[syzbot] UBSAN: shift-out-of-bounds in snd_timer_user_ccallback

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5ff2756a Merge tag 'nfs-for-5.13-2' of git://git.linux-nfs..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17872d5bd00000
kernel config: https://syzkaller.appspot.com/x/.config?x=770708ea7cfd4916
dashboard link: https://syzkaller.appspot.com/bug?extid=d102fa5b35335a7e544e

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d102fa...@syzkaller.appspotmail.com

================================================================================
UBSAN: shift-out-of-bounds in sound/core/timer.c:1376:23
shift exponent 105 is too large for 32-bit type 'int'
CPU: 1 PID: 10368 Comm: syz-executor.1 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
__ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:327
snd_timer_user_ccallback.cold+0x19/0x1e sound/core/timer.c:1376
snd_timer_notify1+0x243/0x3b0 sound/core/timer.c:525
snd_timer_stop1+0x641/0x890 sound/core/timer.c:656
snd_timer_pause+0x6e/0x90 sound/core/timer.c:738
seq_timer_stop sound/core/seq/seq_timer.c:331 [inline]
snd_seq_timer_stop+0x93/0xd0 sound/core/seq/seq_timer.c:341
queue_delete+0x42/0xa0 sound/core/seq/seq_queue.c:133
snd_seq_queue_client_leave+0x37/0x1a0 sound/core/seq/seq_queue.c:552
seq_free_client1.part.0+0x10a/0x260 sound/core/seq/seq_clientmgr.c:280
seq_free_client1 sound/core/seq/seq_clientmgr.c:273 [inline]
seq_free_client+0x7b/0xf0 sound/core/seq/seq_clientmgr.c:301
snd_seq_release+0x4d/0xe0 sound/core/seq/seq_clientmgr.c:382
__fput+0x288/0x920 fs/file_table.c:280
task_work_run+0xdd/0x1a0 kernel/task_work.c:164
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
exit_to_user_mode_prepare+0x272/0x280 kernel/entry/common.c:208
__syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:301
do_syscall_64+0x47/0xb0 arch/x86/entry/common.c:57
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4193eb
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:0000000000a9fb80 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 00000000004193eb
RDX: 0000000000571b58 RSI: ffffffff89166efe RDI: 0000000000000004
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000001b2ea280a8
R10: 00000000000001d1 R11: 0000000000000293 R12: 000000000014d248
R13: 00000000000003e8 R14: 000000000056bf80 R15: 000000000014d1dd
================================================================================


---
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[Dongliang Mu]

On Wednesday, June 2, 2021 at 7:58:22 AM UTC+8 syzbot wrote:

Hello,

syzbot found the following issue on:

HEAD commit: 5ff2756a Merge tag 'nfs-for-5.13-2' of git://git.linux-nfs..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17872d5bd00000
kernel config: https://syzkaller.appspot.com/x/.config?x=770708ea7cfd4916
dashboard link: https://syzkaller.appspot.com/bug?extid=d102fa5b35335a7e544e

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d102fa...@syzkaller.appspotmail.com

================================================================================
UBSAN: shift-out-of-bounds in sound/core/timer.c:1376:23
shift exponent 105 is too large for 32-bit type 'int'
CPU: 1 PID: 10368 Comm: syz-executor.1 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
__ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:327
snd_timer_user_ccallback.cold+0x19/0x1e sound/core/timer.c:1376

snd_timer_notify1+0x243/0x3b0 sound/core/timer.c:525

The root cause of this bug is in the snd_timer_notify1 [1]. At the end of this function, it calls "ts->ccallback(ts, event + 100, &tstamp, resolution)".

Here the variable event is 5. It adds 100 and is passed as 2nd argument of snd_timer_user_ccallback.

From the variable naming, the 2nd argument should an event, and in the range of event enumeration. In fact, 105(event + 100) is out of this range. I don't quite understand the meaning of adding 100. Any thought here?

BTW, before I understand the question above, I proposed the following patch:

diff --git a/sound/core/timer.c b/sound/core/timer.c

index 6898b1ac0d7f..e27ce62428e8 100644

--- a/sound/core/timer.c

+++ b/sound/core/timer.c

@@ -1370,6 +1370,9 @@ static void snd_timer_user_ccallback(struct snd_timer_instance *timeri,

        struct snd_timer_tread64 r1;

        unsigned long flags;

 

+       if (snd_BUG_ON(event < SNDRV_TIMER_EVENT_START ||

+                      event > SNDRV_TIMER_EVENT_PAUSE))

+               return;

        if (event >= SNDRV_TIMER_EVENT_START &&

            event <= SNDRV_TIMER_EVENT_PAUSE)

                tu->tstamp = *tstamp;

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/core/timer.c?id=5ff2756afde08b266fbb673849899fec694f39f1#n497

[Dongliang Mu]

range of event enumeration. In fact, 105 (event + 100) is out of this

range. I don't quite understand the meaning of adding 100. Any thought
here?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/core/timer.c?id=5ff2756afde08b266fbb673849899fec694f39f1#n497

--
My best regards to you.

No System Is Safe!
Dongliang Mu

[Jaroslav Kysela]

It seems that the original intent was to move the event to the M... events:

SNDRV_TIMER_EVENT_MSTART = SNDRV_TIMER_EVENT_START + 10,

So the added value should be 10 which should not break the shift range (8
/resume/ + 10 = 18).

Jaroslav

>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/core/timer.c?id=5ff2756afde08b266fbb673849899fec694f39f1#n497
>
> --
> My best regards to you.
>
> No System Is Safe!
> Dongliang Mu
>

--
Jaroslav Kysela <pe...@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

[Dongliang Mu]

It seems you are right. Then event should be between
SNDRV_TIMER_EVENT_MSTART and SNDRV_TIMER_EVENT_MPAUSE.

I double check all the ccallback site, only snd_timer_notify1 invokes
ccallback with event + 100, others seem ok.

1 timer.c snd_timer_notify1 515 if (ti->ccallback)
2 timer.c snd_timer_notify1 516 ti->ccallback(ti, event,
&tstamp, resolution);
3 timer.c snd_timer_notify1 524 if (ts->ccallback)
4 timer.c snd_timer_notify1 525 ts->ccallback(ts, event + 100,
&tstamp, resolution);
5 timer.c snd_timer_notify 1092 if (ti->ccallback)
6 timer.c snd_timer_notify 1093 ti->ccallback(ti, event,
tstamp, resolution);
7 timer.c snd_timer_notify 1095 if (ts->ccallback)
8 timer.c snd_timer_notify 1096 ts->ccallback(ts, event,
tstamp, resolution);
9 timer.c snd_timer_user_tselect 1782 tu->timeri->ccallback =
snd_timer_user_ccallback;
a aloop.c loopback_snd_timer_open 1137 timeri->ccallback =
loopback_snd_timer_event;

[Takashi Iwai]

The bug has been already fixed, but unfortunately my submission didn't go out to ML due to some SMPT server problem.

(So now I'm using a different system, hopefully it goes out somehow, sorry for the top-post due to that...)

I'll resend the patch later, but the fix is found in for-linus branch commit ae352822321d2e8eb17347ab4eb64e461bea6971.

https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/?h=for-linus&id=ae352822321d2e8eb17347ab4eb64e461bea6971

Takashi

---

From: Dongliang Mu <mudongl...@gmail.com>
Sent: Wednesday, June 2, 2021 3:18 PM
To: allen...@gmail.com <allen...@gmail.com>; alsa-...@alsa-project.org <alsa-...@alsa-project.org>; Joe Perches <j...@perches.com>; linux-kernel <linux-...@vger.kernel.org>; pe...@perex.cz <pe...@perex.cz>; pierre-lou...@linux.intel.com <pierre-lou...@linux.intel.com>; romain...@gmail.com <romain...@gmail.com>; syzkaller-bugs <syzkall...@googlegroups.com>; Takashi Iwai <ti...@suse.com>
Subject: [syzbot] UBSAN: shift-out-of-bounds in snd_timer_user_ccallback

 

[Takashi Iwai]

I've already submitted the fix patch, but it doesn't seem reaching
properly to ML. Hmm. Will resend.


Takashi