WARNING in snd_interval_mulkdiv

[syzbot]

Hello,

syzkaller hit the following crash on
cf1fb158230edce8a0482bfb2e59b9c390477fb6
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.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


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Reported-by: syzbot+7e6ee5...@syzkaller.appspotmail.com
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audit: type=1400 audit(1515606919.914:7): avc: denied { map } for
pid=3501 comm="syzkaller879499" path="/root/syzkaller879499069" dev="sda1"
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
WARNING: CPU: 1 PID: 3501 at sound/core/pcm_lib.c:563 muldiv32
sound/core/pcm_lib.c:563 [inline]
WARNING: CPU: 1 PID: 3501 at sound/core/pcm_lib.c:563
snd_interval_mulkdiv+0x5a9/0x650 sound/core/pcm_lib.c:756
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 3501 Comm: syzkaller879499 Not tainted 4.15.0-rc7+ #256
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:178
fixup_bug arch/x86/kernel/traps.c:247 [inline]
do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1079
RIP: 0010:muldiv32 sound/core/pcm_lib.c:563 [inline]
RIP: 0010:snd_interval_mulkdiv+0x5a9/0x650 sound/core/pcm_lib.c:756
RSP: 0018:ffff8801c04c7478 EFLAGS: 00010293
RAX: ffff8801c05f43c0 RBX: ffff8801c04c7500 RCX: ffffffff841cb1f9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000f4240
RBP: ffff8801c04c74c0 R08: 000000000000009c R09: ffffed00380bc5e3
R10: 0000000000000013 R11: ffffed00380bc5e2 R12: ffff8801c05e2ec0
R13: ffff8801c05e2eb4 R14: ffff8801c05e2ec8 R15: ffff8801c05e2ebc
snd_pcm_hw_rule_mulkdiv+0xfd/0x1c0 sound/core/pcm_native.c:2040
constrain_params_by_rules+0x625/0x11b0 sound/core/pcm_native.c:400
snd_pcm_hw_refine+0x818/0x1070 sound/core/pcm_native.c:502
snd_pcm_hw_refine_old_user sound/core/pcm_native.c:3612 [inline]
snd_pcm_common_ioctl+0x7f9/0x1f60 sound/core/pcm_native.c:2922
snd_pcm_ioctl+0x81/0xb0 sound/core/pcm_native.c:2959
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x443d79
RSP: 002b:00007ffe547ec708 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000443d79
RDX: 0000000020001f64 RSI: 00000000c1004110 RDI: 0000000000000003
RBP: 00000000006ce018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020005000 R11: 0000000000000286 R12: 0000000000401a60
R13: 0000000000401af0 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[Takashi Iwai]

This is yet another superfluous WARN_ON() to be removed.
I'm going to queue the fix patch below.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <ti...@suse.de>
Subject: [PATCH] ALSA: pcm: Remove yet superfluous WARN_ON()

muldiv32() contains a snd_BUG_ON() (which is morphed as WARN_ON() with
debug option) for checking the case of 0 / 0. This would be helpful
if this happens only as a logical error; however, since the hw refine
is performed with any data set provided by user, the inconsistent
values that can trigger such a condition might be passed easily.
Actually, syzbot caught this by passing some zero'ed old hw_params
ioctl.

So, having snd_BUG_ON() there is simply superfluous and rather
harmful to give unnecessary confusions. Let's get rid of it.

Reported-by: syzbot+7e6ee5...@syzkaller.appspotmail.com
Cc: <sta...@vger.kernel.org>
Signed-off-by: Takashi Iwai <ti...@suse.de>
---
sound/core/pcm_lib.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index db7894bb028c..faa67861cbc1 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -560,7 +560,6 @@ static inline unsigned int muldiv32(unsigned int a, unsigned int b,
{
u_int64_t n = (u_int64_t) a * b;
if (c == 0) {
- snd_BUG_ON(!n);
*r = 0;
return UINT_MAX;
}
--
2.15.1