nilfs2-fix-potential-uaf-of-struct-nilfs_sc_info-in-nilfs_segctor_thread.patch removed from -mm tree

The quilt patch titled
Subject: nilfs2: fix potential UAF of struct nilfs_sc_info in nilfs_segctor_thread()
has been removed from the -mm tree. Its filename was
nilfs2-fix-potential-uaf-of-struct-nilfs_sc_info-in-nilfs_segctor_thread.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Ryusuke Konishi <[email protected]>
Subject: nilfs2: fix potential UAF of struct nilfs_sc_info in nilfs_segctor_thread()
Date: Tue, 28 Mar 2023 02:53:18 +0900

The finalization of nilfs_segctor_thread() can race with nilfs_segctor_kill_thread() which terminates that thread, potentially causing a use-after-free BUG as KASAN detected.

At the end of nilfs_segctor_thread(), it assigns NULL to "sc_task" member of "struct nilfs_sc_info" to indicate the thread has finished, and then notifies nilfs_segctor_kill_thread() of this using waitqueue "sc_wait_task" on the struct nilfs_sc_info.

However, here, immediately after the NULL assignment to "sc_task", it is possible that nilfs_segctor_kill_thread() will detect it and return to continue the deallocation, freeing the nilfs_sc_info structure before the thread does the notification.

This fixes the issue by protecting the NULL assignment to "sc_task" and its notification, with spinlock "sc_state_lock" of the struct nilfs_sc_info. Since nilfs_segctor_kill_thread() does a final check to see if "sc_task" is NULL with "sc_state_lock" locked, this can eliminate the race.

---

 fs/nilfs2/segment.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

@@ -2609,11 +2609,10 @@ static int nilfs_segctor_thread(void *ar
 	goto loop;
 
  end_thread:
-	spin_unlock(&sci->sc_state_lock);
-
 	/* end sync. */
 	sci->sc_task = NULL;
 	wake_up(&sci->sc_wait_task); /* for nilfs_segctor_kill_thread() */
+	spin_unlock(&sci->sc_state_lock);
 	return 0;
 }
 

_

Patches currently in -mm which might be from [email protected] are