On Tue, 21 Jun 2016 20:26:48 +0200, Dmitry Vyukov wrote:
On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai tiwai@suse.de wrote:
On Sat, 04 Jun 2016 20:27:50 +0200, Dmitry Vyukov wrote:
On Sat, Jun 4, 2016 at 8:00 PM, Dmitry Vyukov dvyukov@google.com wrote:
Hello,
The following program triggers use-after-free:
Forget to mention that you need to run it in a tight parallel loop. It takes around 5 minutes to reproduce for me.
Hmm, this again is a bug that is difficult to trigger... At least, I couldn't reproduce locally. How many processes are you running with stress program?
It seems that there is nothing more than opening /dev/audio and does some mmap in the job. Is there any other relevant thing there?
Also, this assumes that the first sound card is Dummy driver, right? Check /proc/asound/cards.
If it's about snd-dummy driver, one blind shot would be a patch like below. But even if it would fix, it doesn't explain why it's triggered in that way...
thanks,
Takashi
diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c index c0f8f613f1f1..172dacd925f5 100644 --- a/sound/drivers/dummy.c +++ b/sound/drivers/dummy.c @@ -420,6 +420,7 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream)
static inline void dummy_hrtimer_sync(struct dummy_hrtimer_pcm *dpcm) {
hrtimer_cancel(&dpcm->timer); tasklet_kill(&dpcm->tasklet);}
Yes, this seems to fix it. I've stressed it for an hour with several reproducers. If I am not mistaken, it also makes test cases run 15% faster.
Interesting. Possibly because it now syncs properly before other restart of stream or such...
Please mail a patch.
OK, below is the formal patch. Let me know if I can give your tested-by tag.
thanks,
Takashi
-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: dummy: Fix a use-after-free at closing
syzkaller fuzzer spotted a potential use-after-free case in snd-dummy driver when hrtimer is used as backend:
================================================================== BUG: KASAN: use-after-free in rb_erase+0x1b17/0x2010 at addr ffff88005e5b6f68 Read of size 8 by task syz-executor/8984 ============================================================================= BUG kmalloc-192 (Not tainted): kasan: bad access detected
Disabling lock debugging due to kernel taint INFO: Allocated in 0xbbbbbbbbbbbbbbbb age=18446705582212484632 .... [< none >] dummy_hrtimer_create+0x49/0x1a0 sound/drivers/dummy.c:464 .... INFO: Freed in 0xfffd8e09 age=18446705496313138713 cpu=2164287125 pid=-1 [< none >] dummy_hrtimer_free+0x68/0x80 sound/drivers/dummy.c:481 .... Call Trace: [<ffffffff8179e59e>] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:333 [< inline >] rb_set_parent include/linux/rbtree_augmented.h:111 [< inline >] __rb_erase_augmented include/linux/rbtree_augmented.h:218 [<ffffffff82ca5787>] rb_erase+0x1b17/0x2010 lib/rbtree.c:427 [<ffffffff82cb02e8>] timerqueue_del+0x78/0x170 lib/timerqueue.c:86 [<ffffffff814d0c80>] __remove_hrtimer+0x90/0x220 kernel/time/hrtimer.c:903 [< inline >] remove_hrtimer kernel/time/hrtimer.c:945 [<ffffffff814d23da>] hrtimer_try_to_cancel+0x22a/0x570 kernel/time/hrtimer.c:1046 [<ffffffff814d2742>] hrtimer_cancel+0x22/0x40 kernel/time/hrtimer.c:1066 [<ffffffff85420531>] dummy_hrtimer_stop+0x91/0xb0 sound/drivers/dummy.c:417 [<ffffffff854228bf>] dummy_pcm_trigger+0x17f/0x1e0 sound/drivers/dummy.c:507 [<ffffffff85392170>] snd_pcm_do_stop+0x160/0x1b0 sound/core/pcm_native.c:1106 [<ffffffff85391b26>] snd_pcm_action_single+0x76/0x120 sound/core/pcm_native.c:956 [<ffffffff85391e01>] snd_pcm_action+0x231/0x290 sound/core/pcm_native.c:974 [< inline >] snd_pcm_stop sound/core/pcm_native.c:1139 [<ffffffff8539754d>] snd_pcm_drop+0x12d/0x1d0 sound/core/pcm_native.c:1784 [<ffffffff8539d3be>] snd_pcm_common_ioctl1+0xfae/0x2150 sound/core/pcm_native.c:2805 [<ffffffff8539ee91>] snd_pcm_capture_ioctl1+0x2a1/0x5e0 sound/core/pcm_native.c:2976 [<ffffffff8539f2ec>] snd_pcm_kernel_ioctl+0x11c/0x160 sound/core/pcm_native.c:3020 [<ffffffff853d9a44>] snd_pcm_oss_sync+0x3a4/0xa30 sound/core/oss/pcm_oss.c:1693 [<ffffffff853da27d>] snd_pcm_oss_release+0x1ad/0x280 sound/core/oss/pcm_oss.c:2483 .....
A workaround is to call hrtimer_cancel() in dummy_hrtimer_sync() which is called certainly before other blocking ops.
Reported-by: Dmitry Vyukov dvyukov@google.com Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/drivers/dummy.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c index c0f8f613f1f1..172dacd925f5 100644 --- a/sound/drivers/dummy.c +++ b/sound/drivers/dummy.c @@ -420,6 +420,7 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream)
static inline void dummy_hrtimer_sync(struct dummy_hrtimer_pcm *dpcm) { + hrtimer_cancel(&dpcm->timer); tasklet_kill(&dpcm->tasklet); }