sound: divide by 0 in snd_hrtimer_callback (or hang)

From: Dmitry Vyukov
Date: Sat Sep 03 2016 - 08:35:43 EST

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Hello,

The following program causes either division error or hangs kernel:

https://gist.githubusercontent.com/dvyukov/b1f33be3bfcc15d629e10db483bee1e4/raw/1574b407e0456bf8277bee423e7731641f5f2c14/gistfile1.txt

divide error: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 27320 Comm: syz-executor Not tainted 4.8.0-rc3-next-20160825+ #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88003c9b2280 task.stack: ffff880027280000
RIP: 0010:[<ffffffff858e1a6c>] [< inline >] ktime_divns
include/linux/ktime.h:195
RIP: 0010:[<ffffffff858e1a6c>] [<ffffffff858e1a6c>]
snd_hrtimer_callback+0x1bc/0x3c0 sound/core/hrtimer.c:62
RSP: 0018:ffff88003ed07dd8 EFLAGS: 00010006
RAX: 0000000000004801 RBX: ffff88003d3a0a88 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff88003d3a0aa0 RDI: ffffffff886b69a8
RBP: ffff88003ed07e30 R08: 0000010e85417665 R09: ffff88007fff7048
R10: ffff88007fff7058 R11: ffff88007fff7050 R12: ffff88003d00f840
R13: ffff88003d00f8f4 R14: ffff88003d00f970 R15: ffff88003d3a0a80
FS: 0000000000000000(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4152126db8 CR3: 000000006b896000 CR4: 00000000000006e0
DR0: 000000000000001e DR1: 000000000000001e DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
0000000000000000 ffff88003d3a0aa0 ffff88003d00f8f8 0000000000004801
ffff88003d3a0ae0 0000000000000000 ffff88003d3a0a88 0000000000000001
ffff88003ed1b400 dffffc0000000000 0000000000000001 ffff88003ed07f28
Call Trace:
<IRQ>
[< inline >] __run_hrtimer kernel/time/hrtimer.c:1238
[<ffffffff81504335>] __hrtimer_run_queues+0x325/0xe70
kernel/time/hrtimer.c:1302
[<ffffffff81506ceb>] hrtimer_interrupt+0x18b/0x420 kernel/time/hrtimer.c:1336
[<ffffffff8126d8df>] local_apic_timer_interrupt+0x6f/0xe0
arch/x86/kernel/apic/apic.c:933
[<ffffffff86e13056>] smp_apic_timer_interrupt+0x76/0xa0
arch/x86/kernel/apic/apic.c:957
[<ffffffff86e1210c>] apic_timer_interrupt+0x8c/0xa0
arch/x86/entry/entry_64.S:487
<EOI>
[< inline >] rcu_lock_release include/linux/rcupdate.h:494
[< inline >] rcu_read_unlock include/linux/rcupdate.h:927
[<ffffffff81839f55>] unlock_page_memcg+0x95/0x130 mm/memcontrol.c:1680
[< inline >] page_remove_file_rmap mm/rmap.c:1343
[<ffffffff817b742c>] page_remove_rmap+0x1cc/0x8e0 mm/rmap.c:1394
[< inline >] zap_pte_range mm/memory.c:1170
[< inline >] zap_pmd_range mm/memory.c:1257
[< inline >] zap_pud_range mm/memory.c:1278
[<ffffffff81789119>] unmap_page_range+0xf89/0x1ba0 mm/memory.c:1299
[<ffffffff81789e31>] unmap_single_vma+0x101/0x260 mm/memory.c:1344
[<ffffffff8178a741>] unmap_vmas+0xf1/0x1b0
[<ffffffff817a5aab>] exit_mmap+0x22b/0x420 mm/mmap.c:2787
[< inline >] __mmput kernel/fork.c:770
[<ffffffff8137c576>] mmput+0xd6/0x3c0 kernel/fork.c:790
[< inline >] exit_mm kernel/exit.c:512
[<ffffffff813940e8>] do_exit+0x738/0x2e70 kernel/exit.c:815
[<ffffffff81396998>] do_group_exit+0x108/0x330 kernel/exit.c:958
[<ffffffff813ba4aa>] get_signal+0x62a/0x15d0 kernel/signal.c:2307
[<ffffffff81202333>] do_signal+0x83/0x1f60 arch/x86/kernel/signal.c:805
[<ffffffff81006345>] exit_to_usermode_loop+0x1a5/0x210
arch/x86/entry/common.c:163
[< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:198
[< inline >] syscall_return_slowpath arch/x86/entry/common.c:267
[<ffffffff81008be0>] do_syscall_64+0x4c0/0x640 arch/x86/entry/common.c:293
[<ffffffff86e107c3>] entry_SYSCALL64_slow_path+0x25/0x25
Code: cb a2 ce fb 8b 0d f5 21 70 05 48 0f af 4d d0 48 85 c9 0f 88 6a
01 00 00 48 89 4d a8 e8 ae a2 ce fb 48 8b 45 c0 48 8b 4d a8 48 99 <48>
f7 f9 48 01 45 d0 e8 98 a2 ce fb 4c 89 fa 48 b8 00 00 00 00
RIP [< inline >] ktime_divns include/linux/ktime.h:195
RIP [<ffffffff858e1a6c>] snd_hrtimer_callback+0x1bc/0x3c0
sound/core/hrtimer.c:62
RSP <ffff88003ed07dd8>
---[ end trace e1a6d1e5a6136d50 ]---

or:

INFO: rcu_sched detected stalls on CPUs/tasks:
0-...: (1 GPs behind) idle=203/140000000000001/0 softirq=923090/923091 fqs=6490
(detected by 1, t=26002 jiffies, g=508022, c=508021, q=20)
Task dump for CPU 0:
a.out R running task 28848 31756 4047 0x0000000a
0000000000000000 0000000000000282 0000000000000000 ffff880066a9b430
ffff880066a9b430 ffff8800667cfae0 0000000000000282 0000000000000000
0000000000000000 0000000000000000 000003a0184674dd dffffc0000000000
Call Trace:
[< inline >] spin_unlock_irqrestore ./include/linux/spinlock.h:362
[<ffffffff858db3dd>] snd_timer_start1+0xdd/0x740 sound/core/timer.c:477
[<ffffffff858dbb25>] snd_timer_continue+0x45/0x80 sound/core/timer.c:606
[< inline >] snd_timer_user_continue sound/core/timer.c:1835
[< inline >] __snd_timer_user_ioctl sound/core/timer.c:1902
[<ffffffff858df299>] snd_timer_user_ioctl+0xe99/0x2470 sound/core/timer.c:1917
[< inline >] vfs_ioctl fs/ioctl.c:43
[<ffffffff818a1dfc>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675
[< inline >] SYSC_ioctl fs/ioctl.c:690
[<ffffffff818a2d7f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681
[<ffffffff86e10700>] entry_SYSCALL_64_fastpath+0x23/0xc1
arch/x86/entry/entry_64.S:208

I am on 0f98f121e1670eaa2a2fbb675e07d6ba7f0e146f of linux-next with
the following diff in sound/core/timer.c (one is a fix for another
division by 0):

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 9a6157e..3e55c6d 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -813,6 +813,7 @@ int snd_timer_new(struct snd_card *card, char *id,
struct snd_timer_id *tid,
timer->tmr_subdevice = tid->subdevice;
if (id)
strlcpy(timer->id, id, sizeof(timer->id));
+ timer->sticks = 1;
INIT_LIST_HEAD(&timer->device_list);
INIT_LIST_HEAD(&timer->open_list_head);
INIT_LIST_HEAD(&timer->active_list_head);
@@ -1958,6 +1959,7 @@ static ssize_t snd_timer_user_read(struct file
*file, char __user *buffer,
tu->qused--;
spin_unlock_irq(&tu->qlock);

+ mutex_lock(&tu->ioctl_lock);
if (tu->tread) {
if (copy_to_user(buffer, &tu->tqueue[qhead],
sizeof(struct snd_timer_tread)))
@@ -1967,6 +1969,7 @@ static ssize_t snd_timer_user_read(struct file
*file, char __user *buffer,
sizeof(struct snd_timer_read)))
err = -EFAULT;
}
+ mutex_unlock(&tu->ioctl_lock);

spin_lock_irq(&tu->qlock);
if (err < 0)

Next message: Peter Zijlstra: "Re: How does the size field work in IOCTL numbers?"
Previous message: SF Markus Elfring: "[PATCH 14/17] s390/debug: Improve a size determination in debug_sprintf_format_fn()"
Next in thread: Takashi Iwai: "Re: sound: divide by 0 in snd_hrtimer_callback (or hang)"
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