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authorTakashi Iwai <tiwai@suse.de>2016-09-07 15:45:31 +0200
committerTakashi Iwai <tiwai@suse.de>2016-09-08 10:45:05 +0200
commit9f8a7658bcafb2a7853f7a2eae8a94e87e6e695b (patch)
tree73f43bb689b5b319d22e43909eff5cb5277bea77 /sound
parent11749e086b2766cccf6217a527ef5c5604ba069c (diff)
downloadlinux-stericsson-9f8a7658bcafb2a7853f7a2eae8a94e87e6e695b.tar.gz
ALSA: timer: Fix zero-division by continue of uninitialized instance
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>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/timer.c14
1 files changed, 14 insertions, 0 deletions
diff --git a/sound/core/timer.c b/sound/core/timer.c
index 2706061fc1ea..fc144f43faa6 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
#else
@@ -539,6 +542,10 @@ 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_CONTINUE);
unlock:
@@ -600,6 +607,10 @@ 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
@@ -1831,6 +1842,9 @@ 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;
}