sound: use-after-free in hrtimer_cancel

[Dmitry Vyukov]

Hello,

The following program triggers use-after-free:

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <pthread.h>
#include <stdint.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>

long r[20];

void* thr(void* arg)
{
switch ((long)arg) {
case 0:
break;
case 1:
r[2] = syscall(SYS_open, "/dev/audio", 0xa40ul, 0, 0, 0);
break;
case 2:
*(uint32_t*)0x2001dde8 = r[2];
*(uint16_t*)0x2001ddec = (uint16_t)0x0;
*(uint16_t*)0x2001ddee = (uint16_t)0x2;
*(uint32_t*)0x2001ddf0 = r[2];
*(uint16_t*)0x2001ddf4 = (uint16_t)0xfffffffff3a15aea;
*(uint16_t*)0x2001ddf6 = (uint16_t)0x1;
*(uint32_t*)0x2001ddf8 = r[2];
*(uint16_t*)0x2001ddfc = (uint16_t)0x836a;
*(uint16_t*)0x2001ddfe = (uint16_t)0x1ff;
*(uint32_t*)0x2001de00 = r[2];
*(uint16_t*)0x2001de04 = (uint16_t)0x0;
*(uint16_t*)0x2001de06 = (uint16_t)0x20;
r[15] = syscall(SYS_poll, 0x2001dde8ul, 0x4ul, 0x8ul, 0, 0, 0);
break;
case 3:
*(uint64_t*)0x20dc13c0 = (uint64_t)0x20dc1f27;
*(uint64_t*)0x20dc13c8 = (uint64_t)0xd9;
r[18] = syscall(SYS_readv, r[2], 0x20dc13c0ul, 0x1ul, 0, 0, 0);
break;
case 4:
r[19] = syscall(SYS_read, r[2], 0x20dbefe0ul, 0x20ul, 0, 0, 0);
break;
}
return 0;
}

int main()
{
long i;
pthread_t th[10];

syscall(SYS_mmap, 0x20000000ul, 0xde0000ul, 0x3ul, 0x32ul,
0xfffffffffffffffful, 0x0ul);
srand(getpid());
memset(r, -1, sizeof(r));
for (i = 0; i < 5; i++) {
pthread_create(&th[i], 0, thr, (void*)i);
usleep(rand()%5000);
}
for (i = 0; i < 5; i++) {
pthread_create(&th[5+i], 0, thr, (void*)i);
if (rand()%2)
usleep(rand()%5000);
}
for (i = 0; i < 10; i++) {
pthread_join(th[i], 0);
}
return 0;
}


Here are 2 reports (note they are slightly different):

==================================================================
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
cpu=2172593693 pid=-1
[< inline >] kmalloc include/linux/slab.h:478
[< inline >] kzalloc include/linux/slab.h:622
[< none >] dummy_hrtimer_create+0x49/0x1a0 sound/drivers/dummy.c:464
[< none >] ___slab_alloc+0x55d/0x5a0 mm/slub.c:2476
[< none >] __slab_alloc+0x68/0xc0 mm/slub.c:2505
[< inline >] slab_alloc_node mm/slub.c:2568
[< inline >] slab_alloc mm/slub.c:2610
[< none >] kmem_cache_alloc_trace+0x263/0x3d0 mm/slub.c:2627
[< inline >] kmalloc include/linux/slab.h:478
[< inline >] kzalloc include/linux/slab.h:622
[< none >] dummy_hrtimer_create+0x49/0x1a0 sound/drivers/dummy.c:464
[< none >] dummy_pcm_open+0xcd/0x5e0 sound/drivers/dummy.c:574
[< none >] snd_pcm_open_substream+0x188/0x430
sound/core/pcm_native.c:2276
[< inline >] snd_pcm_oss_open_file sound/core/oss/pcm_oss.c:2346
[< none >] snd_pcm_oss_open.part.17+0x5a4/0x1110
sound/core/oss/pcm_oss.c:2428
[< none >] snd_pcm_oss_open+0x35/0x50 sound/core/oss/pcm_oss.c:2392
[< none >] soundcore_open+0x30f/0x640 sound/sound_core.c:639
[< none >] chrdev_open+0x22a/0x4c0 fs/char_dev.c:388
[< none >] do_dentry_open+0x6a2/0xcb0 fs/open.c:736
[< none >] vfs_open+0x17b/0x1f0 fs/open.c:853
[< inline >] do_last fs/namei.c:3238
[< none >] path_openat+0x51bb/0x5ce0 fs/namei.c:3374
[< none >] do_filp_open+0x18e/0x250 fs/namei.c:3409
[< none >] do_sys_open+0x1fc/0x420 fs/open.c:1020

INFO: Freed in 0xfffd8e09 age=18446705496313138713 cpu=2164287125 pid=-1
[< none >] dummy_hrtimer_free+0x68/0x80 sound/drivers/dummy.c:481
[< none >] __slab_free+0x1e8/0x300 mm/slub.c:2687
[< inline >] slab_free mm/slub.c:2840
[< none >] kfree+0x2fc/0x370 mm/slub.c:3691
[< none >] dummy_hrtimer_free+0x68/0x80 sound/drivers/dummy.c:481
[< none >] dummy_pcm_close+0x9c/0xd0 sound/drivers/dummy.c:607
[< none >] snd_pcm_release_substream.part.37+0x169/0x2f0
sound/core/pcm_native.c:2241
[< none >] snd_pcm_release_substream+0x59/0x70
sound/core/pcm_native.c:2251
[< none >] snd_pcm_oss_release_file+0x7b/0xb0
sound/core/oss/pcm_oss.c:2305
[< none >] snd_pcm_oss_release+0xfa/0x280
sound/core/oss/pcm_oss.c:2485
[< none >] __fput+0x236/0x780 fs/file_table.c:208
[< none >] ____fput+0x15/0x20 fs/file_table.c:244
[< none >] task_work_run+0x170/0x210 kernel/task_work.c:115
[< inline >] exit_task_work include/linux/task_work.h:21
[< none >] do_exit+0x874/0x2d80 kernel/exit.c:748
[< none >] do_group_exit+0x108/0x330 kernel/exit.c:878
[< none >] get_signal+0x634/0x15e0 kernel/signal.c:2307
[< none >] do_signal+0x7f/0x1cf0 arch/x86/kernel/signal.c:784

INFO: Indirect in 0xfffd8e17 age=4294807066 cpu=0 pid=0
INFO: Slab 0xffffea0001796d00 objects=24 used=15 fp=0xffff88005e5b71e8
flags=0x4fffe0000004080
INFO: Object 0xffff88005e5b6f40 @offset=12096 fp=0xbbbbbbbbbbbbbbbb
CPU: 1 PID: 8984 Comm: syz-executor Tainted: G B 4.6.0-rc6+ #355
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
ffffffff87eb25c0 ffff880059fd7378 ffffffff82c9062f ffffffff5e5b4000
fffffbfff0fd64b8 ffff88003e804d40 ffff88005e5b6f40 ffffea0001796d00
ffff88005e5b4000 0000000000000000 ffff880059fd73a8 ffffffff81793e1d

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
[<ffffffff817fc066>] __fput+0x236/0x780 fs/file_table.c:208
[<ffffffff817fc635>] ____fput+0x15/0x20 fs/file_table.c:244
[<ffffffff813c91d0>] task_work_run+0x170/0x210 kernel/task_work.c:115
[< inline >] exit_task_work include/linux/task_work.h:21
[<ffffffff81373e64>] do_exit+0x874/0x2d80 kernel/exit.c:748
[<ffffffff813764e8>] do_group_exit+0x108/0x330 kernel/exit.c:878
[<ffffffff81399674>] get_signal+0x634/0x15e0 kernel/signal.c:2307
[<ffffffff811f40af>] do_signal+0x7f/0x1cf0 arch/x86/kernel/signal.c:784
[<ffffffff81006695>] exit_to_usermode_loop+0x1a5/0x210
arch/x86/entry/common.c:229
[< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:264
[<ffffffff8100868f>] syscall_return_slowpath+0x2bf/0x340
arch/x86/entry/common.c:329
[<ffffffff867c56dc>] entry_SYSCALL_64_fastpath+0xbf/0xc1
arch/x86/entry/entry_64.S:241
==================================================================





==================================================================
BUG: KASAN: use-after-free in timerqueue_add+0x29a/0x2a0 at addr
ffff880062134580
Read of size 8 by task a.out/12711
=============================================================================
BUG kmalloc-192 (Not tainted): kasan: bad access detected
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: Allocated in 0xbbbbbbbbbbbbbbbb age=18446689703718641197
cpu=2172593693 pid=-1
[< inline >] kmalloc include/linux/slab.h:478
[< inline >] kzalloc include/linux/slab.h:622
[< none >] dummy_hrtimer_create+0x49/0x1a0 sound/drivers/dummy.c:464
[< none >] ___slab_alloc+0x55d/0x5a0 mm/slub.c:2476
[< none >] __slab_alloc+0x68/0xc0 mm/slub.c:2505
[< inline >] slab_alloc_node mm/slub.c:2568
[< inline >] slab_alloc mm/slub.c:2610
[< none >] kmem_cache_alloc_trace+0x263/0x3d0 mm/slub.c:2627
[< inline >] kmalloc include/linux/slab.h:478
[< inline >] kzalloc include/linux/slab.h:622
[< none >] dummy_hrtimer_create+0x49/0x1a0 sound/drivers/dummy.c:464
[< none >] dummy_pcm_open+0xcd/0x5e0 sound/drivers/dummy.c:574
[< none >] snd_pcm_open_substream+0x188/0x430
sound/core/pcm_native.c:2276
[< inline >] snd_pcm_oss_open_file sound/core/oss/pcm_oss.c:2346
[< none >] snd_pcm_oss_open.part.17+0x5a4/0x1110
sound/core/oss/pcm_oss.c:2428
[< none >] snd_pcm_oss_open+0x35/0x50 sound/core/oss/pcm_oss.c:2392
[< none >] soundcore_open+0x30f/0x640 sound/sound_core.c:639
[< none >] chrdev_open+0x22a/0x4c0 fs/char_dev.c:388
[< none >] do_dentry_open+0x6a2/0xcb0 fs/open.c:736
[< none >] vfs_open+0x17b/0x1f0 fs/open.c:853
[< inline >] do_last fs/namei.c:3238
[< none >] path_openat+0x51bb/0x5ce0 fs/namei.c:3374
[< none >] do_filp_open+0x18e/0x250 fs/namei.c:3409
[< none >] do_sys_open+0x1fc/0x420 fs/open.c:1020

INFO: Freed in 0x100015e1b age=18446689836862627373 cpu=0 pid=0
[< none >] dummy_hrtimer_free+0x68/0x80 sound/drivers/dummy.c:481
[< none >] __slab_free+0x1e8/0x300 mm/slub.c:2687
[< inline >] slab_free mm/slub.c:2840
[< none >] kfree+0x2fc/0x370 mm/slub.c:3691
[< none >] dummy_hrtimer_free+0x68/0x80 sound/drivers/dummy.c:481
[< none >] dummy_pcm_close+0x9c/0xd0 sound/drivers/dummy.c:607
[< none >] snd_pcm_release_substream.part.37+0x169/0x2f0
sound/core/pcm_native.c:2241
[< none >] snd_pcm_release_substream+0x59/0x70
sound/core/pcm_native.c:2251
[< none >] snd_pcm_oss_release_file+0x7b/0xb0
sound/core/oss/pcm_oss.c:2305
[< none >] snd_pcm_oss_release+0xfa/0x280
sound/core/oss/pcm_oss.c:2485
[< none >] __fput+0x236/0x780 fs/file_table.c:208
[< none >] ____fput+0x15/0x20 fs/file_table.c:244
[< none >] task_work_run+0x170/0x210 kernel/task_work.c:115
[< inline >] exit_task_work include/linux/task_work.h:21
[< none >] do_exit+0x874/0x2d80 kernel/exit.c:748
[< none >] do_group_exit+0x108/0x330 kernel/exit.c:878
[< inline >] SYSC_exit_group kernel/exit.c:889
[< none >] SyS_exit_group+0x1d/0x20 kernel/exit.c:887
[< none >] entry_SYSCALL_64_fastpath+0x23/0xc1
arch/x86/entry/entry_64.S:207

INFO: Indirect in 0x100015e2e age=4295056943 cpu=0 pid=0
INFO: Slab 0xffffea0001884d00 objects=24 used=10 fp=0xffff880062135a48
flags=0x4fffe0000004080
INFO: Object 0xffff880062134540 @offset=1344 fp=0xbbbbbbbbbbbbbbbb
CPU: 2 PID: 12711 Comm: a.out Tainted: G B 4.6.0-rc6+ #355
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
ffffffff87eb25c0 ffff88006d407c60 ffffffff82c9062f ffffffff62134000
fffffbfff0fd64b8 ffff88003e804d40 ffff880062134540 ffffea0001884d00
ffff880062134000 ffff88006d417f10 ffff88006d407c90 ffffffff81793e1d

Call Trace:
[<ffffffff8179e59e>] __asan_report_load8_noabort+0x3e/0x40
mm/kasan/report.c:333
[<ffffffff82cb022a>] timerqueue_add+0x29a/0x2a0 lib/timerqueue.c:51
[<ffffffff814d1066>] enqueue_hrtimer+0x116/0x3d0 kernel/time/hrtimer.c:879
[< inline >] __run_hrtimer kernel/time/hrtimer.c:1257
[<ffffffff814d1c5e>] __hrtimer_run_queues+0x93e/0xe90
kernel/time/hrtimer.c:1306
[<ffffffff814d4022>] hrtimer_interrupt+0x182/0x430 kernel/time/hrtimer.c:1340
[<ffffffff8125aa62>] local_apic_timer_interrupt+0x72/0xe0
arch/x86/kernel/apic/apic.c:907
[<ffffffff867c7f59>] smp_apic_timer_interrupt+0x79/0xa0
arch/x86/kernel/apic/apic.c:931
[<ffffffff867c62ac>] apic_timer_interrupt+0x8c/0xa0
arch/x86/entry/entry_64.S:454
[<ffffffff813c93d3>] __kernel_text_address+0x73/0xa0 kernel/extable.c:103
[<ffffffff811fd73e>] print_context_stack+0x6e/0xc0
arch/x86/kernel/dumpstack.c:107
[<ffffffff811fc984>] dump_trace+0x124/0x320 arch/x86/kernel/dumpstack_64.c:243
[<ffffffff8121d396>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:67
[< inline >] __save_stack_trace mm/kmemleak.c:530
[<ffffffff817e2467>] create_object+0x137/0x2d0 mm/kmemleak.c:585
[<ffffffff867a7d43>] kmemleak_alloc+0x63/0xa0 mm/kmemleak.c:915
[< inline >] kmemleak_alloc_recursive include/linux/kmemleak.h:47
[< inline >] slab_post_alloc_hook mm/slab.h:406
[< inline >] slab_alloc_node mm/slub.c:2602
[< inline >] slab_alloc mm/slub.c:2610
[<ffffffff81798236>] kmem_cache_alloc+0x166/0x3c0 mm/slub.c:2615
[<ffffffff81727df0>] ptlock_alloc+0x20/0x80 mm/memory.c:3968
[< inline >] ptlock_init include/linux/mm.h:1625
[< inline >] pgtable_page_ctor include/linux/mm.h:1659
[<ffffffff81299ba9>] pte_alloc_one+0x59/0x100 arch/x86/mm/pgtable.c:31
[<ffffffff81716c68>] __pte_alloc+0x28/0x2a0 mm/memory.c:569
[< inline >] __handle_mm_fault mm/memory.c:3470
[<ffffffff81721a6a>] handle_mm_fault+0xc0a/0x11a0 mm/memory.c:3522
[<ffffffff8128ad47>] __do_page_fault+0x457/0xbb0 arch/x86/mm/fault.c:1351
[<ffffffff8128b5ef>] trace_do_page_fault+0xdf/0x5b0 arch/x86/mm/fault.c:1444
[<ffffffff8127bd84>] do_async_page_fault+0x14/0xd0 arch/x86/kernel/kvm.c:265
[<ffffffff867c77f8>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:920
==================================================================


On commit 83858a701cf3271f81dd321c2a81e5666c6ca8f4 (note it is not
super fresh: May 3).

[Dmitry Vyukov]

On Sat, Jun 4, 2016 at 8:00 PM, Dmitry Vyukov <dvy...@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.

[Takashi Iwai]

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);
}

[Dmitry Vyukov]

On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <ti...@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 <dvy...@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?

I use a VM with 4 cores and use 20 parallel test processes.

> 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?

I think poll with timeout is related. It is poll who sets hrtimer, right?

> Also, this assumes that the first sound card is Dummy driver, right?
> Check /proc/asound/cards.

# cat /proc/asound/cards
0 [Dummy ]: Dummy - Dummy
Dummy 1
1 [Loopback ]: Loopback - Loopback
Loopback 1
2 [VirMIDI ]: VirMIDI - VirMIDI
Virtual MIDI Card 1
3 [pcsp ]: PC-Speaker - pcsp
Internal PC-Speaker at port 0x61
4 [Intel ]: HDA-Intel - HDA Intel
HDA Intel at 0xfebf0000 irq 24

[Takashi Iwai]

On Mon, 06 Jun 2016 18:29:25 +0200,

Dmitry Vyukov wrote:
>
> On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <ti...@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 <dvy...@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?
>
> I use a VM with 4 cores and use 20 parallel test processes.
>
> > 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?
>
>
> I think poll with timeout is related. It is poll who sets hrtimer, right?

If it's about snd-dummy driver, hrtimer is created at open, and
started/stopped at PCM trigger, and removed at close.

Is there any good way to decode which syscalls are executed in the
test code?


Takashi

[Jeremy Huang]

Hi,

it's like the CVE-2016-2549.

which kernel version did you fuzz?

Jeremy

Dmitry Vyukov於 2016年6月5日星期日 UTC+8上午2時00分26秒寫道：

[Dmitry Vyukov]

On Tue, Jun 7, 2016 at 7:25 AM, Jeremy Huang <jere...@gmail.com> wrote:
> Hi,
>
> it's like the CVE-2016-2549.
> which kernel version did you fuzz?

Why do you that this is like exactly CVE-2016-2549? I've found 28 bugs in sound:
https://github.com/google/syzkaller/wiki/Found-Bugs
Lots of them look similar at first sight.

Fix for that particular bug was submitted long time ago:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2ba1fe7a06d3624f9a7586d672b55f08f7c670f3

I've provided commit I am testing at in the original message:
83858a701cf3271f81dd321c2a81e5666c6ca8f4. It should include the fix.

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[Dmitry Vyukov]

On Mon, Jun 6, 2016 at 6:39 PM, Takashi Iwai <ti...@suse.de> wrote:
> On Mon, 06 Jun 2016 18:29:25 +0200,
> Dmitry Vyukov wrote:
>>
>> On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <ti...@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 <dvy...@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?
>>
>> I use a VM with 4 cores and use 20 parallel test processes.
>>
>> > 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?
>>
>>
>> I think poll with timeout is related. It is poll who sets hrtimer, right?
>
> If it's about snd-dummy driver, hrtimer is created at open, and
> started/stopped at PCM trigger, and removed at close.
>
> Is there any good way to decode which syscalls are executed in the
> test code?

What do you mean?
Here are the syscalls in the program:

r[2] = syscall(SYS_open, "/dev/audio", 0xa40ul, 0, 0, 0);

// r[2] is in the descriptor passed to SYS_poll

r[15] = syscall(SYS_poll, 0x2001dde8ul, 0x4ul, 0x8ul, 0, 0, 0);

r[18] = syscall(SYS_readv, r[2], 0x20dc13c0ul, 0x1ul, 0, 0, 0);

[Dmitry Vyukov]

On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <ti...@suse.de> wrote:

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.
Please mail a patch.

[Takashi Iwai]

On Tue, 21 Jun 2016 20:26:48 +0200,

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 <ti...@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 <dvy...@google.com>
Signed-off-by: Takashi Iwai <ti...@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);
}

--
2.9.0

[Takashi Iwai]

On Tue, 21 Jun 2016 19:41:28 +0200,

I meant some nice way to decode these magic numbers to be more
understandable :)


Takashi

[Dmitry Vyukov]

Sure.

Tested-by: Dmitry Vyukov <dvy...@google.com>

[Dmitry Vyukov]

Short term, run it under strace. It should show file names, decode
most of flags and structs.

[Takashi Iwai]

On Fri, 24 Jun 2016 15:48:53 +0200,

Alright, thanks.


Takashi

[Takashi Iwai]

On Fri, 24 Jun 2016 15:33:35 +0200,

Thanks, the patch queued with your tags, now.


Takashi