[PATCH v12 02/12] landlock: Allow filesystem layout changes for domains without such rule type
Konstantin Meskhidze
konstantin.meskhidze at huawei.com
Wed Sep 20 09:26:30 UTC 2023
From: Mickaël Salaün <mic at digikod.net>
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.
Signed-off-by: Mickaël Salaün <mic at digikod.net>
---
Changes since v11:
* None.
Changes since v10:
* Squashes landlock_get_fs_access_mask() part into commit 1.
* Opportunistically removes inline get_raw_handled_fs_accesses function
with changing it's signature.
Changes since v9:
* Refactors documentaion landlock.rst.
* Changes ACCESS_FS_INITIALLY_DENIED constant
to LANDLOCK_ACCESS_FS_INITIALLY_DENIED.
* Gets rid of unnecessary masking of access_dom in
get_raw_handled_fs_accesses() function.
Changes since v8:
* Refactors get_handled_fs_accesses().
* Adds landlock_get_raw_fs_access_mask() helper.
---
Documentation/userspace-api/landlock.rst | 6 +-
security/landlock/fs.c | 74 ++++++++++++------------
security/landlock/ruleset.h | 25 +++++++-
security/landlock/syscalls.c | 2 +-
4 files changed, 64 insertions(+), 43 deletions(-)
diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index d8cd8cd9ce25..f6a7da21708a 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -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
-------------------
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 6953801619ac..e8d680c2c80a 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -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;
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index e19c7a99dfc6..6e2ad1546ab3 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -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);
@@ -196,11 +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 */
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index 7ec6bbed7117..d35cd5d304db 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -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;
--
2.25.1
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