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landlock: Allow FS topology changes for domains without such rule type

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Allow mount point and root directory changes when there is no filesystem
rule tied to the current Landlock domain. This doesn't change anything
for now because a domain must have at least a (filesystem) rule, but
this will change when other rule types will come. For instance, a domain
only restricting the network should have no impact on filesystem
restrictions.

Add a new get_current_fs_domain() helper to quickly check filesystem
rule existence for all filesystem LSM hooks.

Remove unnecessary inlining.

Link: https://lore.kernel.org/r/20231026014751.414649-3-konstantin.meskhidze@huawei.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
This commit is contained in:
Mickaël Salaün 2023-10-26 09:47:41 +08:00
parent 13fc6455fa
commit d722036403
No known key found for this signature in database
GPG key ID: E5E3D0E88C82F6D2
4 changed files with 63 additions and 43 deletions
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6
Documentation/userspace-api/landlock.rst
View file

@ -387,9 +387,9 @@ Current limitations
Filesystem topology modification
--------------------------------
As for file renaming and linking, a sandboxed thread cannot modify its
filesystem topology, whether via :manpage:`mount(2)` or
:manpage:`pivot_root(2)`. However, :manpage:`chroot(2)` calls are not denied.
Threads sandboxed with filesystem restrictions cannot modify filesystem
topology, whether via :manpage:`mount(2)` or :manpage:`pivot_root(2)`.
However, :manpage:`chroot(2)` calls are not denied.
Special filesystems
-------------------

74
security/landlock/fs.c
View file

@ -150,16 +150,6 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
LANDLOCK_ACCESS_FS_TRUNCATE)
/* clang-format on */
/*
* All access rights that are denied by default whether they are handled or not
* by a ruleset/layer. This must be ORed with all ruleset->fs_access_masks[]
* entries when we need to get the absolute handled access masks.
*/
/* clang-format off */
#define ACCESS_INITIALLY_DENIED ( \
LANDLOCK_ACCESS_FS_REFER)
/* clang-format on */
/*
* @path: Should have been checked by get_path_from_fd().
*/
@ -179,8 +169,7 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
/* Transforms relative access rights to absolute ones. */
access_rights |= LANDLOCK_MASK_ACCESS_FS &
~(landlock_get_fs_access_mask(ruleset, 0) |
ACCESS_INITIALLY_DENIED);
~landlock_get_fs_access_mask(ruleset, 0);
object = get_inode_object(d_backing_inode(path->dentry));
if (IS_ERR(object))
return PTR_ERR(object);
@ -287,15 +276,16 @@ static inline bool is_nouser_or_private(const struct dentry *dentry)
unlikely(IS_PRIVATE(d_backing_inode(dentry))));
}
static inline access_mask_t
get_handled_accesses(const struct landlock_ruleset *const domain)
static access_mask_t
get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
{
access_mask_t access_dom = ACCESS_INITIALLY_DENIED;
access_mask_t access_dom = 0;
size_t layer_level;
for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
access_dom |= landlock_get_fs_access_mask(domain, layer_level);
return access_dom & LANDLOCK_MASK_ACCESS_FS;
access_dom |=
landlock_get_raw_fs_access_mask(domain, layer_level);
return access_dom;
}
/**
@ -331,13 +321,8 @@ init_layer_masks(const struct landlock_ruleset *const domain,
for_each_set_bit(access_bit, &access_req,
ARRAY_SIZE(*layer_masks)) {
/*
* Artificially handles all initially denied by default
* access rights.
*/
if (BIT_ULL(access_bit) &
(landlock_get_fs_access_mask(domain, layer_level) |
ACCESS_INITIALLY_DENIED)) {
landlock_get_fs_access_mask(domain, layer_level)) {
(*layer_masks)[access_bit] |=
BIT_ULL(layer_level);
handled_accesses |= BIT_ULL(access_bit);
@ -347,6 +332,25 @@ init_layer_masks(const struct landlock_ruleset *const domain,
return handled_accesses;
}
static access_mask_t
get_handled_fs_accesses(const struct landlock_ruleset *const domain)
{
/* Handles all initially denied by default access rights. */
return get_raw_handled_fs_accesses(domain) |
LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
}
static const struct landlock_ruleset *get_current_fs_domain(void)
{
const struct landlock_ruleset *const dom =
landlock_get_current_domain();
if (!dom || !get_raw_handled_fs_accesses(dom))
return NULL;
return dom;
}
/*
* Check that a destination file hierarchy has more restrictions than a source
* file hierarchy. This is only used for link and rename actions.
@ -519,7 +523,7 @@ static bool is_access_to_paths_allowed(
* a superset of the meaningful requested accesses).
*/
access_masked_parent1 = access_masked_parent2 =
get_handled_accesses(domain);
get_handled_fs_accesses(domain);
is_dom_check = true;
} else {
if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
@ -651,8 +655,7 @@ static inline int check_access_path(const struct landlock_ruleset *const domain,
static inline int current_check_access_path(const struct path *const path,
const access_mask_t access_request)
{
const struct landlock_ruleset *const dom =
landlock_get_current_domain();
const struct landlock_ruleset *const dom = get_current_fs_domain();
if (!dom)
return 0;
@ -815,8 +818,7 @@ static int current_check_refer_path(struct dentry *const old_dentry,
struct dentry *const new_dentry,
const bool removable, const bool exchange)
{
const struct landlock_ruleset *const dom =
landlock_get_current_domain();
const struct landlock_ruleset *const dom = get_current_fs_domain();
bool allow_parent1, allow_parent2;
access_mask_t access_request_parent1, access_request_parent2;
struct path mnt_dir;
@ -1050,7 +1052,7 @@ 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())
if (!get_current_fs_domain())
return 0;
return -EPERM;
}
@ -1058,7 +1060,7 @@ static int hook_sb_mount(const char *const dev_name,
static int hook_move_mount(const struct path *const from_path,
const struct path *const to_path)
{
if (!landlock_get_current_domain())
if (!get_current_fs_domain())
return 0;
return -EPERM;
}
@ -1069,14 +1071,14 @@ static int hook_move_mount(const struct path *const from_path,
*/
static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
{
if (!landlock_get_current_domain())
if (!get_current_fs_domain())
return 0;
return -EPERM;
}
static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
{
if (!landlock_get_current_domain())
if (!get_current_fs_domain())
return 0;
return -EPERM;
}
@ -1092,7 +1094,7 @@ static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
static int hook_sb_pivotroot(const struct path *const old_path,
const struct path *const new_path)
{
if (!landlock_get_current_domain())
if (!get_current_fs_domain())
return 0;
return -EPERM;
}
@ -1128,8 +1130,7 @@ 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();
const struct landlock_ruleset *const dom = get_current_fs_domain();
if (!dom)
return 0;
@ -1208,8 +1209,7 @@ static int hook_file_open(struct file *const file)
layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
access_mask_t open_access_request, full_access_request, allowed_access;
const access_mask_t optional_access = LANDLOCK_ACCESS_FS_TRUNCATE;
const struct landlock_ruleset *const dom =
landlock_get_current_domain();
const struct landlock_ruleset *const dom = get_current_fs_domain();
if (!dom)
return 0;

24
security/landlock/ruleset.h
View file

@ -15,10 +15,21 @@
#include <linux/rbtree.h>
#include <linux/refcount.h>
#include <linux/workqueue.h>
#include <uapi/linux/landlock.h>
#include "limits.h"
#include "object.h"
/*
* All access rights that are denied by default whether they are handled or not
* by a ruleset/layer. This must be ORed with all ruleset->access_masks[]
* entries when we need to get the absolute handled access masks.
*/
/* clang-format off */
#define LANDLOCK_ACCESS_FS_INITIALLY_DENIED ( \
LANDLOCK_ACCESS_FS_REFER)
/* clang-format on */
typedef u16 access_mask_t;
/* Makes sure all filesystem access rights can be stored. */
static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
@ -196,12 +207,21 @@ landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
}
static inline access_mask_t
landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
return (ruleset->access_masks[layer_level] >>
LANDLOCK_SHIFT_ACCESS_FS) &
LANDLOCK_MASK_ACCESS_FS;
}
static inline access_mask_t
landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
/* Handles all initially denied by default access rights. */
return landlock_get_raw_fs_access_mask(ruleset, layer_level) |
LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
}
#endif /* _SECURITY_LANDLOCK_RULESET_H */

2
security/landlock/syscalls.c
View file

@ -349,7 +349,7 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
* Checks that allowed_access matches the @ruleset constraints
* (ruleset->access_masks[0] is automatically upgraded to 64-bits).
*/
mask = landlock_get_fs_access_mask(ruleset, 0);
mask = landlock_get_raw_fs_access_mask(ruleset, 0);
if ((path_beneath_attr.allowed_access | mask) != mask) {
err = -EINVAL;
goto out_put_ruleset;