The BUILD_BUG_ON check in domain_is_scoped() and
unmask_scoped_access() should check that the loop that counts down
client_layer finishes. We therefore check that the numbers
LANDLOCK_MAX_NUM_LAYERS-1 and -1 are both representable by that
integer. If they are representable, the numbers in between are
representable too, and the loop finishes.
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260327164838.38231-6-gnoack3000@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
* Add a new access right LANDLOCK_ACCESS_FS_RESOLVE_UNIX, which
controls the lookup operations for named UNIX domain sockets. The
resolution happens during connect() and sendmsg() (depending on
socket type).
* Change access_mask_t from u16 to u32 (see below)
* Hook into the path lookup in unix_find_bsd() in af_unix.c, using a
LSM hook. Make policy decisions based on the new access rights
* Increment the Landlock ABI version.
* Minor test adaptations to keep the tests working.
* Document the design rationale for scoped access rights,
and cross-reference it from the header documentation.
With this access right, access is granted if either of the following
conditions is met:
* The target socket's filesystem path was allow-listed using a
LANDLOCK_RULE_PATH_BENEATH rule, *or*:
* The target socket was created in the same Landlock domain in which
LANDLOCK_ACCESS_FS_RESOLVE_UNIX was restricted.
In case of a denial, connect() and sendmsg() return EACCES, which is
the same error as it is returned if the user does not have the write
bit in the traditional UNIX file system permissions of that file.
The access_mask_t type grows from u16 to u32 to make space for the new
access right. This also doubles the size of struct layer_access_masks
from 32 byte to 64 byte. To avoid memory layout inconsistencies between
architectures (especially m68k), pack and align struct access_masks [2].
Document the (possible future) interaction between scoped flags and
other access rights in struct landlock_ruleset_attr, and summarize the
rationale, as discussed in code review leading up to [3].
This feature was created with substantial discussion and input from
Justin Suess, Tingmao Wang and Mickaël Salaün.
Cc: Tingmao Wang <m@maowtm.org>
Cc: Justin Suess <utilityemal77@gmail.com>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Suggested-by: Jann Horn <jannh@google.com>
Link[1]: https://github.com/landlock-lsm/linux/issues/36
Link[2]: https://lore.kernel.org/all/20260401.Re1Eesu1Yaij@digikod.net/
Link[3]: https://lore.kernel.org/all/20260205.8531e4005118@gnoack.org/
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20260327164838.38231-5-gnoack3000@gmail.com
[mic: Fix kernel-doc formatting, pack and align access_masks]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
The insert_rule() and create_rule() functions take a
pointer-to-flexible-array parameter declared as:
const struct landlock_layer (*const layers)[]
The kernel-doc parser cannot handle a qualifier between * and the
parameter name in this syntax, producing spurious "Invalid param" and
"not described" warnings.
Remove the const qualifier of the "layers" argument to avoid this
parsing issue.
Cc: Günther Noack <gnoack@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260310172004.1839864-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
The canonical kernel-doc form is "Return:" (singular, without trailing
"s"). Normalize all existing "Returns:" occurrences across the Landlock
source tree to the canonical form.
Also fix capitalization for consistency. Balance descriptions to
describe all possible returned values.
Consolidate bullet-point return descriptions into inline text for
functions with simple two-value or three-value returns for consistency.
Cc: Günther Noack <gnoack@google.com>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260304193134.250495-3-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
The kernel-doc -Wreturn check warns about functions with documentation
comments that lack a "Return:" section. Add "Return:" documentation to
all functions missing it so that kernel-doc -Wreturn passes cleanly.
Convert existing function descriptions into a formal "Return:" section.
Also fix the inaccurate return documentation for
landlock_merge_ruleset() which claimed to return @parent directly, and
document the previously missing ERR_PTR() error return path. Document
the ABI version and errata return paths for landlock_create_ruleset()
which were previously only implied by the prose.
Cc: Günther Noack <gnoack@google.com>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260304193134.250495-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
LANDLOCK_RESTRICT_SELF_TSYNC does not allow
LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF with ruleset_fd=-1, preventing
a multithreaded process from atomically propagating subdomain log muting
to all threads without creating a domain layer. Relax the fd=-1
condition to accept TSYNC alongside LOG_SUBDOMAINS_OFF, and update the
documentation accordingly.
Add flag validation tests for all TSYNC combinations with ruleset_fd=-1,
and audit tests verifying both transition directions: muting via TSYNC
(logged to not logged) and override via TSYNC (not logged to logged).
Cc: Günther Noack <gnoack@google.com>
Cc: stable@vger.kernel.org
Fixes: 42fc7e6543 ("landlock: Multithreading support for landlock_restrict_self()")
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260407164107.2012589-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
hook_cred_transfer() only copies the Landlock security blob when the
source credential has a domain. This is inconsistent with
landlock_restrict_self() which can set LOG_SUBDOMAINS_OFF on a
credential without creating a domain (via the ruleset_fd=-1 path): the
field is committed but not preserved across fork() because the child's
prepare_creds() calls hook_cred_transfer() which skips the copy when
domain is NULL.
This breaks the documented use case where a process mutes subdomain logs
before forking sandboxed children: the children lose the muting and
their domains produce unexpected audit records.
Fix this by unconditionally copying the Landlock credential blob.
Cc: Günther Noack <gnoack@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: stable@vger.kernel.org
Fixes: ead9079f75 ("landlock: Add LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF")
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260407164107.2012589-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
In landlock_restrict_sibling_threads(), when the calling thread is
interrupted while waiting for sibling threads to prepare, it executes
a recovery path.
Previously, this path included a wait_for_completion() call on
all_prepared to prevent a Use-After-Free of the local shared_ctx.
However, this wait is redundant. Exiting the main do-while loop
already leads to a bottom cleanup section that unconditionally waits
for all_finished. Therefore, replacing the wait with a simple break
is safe, prevents UAF, and correctly unblocks the remaining task_works.
Clean up the error path by breaking the loop and updating the
surrounding comments to accurately reflect the state machine.
Suggested-by: Günther Noack <gnoack3000@gmail.com>
Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
Tested-by: Günther Noack <gnoack3000@gmail.com>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260306021651.744723-3-dingyihan@uniontech.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
syzbot found a deadlock in landlock_restrict_sibling_threads().
When multiple threads concurrently call landlock_restrict_self() with
sibling thread restriction enabled, they can deadlock by mutually
queueing task_works on each other and then blocking in kernel space
(waiting for the other to finish).
Fix this by serializing the TSYNC operations within the same process
using the exec_update_lock. This prevents concurrent invocations
from deadlocking.
We use down_write_trylock() and restart the syscall if the lock
cannot be acquired immediately. This ensures that if a thread fails
to get the lock, it will return to userspace, allowing it to process
any pending TSYNC task_works from the lock holder, and then
transparently restart the syscall.
Fixes: 42fc7e6543 ("landlock: Multithreading support for landlock_restrict_self()")
Reported-by: syzbot+7ea2f5e9dfd468201817@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7ea2f5e9dfd468201817
Suggested-by: Günther Noack <gnoack3000@gmail.com>
Suggested-by: Tingmao Wang <m@maowtm.org>
Tested-by: Justin Suess <utilityemal77@gmail.com>
Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
Tested-by: Günther Noack <gnoack3000@gmail.com>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260306021651.744723-2-dingyihan@uniontech.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
If task_work_add() failed, ctx->task is put but the tsync_works struct
is not reset to its previous state. The first consequence is that the
kernel allocates memory for dying threads, which could lead to
user-accounted memory exhaustion (not very useful nor specific to this
case). The second consequence is that task_work_cancel(), called by
cancel_tsync_works(), can dereference a NULL task pointer.
Fix this issues by keeping a consistent works->size wrt the added task
work. This is done in a new tsync_works_trim() helper which also cleans
up the shared_ctx and work fields.
As a safeguard, add a pointer check to cancel_tsync_works() and update
tsync_works_release() accordingly.
Cc: Jann Horn <jannh@google.com>
Reviewed-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20260217122341.2359582-1-mic@digikod.net
[mic: Replace memset() with compound literal]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
This is the exact same thing as the 'alloc_obj()' version, only much
smaller because there are a lot fewer users of the *alloc_flex()
interface.
As with alloc_obj() version, this was done entirely with mindless brute
force, using the same script, except using 'flex' in the pattern rather
than 'objs*'.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
The layer masks data structure tracks the requested but unfulfilled
access rights during an operation's security check. It stores one bit
for each combination of access right and layer index. If the bit is
set, that access right is not granted (yet) in the given layer and we
have to traverse the path further upwards to grant it.
Previously, the layer masks were stored as arrays mapping from access
right indices to layer_mask_t. The layer_mask_t value then indicates
all layers in which the given access right is still (tentatively)
denied.
This patch introduces struct layer_access_masks instead: This struct
contains an array with the access_mask_t of each (tentatively) denied
access right in that layer.
The hypothesis of this patch is that this simplifies the code enough
so that the resulting code will run faster:
* We can use bitwise operations in multiple places where we previously
looped over bits individually with macros. (Should require less
branch speculation and lends itself to better loop unrolling.)
* Code is ~75 lines smaller.
Other noteworthy changes:
* In no_more_access(), call a new helper function may_refer(), which
only solves the asymmetric case. Previously, the code interleaved
the checks for the two symmetric cases in RENAME_EXCHANGE. It feels
that the code is clearer when renames without RENAME_EXCHANGE are
more obviously the normal case.
Tradeoffs:
This change improves performance, at a slight size increase to the
layer masks data structure.
This fixes the size of the data structure at 32 bytes for all types of
access rights. (64, once we introduce a 17th filesystem access right).
For filesystem access rights, at the moment, the data structure has
the same size as before, but once we introduce the 17th filesystem
access right, it will double in size (from 32 to 64 bytes), as
access_mask_t grows from 16 to 32 bit [1].
Link: https://lore.kernel.org/all/20260120.haeCh4li9Vae@digikod.net/ [1]
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260206151154.97915-5-gnoack3000@gmail.com
[mic: Cosmetic fixes, moved struct layer_access_masks definition]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Add errata section with code examples for querying errata and a warning
that most applications should not check errata. Use kernel-doc directives
to include errata descriptions from the header files instead of manual
links.
Also enhance existing DOC sections in security/landlock/errata/abi-*.h
files with Impact sections, and update the code comment in syscalls.c
to remind developers to update errata documentation when applicable.
This addresses the gap where the kernel implements errata tracking
but provides no user-facing documentation on how to use it, while
improving the existing technical documentation in-place rather than
duplicating it.
Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20260128031814.2945394-3-samasth.norway.ananda@oracle.com
[mic: Cosmetic fix]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Move the socket type check earlier, so that we will later be able to add
elseifs for other types. Ordering of checks (socket is of a type we
enforce restrictions on) / (current creds have Landlock restrictions)
should not change anything.
Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
Link: https://lore.kernel.org/r/20251212163704.142301-3-matthieu@buffet.re
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Introduce the LANDLOCK_RESTRICT_SELF_TSYNC flag. With this flag, a
given Landlock ruleset is applied to all threads of the calling
process, instead of only the current one.
Without this flag, multithreaded userspace programs currently resort
to using the nptl(7)/libpsx hack for multithreaded policy enforcement,
which is also used by libcap and for setuid(2). Using this
userspace-based scheme, the threads of a process enforce the same
Landlock policy, but the resulting Landlock domains are still
separate. The domains being separate causes multiple problems:
* When using Landlock's "scoped" access rights, the domain identity is
used to determine whether an operation is permitted. As a result,
when using LANLDOCK_SCOPE_SIGNAL, signaling between sibling threads
stops working. This is a problem for programming languages and
frameworks which are inherently multithreaded (e.g. Go).
* In audit logging, the domains of separate threads in a process will
get logged with different domain IDs, even when they are based on
the same ruleset FD, which might confuse users.
Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Paul Moore <paul@paul-moore.com>
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20251127115136.3064948-2-gnoack@google.com
[mic: Fix restrict_self_flags test, clean up Makefile, allign comments,
reduce local variable scope, add missing includes]
Closes: https://github.com/landlock-lsm/linux/issues/2
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Until now, each landlock_request struct were allocated on the stack, even
if not really used, because is_access_to_paths_allowed() unconditionally
modified the passed references. Even if the changed landlock_request
variables are not used, the compiler is not smart enough to detect this
case.
To avoid this issue, explicitly disable the related code when
CONFIG_AUDIT is not set, which enables elision of log_request_parent*
and associated caller's stack variables thanks to dead code elimination.
This makes it possible to reduce the stack frame by 32 bytes for the
path_link and path_rename hooks, and by 20 bytes for most other
filesystem hooks.
Here is a summary of scripts/stackdelta before and after this change
when CONFIG_AUDIT is disabled:
current_check_refer_path 560 320 -240
current_check_access_path 328 184 -144
hook_file_open 328 184 -144
is_access_to_paths_allowed 376 360 -16
Also, add extra pointer checks to be more future-proof.
Cc: Günther Noack <gnoack@google.com>
Reported-by: Tingmao Wang <m@maowtm.org>
Closes: https://lore.kernel.org/r/eb86863b-53b0-460b-b223-84dd31d765b9@maowtm.org
Fixes: 2fc80c69df ("landlock: Log file-related denials")
Link: https://lore.kernel.org/r/20251219142302.744917-2-mic@digikod.net
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
[mic: Improve stack usage measurement accuracy with scripts/stackdelta]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Günther NoackandMickaël Salaün
Yihan DingandMickaël Salaün
Linus Torvalds
Kees Cook
Samasth Norway AnandaandMickaël Salaün
Matthieu BuffetandMickaël Salaün
Günther NoackandMickaël Salaün
Tingmao WangandMickaël Salaün