Re: sound: use-after-free in snd_timer_stop
From: Dmitry Vyukov
Date: Tue Jan 12 2016 - 11:46:42 EST
On Tue, Jan 12, 2016 at 3:16 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Tue, 12 Jan 2016 15:05:24 +0100,
> Takashi Iwai wrote:
>> On Tue, 12 Jan 2016 11:22:09 +0100,
>> Dmitry Vyukov wrote:
>> > Hello,
>> > I've hit the following use-after-free while running syzkaller fuzzer.
>> > It is followed by a splat of other reports and finally kernel death.
>> > I wasn't able to reproduce it with a standalone C program (there is
>> > probably some global state involved). But it reproduces by replaying
>> > fuzzer logs in a loop (you will need Go toolchain):
>> > $ go get github.com/google/syzkaller
>> > $ cd $GOPATH/src/github.com/google/syzkaller
>> > $ make executor execprog
>> Just a note: I had to run "mkdir bin" beforehand.
>> Also for my distro, I had to remove -static.
>> > $ scp bin/syz-executor bin/syz-execprog your@machine
>> > $ scp snd_timer_stop your@machine # the attached file
>> > on test machine:
>> > $ ./syz-execprog -executor ./syz-executor -cover=0 -repeat=0 -procs=16
>> > snd_timer_stop
>> I tried this but couldn't reproduce the issue on my machine,
>> unfortunately. (Instead I hit another kernel panic regarding apparmor
>> But looking through your log, it seems like a missing race
>> protection. Does the patch below work for you?
> Gah, scratch this. The second hunk causes a deadlock.
> The revised patch is below (just containing the first hunk).
Yes, this patch fixes the crashes for me.
Reproduction may require running syz-execprog for several minutes.
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c
> index 7dfd0f429410..0bec02e89d51 100644
> --- a/sound/core/seq/seq_queue.c
> +++ b/sound/core/seq/seq_queue.c
> @@ -142,8 +142,10 @@ static struct snd_seq_queue *queue_new(int owner, int locked)
> static void queue_delete(struct snd_seq_queue *q)
> /* stop and release the timer */
> + mutex_lock(&q->timer_mutex);
> + mutex_unlock(&q->timer_mutex);
> /* wait until access free */
> /* release resources... */