[PATCH v2 0/2] landlock: Fix TSYNC deadlock and clean up error path

[Yihan Ding <dingyihan@uniontech.com>]

Hello,

This patch series fixes a deadlock in the Landlock TSYNC multithreading 
support, originally reported by syzbot, and cleans up the associated 
interrupt recovery path.

The deadlock occurs when multiple threads concurrently call 
landlock_restrict_self() with sibling thread restriction enabled, 
causing them to mutually queue task_works on each other and block 
indefinitely.

* Patch 1 fixes the root cause by serializing the TSYNC operations 
  within the same process using the exec_update_lock.
* Patch 2 cleans up the interrupt recovery path by replacing an 
  unnecessary wait_for_completion() with a straightforward loop break, 
  avoiding Use-After-Free while unblocking remaining task_works.

Changes in v2:
- Split the changes into a 2-patch series for clearer logical separation.
- Patch 1: Adopted down_write_killable() instead of down_write() to 
  ensure responsiveness to fatal signals (suggested by Günther Noack).
- Patch 2: Removed wait_for_completion(&shared_ctx.all_prepared) and 
  replaced it with a `break`. The function's bottom wait for 
  'all_finished' already provides the necessary UAF protection 
  (suggested by Günther Noack).

Link to v1: https://lore.kernel.org/all/20260224062729.2908692-1-dingyihan@uniontech.com/

Yihan Ding (2):
  landlock: Serialize TSYNC thread restriction
  landlock: Clean up interrupted thread logic in TSYNC

 security/landlock/tsync.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

-- 
2.51.0