WARNING in initialize_timer

[syzbot]

Hello,

syzkaller hit the following crash on
43570f0383d6d5879ae585e6c3cf027ba321546f
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.

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


binder: 4519:4521 ioctl 40046205 2 returned -22
binder: 4519:4521 ioctl c0106403 20008ff0 returned -22
WARNING: CPU: 0 PID: 4528 at sound/core/seq/seq_timer.c:358
initialize_timer+0x22d/0x290 sound/core/seq/seq_timer.c:358
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 4528 Comm: syz-executor7 Not tainted 4.15.0-rc1+ #199
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:53
panic+0x1e4/0x41c kernel/panic.c:183
__warn+0x1dc/0x200 kernel/panic.c:547
report_bug+0x211/0x2d0 lib/bug.c:184
fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:177
fixup_bug arch/x86/kernel/traps.c:246 [inline]
do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:295
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:930
RIP: 0010:initialize_timer+0x22d/0x290 sound/core/seq/seq_timer.c:358
RSP: 0018:ffff8801c7dbf880 EFLAGS: 00010012
RAX: 0000000000010000 RBX: ffff8801cdb75800 RCX: ffffffff840e956d
RDX: 00000000000006b6 RSI: ffffc90001f35000 RDI: ffff8801cdb75850
RBP: ffff8801c7dbf8a8 R08: ffffffff86445678 R09: 1ffff10038fb7eb9
R10: ffff8801c97be2c0 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000286 R14: ffff8801cdb75850 R15: ffff8801d92ecb40
seq_timer_start sound/core/seq/seq_timer.c:391 [inline]
snd_seq_timer_start+0x147/0x2b0 sound/core/seq/seq_timer.c:405
snd_seq_queue_process_event sound/core/seq/seq_queue.c:698 [inline]
snd_seq_control_queue+0x2b9/0x640 sound/core/seq/seq_queue.c:759
event_input_timer+0x25/0x30 sound/core/seq/seq_system.c:118
snd_seq_deliver_single_event.constprop.11+0x2fb/0x940
sound/core/seq/seq_clientmgr.c:621
snd_seq_deliver_event+0x176/0x840 sound/core/seq/seq_clientmgr.c:822
snd_seq_client_enqueue_event+0x2b6/0x420 sound/core/seq/seq_clientmgr.c:940
snd_seq_write+0x34d/0x720 sound/core/seq/seq_clientmgr.c:1069
__vfs_write+0xef/0x970 fs/read_write.c:480
vfs_write+0x18f/0x510 fs/read_write.c:544
SYSC_write fs/read_write.c:589 [inline]
SyS_write+0xef/0x220 fs/read_write.c:581
entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x4529d9
RSP: 002b:00007fb9be36ec58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000758248 RCX: 00000000004529d9
RDX: 0000000000000030 RSI: 0000000020e6ffd0 RDI: 000000000000001c
RBP: 00000000000005a2 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f57d0
R13: 00000000ffffffff R14: 00007fb9be36f6d4 R15: 000000000000002a
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Takashi Iwai]

On Thu, 30 Nov 2017 06:59:01 +0100,
syzbot wrote:
>
> Hello,
>
> syzkaller hit the following crash on
> 43570f0383d6d5879ae585e6c3cf027ba321546f
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
>
> Unfortunately, I don't have any reproducer for this bug yet.
>
>
> binder: 4519:4521 ioctl 40046205 2 returned -22
> binder: 4519:4521 ioctl c0106403 20008ff0 returned -22
> WARNING: CPU: 0 PID: 4528 at sound/core/seq/seq_timer.c:358
> initialize_timer+0x22d/0x290 sound/core/seq/seq_timer.c:358

This must be a spurious WARN_ON() when a slave timer is used while the
master is freed.

I'm going to queue the patch below.

#syz fix: ALSA: seq: Remove spurious WARN_ON() at timer check


thanks,

Takashi

-- 8< --
From: Takashi Iwai <ti...@suse.de>
Subject: [PATCH] ALSA: seq: Remove spurious WARN_ON() at timer check

The use of snd_BUG_ON() in ALSA sequencer timer may lead to a spurious
WARN_ON() when a slave timer is deployed as its backend and a
corresponding master timer stops meanwhile. The symptom was triggered
by syzkaller spontaneously.

Since the NULL timer is valid there, rip off snd_BUG_ON().

Reported-by: syzbot <syzk...@googlegroups.com>
Cc: <sta...@vger.kernel.org>
Signed-off-by: Takashi Iwai <ti...@suse.de>
---
sound/core/seq/seq_timer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
index 37d9cfbc29f9..b80985fbc334 100644
--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -355,7 +355,7 @@ static int initialize_timer(struct snd_seq_timer *tmr)
unsigned long freq;

t = tmr->timeri->timer;
- if (snd_BUG_ON(!t))
+ if (!t)
return -EINVAL;

freq = tmr->preferred_resolution;
--
2.15.0