[PATCH] filelock: fix potential use-after-free in posix_lock_inode

[Jeff Layton]

Light Hsieh reported a KASAN UAF warning in trace_posix_lock_inode().
The request pointer had been changed earlier to point to a lock entry
that was added to the inode's list. However, before the tracepoint could
fire, another task raced in and freed that lock.

Fix this by moving the tracepoint inside the spinlock, which should
ensure that this doesn't happen.

Fixes: 74f6f5912693 ("locks: fix KASAN: use-after-free in trace_event_raw_event_filelock_lock")
Link: https://lore.kernel.org/linux-fsdevel/724ffb0a2962e912ea62bb0515deadf39c325112.camel@kernel.org/
Reported-by: Light Hsieh (謝明燈) <Light.Hsieh at mediatek.com>
Signed-off-by: Jeff Layton <jlayton at kernel.org>
---
 fs/locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/locks.c b/fs/locks.c
index c360d1992d21..bdd94c32256f 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1367,9 +1367,9 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 		locks_wake_up_blocks(&left->c);
 	}
  out:
+	trace_posix_lock_inode(inode, request, error);
 	spin_unlock(&ctx->flc_lock);
 	percpu_up_read(&file_rwsem);
-	trace_posix_lock_inode(inode, request, error);
 	/*
 	 * Free any unused locks.
 	 */

---
base-commit: e9d22f7a6655941fc8b2b942ed354ec780936b3e
change-id: 20240702-filelock-6-10-3fa00ca4fe53

Best regards,
-- 
Jeff Layton <jlayton at kernel.org>