Code: static void snd_timer_user_tinterrupt(struct snd_timer_instance *timeri,
				      unsigned long resolution,
				      unsigned long ticks)
{
	struct snd_timer_user *tu = timeri->callback_data;
	struct snd_timer_tread *r, r1;
	struct timespec tstamp;
	int prev, append = 0;

	memset(&tstamp, 0, sizeof(tstamp));
	spin_lock(&tu->qlock);
	if ((tu->filter & ((1 << SNDRV_TIMER_EVENT_RESOLUTION) |
			   (1 << SNDRV_TIMER_EVENT_TICK))) == 0) {
		spin_unlock(&tu->qlock);
		return;
	}
	if (tu->last_resolution != resolution || ticks > 0) {
		if (timer_tstamp_monotonic)
			ktime_get_ts(&tstamp);
		else
			getnstimeofday(&tstamp);
 	}
 	if ((tu->filter & (1 << SNDRV_TIMER_EVENT_RESOLUTION)) &&
 	    tu->last_resolution != resolution) {
 		r1.event = SNDRV_TIMER_EVENT_RESOLUTION;
 		r1.tstamp = tstamp;
 		r1.val = resolution;
		snd_timer_user_append_to_tqueue(tu, &r1);
		tu->last_resolution = resolution;
		append++;
	}
	if ((tu->filter & (1 << SNDRV_TIMER_EVENT_TICK)) == 0)
		goto __wake;
	if (ticks == 0)
		goto __wake;
	if (tu->qused > 0) {
		prev = tu->qtail == 0 ? tu->queue_size - 1 : tu->qtail - 1;
		r = &tu->tqueue[prev];
		if (r->event == SNDRV_TIMER_EVENT_TICK) {
			r->tstamp = tstamp;
			r->val += ticks;
			append++;
			goto __wake;
		}
	}
	r1.event = SNDRV_TIMER_EVENT_TICK;
	r1.tstamp = tstamp;
	r1.val = ticks;
	snd_timer_user_append_to_tqueue(tu, &r1);
	append++;
      __wake:
	spin_unlock(&tu->qlock);
	if (append == 0)
		return;
	kill_fasync(&tu->fasync, SIGIO, POLL_IN);
	wake_up(&tu->qchange_sleep);
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: sound/core/timer.c in the Linux kernel through 4.6 does not initialize certain r1 data structures, which allows local users to obtain sensitive information from kernel stack memory via crafted use of the ALSA timer interface, related to the (1) snd_timer_user_ccallback and (2) snd_timer_user_tinterrupt functions.
Commit Message: ALSA: timer: Fix leak in events via snd_timer_user_tinterrupt

The stack object “r1” has a total size of 32 bytes. Its field
“event” and “val” both contain 4 bytes padding. These 8 bytes
padding bytes are sent to user without being initialized.

Signed-off-by: Kangjie Lu <kjlu@gatech.edu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>