kernel/linux.git/security/landlock/tsync.c, branch v7.0-rc7

landlock: Clean up interrupted thread logic in TSYNC

2026-03-10T17:22:58+00:00

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 Signed-off-by: Yihan Ding Tested-by: Günther Noack Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20260306021651.744723-3-dingyihan@uniontech.com Signed-off-by: Mickaël Salaün

landlock: Serialize TSYNC thread restriction

2026-03-10T17:22:56+00:00

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: 42fc7e6543f6 ("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 Suggested-by: Tingmao Wang Tested-by: Justin Suess Signed-off-by: Yihan Ding Tested-by: Günther Noack Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20260306021651.744723-2-dingyihan@uniontech.com Signed-off-by: Mickaël Salaün

landlock: Improve TSYNC types

2026-03-04T17:28:11+00:00

Constify pointers when it makes sense. Consistently use size_t for loops, especially to match works->size type. Add new lines to improve readability. Cc: Jann Horn Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20260217122341.2359582-2-mic@digikod.net Signed-off-by: Mickaël Salaün

landlock: Fully release unused TSYNC work entries

2026-03-04T17:28:10+00:00

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 Reviewed-by: Günther Noack Link: https://lore.kernel.org/r/20260217122341.2359582-1-mic@digikod.net [mic: Replace memset() with compound literal] Signed-off-by: Mickaël Salaün

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

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

landlock: Multithreading support for landlock_restrict_self()

2026-02-06T16:54:37+00:00

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 Cc: John Johansen Cc: Paul Moore Suggested-by: Jann Horn Signed-off-by: Günther Noack 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