On Wed, 10 Jan 2018 19:58:01 +0100, syzbot wrote:
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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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
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 tiwai@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+7e6ee55011deeebce15d@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@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; }