From cf1533f9669664757084a09ed37695d9fe1d14c9 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Wed, 7 Sep 2016 15:45:31 +0200 Subject: [PATCH] ALSA: timer: Fix zero-division by continue of uninitialized instance commit 9f8a7658bcafb2a7853f7a2eae8a94e87e6e695b upstream. 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:[] [< inline >] ktime_divns include/linux/ktime.h:195 RIP: 0010:[] [] snd_hrtimer_callback+0x1bc/0x3c0 sound/core/hrtimer.c:62 Call Trace: [< inline >] __run_hrtimer kernel/time/hrtimer.c:1238 [] __hrtimer_run_queues+0x325/0xe70 kernel/time/hrtimer.c:1302 [] hrtimer_interrupt+0x18b/0x420 kernel/time/hrtimer.c:1336 [] local_apic_timer_interrupt+0x6f/0xe0 arch/x86/kernel/apic/apic.c:933 [] smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:957 [] apic_timer_interrupt+0x8c/0xa0 arch/x86/entry/entry_64.S:487 ..... 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 Signed-off-by: Takashi Iwai [bwh: Backported to 3.2: - Adjust context - In _snd_timer_stop(), check the value of 'event' instead of 'stop'] Signed-off-by: Ben Hutchings --- sound/core/timer.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/sound/core/timer.c b/sound/core/timer.c index ffecc44179cf..5628b6548d18 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -34,6 +34,9 @@ #include #include +/* internal flags */ +#define SNDRV_TIMER_IFLG_PAUSED 0x00010000 + #if defined(CONFIG_SND_HRTIMER) || defined(CONFIG_SND_HRTIMER_MODULE) #define DEFAULT_TIMER_LIMIT 4 #elif defined(CONFIG_SND_RTCTIMER) || defined(CONFIG_SND_RTCTIMER_MODULE) @@ -552,6 +555,10 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event) } } timeri->flags &= ~(SNDRV_TIMER_IFLG_RUNNING | SNDRV_TIMER_IFLG_START); + if (event == SNDRV_TIMER_EVENT_STOP) + timeri->flags &= ~SNDRV_TIMER_IFLG_PAUSED; + else + timeri->flags |= SNDRV_TIMER_IFLG_PAUSED; spin_unlock_irqrestore(&timer->lock, flags); __end: if (event != SNDRV_TIMER_EVENT_RESOLUTION) @@ -594,6 +601,10 @@ int snd_timer_continue(struct snd_timer_instance *timeri) if (timeri == NULL) return result; + /* 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); timer = timeri->timer; @@ -1798,6 +1809,9 @@ 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; } -- 2.47.2