_layer, server_layer;
const struct landlock_hierarchy *client_walker, *server_walker;
/* This should not happen. */
if (WARN_ON_ONCE(!client))
return;
/* Server has no Landlock domain; nothing to clear. */
if (!server)
return;
/*
* client_layer must be able to represent all numbers from
* LANDLOCK_MAX_NUM_LAYERS - 1 to -1 for the loop below to terminate.
* (It must be large enough, and it must be signed.)
*/
BUILD_BUG_ON(!is_signed_type(typeof(client_layer)));
BUILD_BUG_ON(LANDLOCK_MAX_NUM_LAYERS - 1 >
type_max(typeof(client_layer)));
client_layer = client->num_layers - 1;
client_walker = client->hierarchy;
server_layer = server->num_layers - 1;
server_walker = server->hierarchy;
/*
* Clears the access bits at all layers where the client domain is the
* same as the server domain. We start the walk at min(client_layer,
* server_layer). The layer bits until there can not be cleared because
* either the client or the server domain is missing.
*/
for (; client_layer > server_layer; client_layer--)
client_walker = client_walker->parent;
for (; server_layer > client_layer; server_layer--)
server_walker = server_walker->parent;
for (; client_layer >= 0; client_layer--) {
if (masks->layers[client_layer].access & access &&
client_walker == server_walker)
masks->layers[client_layer].access &= ~access;
client_walker = client_walker->parent;
server_walker = server_walker->parent;
}
}
static int hook_unix_find(const struct path *const path, struct sock *other,
int flags)
{
const struct landlock_ruleset *dom_other;
const struct landlock_cred_security *subject;
struct layer_masks layer_masks;
struct landlock_request request = {};
static const struct access_masks fs_resolve_unix = {
.fs = LANDLOCK_ACCESS_FS_RESOLVE_UNIX,
};
/* Lookup for the purpose of saving coredumps is OK. */
if (unlikely(flags & SOCK_COREDUMP))
return 0;
subject = landlock_get_applicable_subject(current_cred(),
fs_resolve_unix, NULL);
if (!subject)
return 0;
/*
* Ignoring return value: that the domains apply was already checked in
* landlock_get_applicable_subject() above.
*/
landlock_init_layer_masks(subject->domain, fs_resolve_unix.fs,
&layer_masks, LANDLOCK_KEY_INODE);
/* Checks the layers in which we are connecting within the same domain. */
unix_state_lock(other);
if (unlikely(sock_flag(other, SOCK_DEAD) || !other->sk_socket ||
!other->sk_socket->file)) {
unix_state_unlock(other);
/*
* We rely on the caller to catch the (non-reversible) SOCK_DEAD
* condition and retry the lookup. If we returned an error
* here, the lookup would not get retried.
*/
return 0;
}
dom_other = landlock_cred(other->sk_socket->file->f_cred)->domain;
/* Access to the same (or a lower) domain is always allowed. */
unmask_scoped_access(subject->domain, dom_other, &layer_masks,
fs_resolve_unix.fs);
unix_state_unlock(other);
/* Checks the connections to allow-listed paths. */
if (is_access_to_paths_allowed(subject->domain, path,
fs_resolve_unix.fs, &layer_masks,
&request, NULL, 0, NULL, NULL, NULL))
return 0;
landlock_log_denial(subject, &request);
return -EACCES;
}
/* File hooks */
/**
* get_required_file_open_access - Get access needed to open a file
*
* @file: File being opened.
*
* Return: The access rights that are required for opening the given file,
* depending on the file type and open mode.
*/
static access_mask_t
get_required_file_open_access(const struct file *const file)
{
access_mask_t 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_alloc_security(struct file *const file)
{
/*
* Grants all access rights, even if most of them are not checked later
* on. It is more consistent.
*
* Notably, file descriptors for regular files can also be acquired
* without going through the file_open hook, for example when using
* memfd_create(2).
*/
landlock_file(file)->allowed_access = LANDLOCK_MASK_ACCESS_FS;
return 0;
}
static bool is_device(const struct file *const file)
{
const struct inode *inode = file_inode(file);
return S_ISBLK(inode->i_mode) || S_ISCHR(inode->i_mode);
}
static int hook_file_open(struct file *const file)
{
struct layer_masks layer_masks = {};
access_mask_t open_access_request, full_access_request, allowed_access,
optional_access;
const struct landlock_cred_security *const subject =
landlock_get_applicable_subject(file->f_cred, any_fs, NULL);
struct landlock_request request = {};
if (!subject)
return 0;
/*
* Because a file may be opened with O_PATH, get_required_file_open_access()
* may return 0. This case will be handled with a future Landlock
* evolution.
*/
open_access_request = get_required_file_open_access(file);
/*
* We look up more access than what we immediately need for open(), so
* that we can later authorize operations on opened files.
*/
optional_access = LANDLOCK_ACCESS_FS_TRUNCATE;
if (is_device(file))
optional_access |= LANDLOCK_ACCESS_FS_IOCTL_DEV;
full_access_request = open_access_request | optional_access;
if (is_access_to_paths_allowed(
subject->domain, &file->f_path,
landlock_init_layer_masks(subject->domain,
full_access_request, &layer_masks,
LANDLOCK_KEY_INODE),
&layer_masks, &request, NULL, 0, NULL, NULL, NULL)) {
allowed_access = full_access_request;
} else {
/*
* Calculate the actual allowed access rights from layer_masks.
* Remove the access rights from the full access request which
* are still unfulfilled in any of the layers.
*/
allowed_access = full_access_request;
for (size_t i = 0; i < ARRAY_SIZE(layer_masks.layers); i++)
allowed_access &= ~layer_masks.layers[i].access;
}
/*
* For operations on already opened files (i.e. ftruncate()), it is the
* access rights at the time of open() which decide whether the
* operation is permitted. Therefore, we record the relevant subset of
* file access rights in the opened struct file.
*/
landlock_file(file)->allowed_access = allowed_access;
#ifdef CONFIG_AUDIT
landlock_file(file)->deny_masks = landlock_get_deny_masks(
_LANDLOCK_ACCESS_FS_OPTIONAL, optional_access, &layer_masks);
landlock_file(file)->quiet_optional_accesses =
landlock_get_quiet_optional_accesses(
_LANDLOCK_ACCESS_FS_OPTIONAL,
landlock_file(file)->deny_masks, &layer_masks);
#endif /* CONFIG_AUDIT */
if (access_mask_subset(open_access_request, allowed_access))
return 0;
/* Sets access to reflect the actual request. */
request.access = open_access_request;
landlock_log_denial(subject, &request);
return -EACCES;
}
static int hook_file_truncate(struct file *const file)
{
/*
* Allows truncation if the truncate right was available at the time of
* opening the file, to get a consistent access check as for read, write
* and execute operations.
*
* Note: For checks done based on the file's Landlock allowed access, we
* enforce them independently of whether the current thread is in a
* Landlock domain, so that open files passed between independent
* processes retain their behaviour.
*/
if (landlock_file(file)->allowed_access & LANDLOCK_ACCESS_FS_TRUNCATE)
return 0;
landlock_log_denial(landlock_cred(file->f_cred), &(struct landlock_request) {
.type = LANDLOCK_REQUEST_FS_ACCESS,
.audit = {
.type = LSM_AUDIT_DATA_FILE,
.u.file = file,
},
.all_existing_optional_access = _LANDLOCK_ACCESS_FS_OPTIONAL,
.access = LANDLOCK_ACCESS_FS_TRUNCATE,
#ifdef CONFIG_AUDIT
.deny_masks = landlock_file(file)->deny_masks,
.quiet_optional_accesses = landlock_file(file)->quiet_optional_accesses,
#endif /* CONFIG_AUDIT */
});
return -EACCES;
}
static int hook_file_ioctl_common(const struct file *const file,
const unsigned int cmd, const bool is_compat)
{
access_mask_t allowed_access = landlock_file(file)->allowed_access;
/*
* It is the access rights at the time of opening the file which
* determine whether IOCTL can be used on the opened file later.
*
* The access right is attached to the opened file in hook_file_open().
*/
if (allowed_access & LANDLOCK_ACCESS_FS_IOCTL_DEV)
return 0;
if (!is_device(file))
return 0;
if (unlikely(is_compat) ? is_masked_device_ioctl_compat(cmd) :
is_masked_device_ioctl(cmd))
return 0;
landlock_log_denial(landlock_cred(file->f_cred), &(struct landlock_request) {
.type = LANDLOCK_REQUEST_FS_ACCESS,
.audit = {
.type = LSM_AUDIT_DATA_IOCTL_OP,
.u.op = &(struct lsm_ioctlop_audit) {
.path = file->f_path,
.cmd = cmd,
},
},
.all_existing_optional_access = _LANDLOCK_ACCESS_FS_OPTIONAL,
.access = LANDLOCK_ACCESS_FS_IOCTL_DEV,
#ifdef CONFIG_AUDIT
.deny_masks = landlock_file(file)->deny_masks,
.quiet_optional_accesses = landlock_file(file)->quiet_optional_accesses,
#endif /* CONFIG_AUDIT */
});
return -EACCES;
}
static int hook_file_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
return hook_file_ioctl_common(file, cmd, false);
}
static int hook_file_ioctl_compat(struct file *file, unsigned int cmd,
unsigned long arg)
{
return hook_file_ioctl_common(file, cmd, true);
}
/*
* Always allow sending signals between threads of the same process. This
* ensures consistency with hook_task_kill().
*/
static bool control_current_fowner(struct fown_struct *const fown)
{
struct task_struct *p;
/*
* Lock already held by __f_setown(), see commit 26f204380a3c ("fs: Fix
* file_set_fowner LSM hook inconsistencies").
*/
lockdep_assert_held(&fown->lock);
/*
* A process-group or session owner (PIDTYPE_PGID/PIDTYPE_SID) fans the
* signal out to every member at delivery time, so record the domain and
* let hook_file_send_sigiotask() check the live scope per recipient.
*/
if (fown->pid_type != PIDTYPE_PID && fown->pid_type != PIDTYPE_TGID)
return true;
/*
* Some callers (e.g. fcntl_dirnotify) may not be in an RCU read-side
* critical section.
*/
guard(rcu)();
p = pid_task(fown->pid, fown->pid_type);
if (!p)
return true;
return !same_thread_group(p, current);
}
static void hook_file_set_fowner(struct file *file)
{
struct landlock_ruleset *prev_dom;
struct landlock_cred_security fown_subject = {};
struct pid *prev_tg, *fown_tg = NULL;
size_t fown_layer = 0;
if (control_current_fowner(file_f_owner(file))) {
static const struct access_masks signal_scope = {
.scope = LANDLOCK_SCOPE_SIGNAL,
};
const struct landlock_cred_security *new_subject =
landlock_get_applicable_subject(
current_cred(), signal_scope, &fown_layer);
if (new_subject) {
landlock_get_ruleset(new_subject->domain);
fown_subject = *new_subject;
fown_tg = get_pid(task_tgid(current));
}
}
prev_dom = landlock_file(file)->fown_subject.domain;
prev_tg = landlock_file(file)->fown_tg;
landlock_file(file)->fown_subject = fown_subject;
landlock_file(file)->fown_tg = fown_tg;
#ifdef CONFIG_AUDIT
landlock_file(file)->fown_layer = fown_layer;
#endif /* CONFIG_AUDIT*/
/* May be called in an RCU read-side critical section. */
landlock_put_ruleset_deferred(prev_dom);
put_pid(prev_tg);
}
static void hook_file_free_security(struct file *file)
{
put_pid(landlock_file(file)->fown_tg);
landlock_put_ruleset_deferred(landlock_file(file)->fown_subject.domain);
}
static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(inode_free_security_rcu, hook_inode_free_security_rcu),
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(path_truncate, hook_path_truncate),
LSM_HOOK_INIT(unix_find, hook_unix_find),
LSM_HOOK_INIT(file_alloc_security, hook_file_alloc_security),
LSM_HOOK_INIT(file_open, hook_file_open),
LSM_HOOK_INIT(file_truncate, hook_file_truncate),
LSM_HOOK_INIT(file_ioctl, hook_file_ioctl),
LSM_HOOK_INIT(file_ioctl_compat, hook_file_ioctl_compat),
LSM_HOOK_INIT(file_set_fowner, hook_file_set_fowner),
LSM_HOOK_INIT(file_free_security, hook_file_free_security),
};
__init void landlock_add_fs_hooks(void)
{
security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
&landlock_lsmid);
}
#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
/* clang-format off */
static struct kunit_case test_cases[] = {
KUNIT_CASE(test_no_more_access),
KUNIT_CASE(test_scope_to_request_with_exec_none),
KUNIT_CASE(test_scope_to_request_with_exec_some),
KUNIT_CASE(test_scope_to_request_without_access),
KUNIT_CASE(test_is_eacces_with_none),
KUNIT_CASE(test_is_eacces_with_refer),
KUNIT_CASE(test_is_eacces_with_write),
{}
};
/* clang-format on */
static struct kunit_suite test_suite = {
.name = "landlock_fs",
.test_cases = test_cases,
};
kunit_test_suite(test_suite);
#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
