loop: add sync_blockdev() in __loop_clr_fd() to prevent UAF#865
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The syzbot report describes a NULL pointer dereference in lo_rw_aio() caused by a race between lo_release() and loop_queue_rq(). __loop_clr_fd() clears lo->lo_backing_file while an already-scheduled asynchronous I/O work (lo_rw_aio) is about to execute on a kworker. Since the kworker enters lo_rw_aio() after lo->lo_backing_file has been set to NULL, it dereferences the NULL pointer when initializing the kiocb, leading to a general protection fault. Fix this by adding sync_blockdev() in __loop_clr_fd() to flush all pending writeback I/O before clearing lo->lo_backing_file. Since the loop disk is already closed at this point, no new I/O can be submitted — only writeback remains. Reported-by: syzbot+cd8a9a308e879a4e2c28@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=cd8a9a308e879a4e2c28 Reported-by: syzbot+bc273027d5643e48e5b3@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=bc273027d5643e48e5b3 Analyzed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Hongling Zeng <zenghongling@kylinos.cn> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Bart Van Assche <bvanassche@acm.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: https://lore.kernel.org/linux-block/9b2032d6-3f36-4d2b-8128-985c08a4fa37@I-love.SAKURA.ne.jp/ Signed-off-by: Ming Lei <tom.leiming@gmail.com>
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Pull request for series with
subject: loop: add sync_blockdev() in __loop_clr_fd() to prevent UAF
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1099111