[PATCH AUTOSEL 4.4 41/65] ALSA: timer: Fix zero-division by continue of uninitialized instance

Sasha Levin
2018-10-25T14:18:16Z

From: Takashi Iwai <tiwai@suse.de>

[ Upstream commit 9f8a7658bcafb2a7853f7a2eae8a94e87e6e695b ]

When a user timer instance is continued without the explicit start
beforehand, the system gets eventually zero-division error like:

divide error: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
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
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>
.....

Although a similar issue was spotted and a fix patch was merged in
commit [6b760bb2c63a: ALSA: timer: fix division by zero after
SNDRV_TIMER_IOCTL_CONTINUE], it seems covering only a part of
iceberg.

In this patch, we fix the issue a bit more drastically. Basically the
continue of an uninitialized timer is supposed to be a fresh start, so
we do it for user timers. For the direct snd_timer_continue() call,
there is no way to pass the initial tick value, so we kick out for the
uninitialized case.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
sound/core/timer.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index ef850a99d64a..f989adb98a22 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -35,6 +35,9 @@
#include <sound/initval.h>
#include <linux/kmod.h>

+/* internal flags */
+#define SNDRV_TIMER_IFLG_PAUSED 0x00010000
+
#if IS_ENABLED(CONFIG_SND_HRTIMER)
#define DEFAULT_TIMER_LIMIT 4
#elif IS_ENABLED(CONFIG_SND_RTCTIMER)
@@ -547,6 +550,10 @@ static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop)
}
}
timeri->flags &= ~(SNDRV_TIMER_IFLG_RUNNING | SNDRV_TIMER_IFLG_START);
+ if (stop)
+ timeri->flags &= ~SNDRV_TIMER_IFLG_PAUSED;
+ else
+ timeri->flags |= SNDRV_TIMER_IFLG_PAUSED;
snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
SNDRV_TIMER_EVENT_PAUSE);
unlock:
@@ -608,6 +615,10 @@ int snd_timer_stop(struct snd_timer_instance *timeri)
*/
int snd_timer_continue(struct snd_timer_instance *timeri)
{
+ /* timer can continue only after pause */
+ if (!(timeri->flags & SNDRV_TIMER_IFLG_PAUSED))
+ return -EINVAL;
+
if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE)
return snd_timer_start_slave(timeri, false);
else
@@ -1837,6 +1848,9 @@ static int snd_timer_user_continue(struct file *file)
tu = file->private_data;
if (!tu->timeri)
return -EBADFD;
+ /* start timer instead of continue if it's not used before */
+ if (!(tu->timeri->flags & SNDRV_TIMER_IFLG_PAUSED))
+ return snd_timer_user_start(file);
tu->timeri->lost = 0;
return (err = snd_timer_continue(tu->timeri)) < 0 ? err : 0;
}
--
2.17.1