The patch titled Subject: nilfs2: fix potential UAF of struct nilfs_sc_info in nilfs_segctor_thread() has been added to the -mm mm-hotfixes-unstable branch. Its filename is nilfs2-fix-potential-uaf-of-struct-nilfs_sc_info-in-nilfs_segctor_thread.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryusuke Konishi konishi.ryusuke@gmail.com 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.

Link: https://lkml.kernel.org/r/20230327175318.8060-1-konishi.ryusuke@gmail.com Reported-by: syzbot+b08ebcc22f8f3e6be43a@syzkaller.appspotmail.com Link: https://lkml.kernel.org/r/00000000000000660d05f7dfa877@google.com Signed-off-by: Ryusuke Konishi konishi.ryusuke@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/fs/nilfs2/segment.c~nilfs2-fix-potential-uaf-of-struct-nilfs_sc_info-in-nilfs_segctor_thread +++ a/fs/nilfs2/segment.c @@ -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; }

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Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-fix-potential-uaf-of-struct-nilfs_sc_info-in-nilfs_segctor_thread.patch