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Commit 2cdc7b63 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: seq: Fix yet another races among ALSA timer accesses 

ALSA sequencer may open/close and control ALSA timer instance
dynamically either via sequencer events or direct ioctls.  These are
done mostly asynchronously, and it may call still some timer action
like snd_timer_start() while another is calling snd_timer_close().
Since the instance gets removed by snd_timer_close(), it may lead to
a use-after-free.

This patch tries to address such a race by protecting each
snd_timer_*() call via the existing spinlock and also by avoiding the
access to timer during close call.

BugLink: http://lkml.kernel.org/r/CACT4Y+Z6RzW5MBr-HUdV-8zwg71WQfKTdPpYGvOeS7v4cyurNQ@mail.gmail.com


Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent b2483716

sound/core/seq/seq_timer.c

+67 −20
Original line number Diff line number Diff line
@@ -90,6 +90,9 @@ void snd_seq_timer_delete(struct snd_seq_timer **tmr) 


void snd_seq_timer_defaults(struct snd_seq_timer * tmr)

{

	unsigned long flags;



	spin_lock_irqsave(&tmr->lock, flags);

	/* setup defaults */

	tmr->ppq = 96;		/* 96 PPQ */

	tmr->tempo = 500000;	/* 120 BPM */
@@ -105,21 +108,25 @@ void snd_seq_timer_defaults(struct snd_seq_timer * tmr) 
	tmr->preferred_resolution = seq_default_timer_resolution;



	tmr->skew = tmr->skew_base = SKEW_BASE;

	spin_unlock_irqrestore(&tmr->lock, flags);

}



void snd_seq_timer_reset(struct snd_seq_timer * tmr)

static void seq_timer_reset(struct snd_seq_timer *tmr)

{

	unsigned long flags;



	spin_lock_irqsave(&tmr->lock, flags);



	/* reset time & songposition */

	tmr->cur_time.tv_sec = 0;

	tmr->cur_time.tv_nsec = 0;



	tmr->tick.cur_tick = 0;

	tmr->tick.fraction = 0;

}



void snd_seq_timer_reset(struct snd_seq_timer *tmr)

{

	unsigned long flags;



	spin_lock_irqsave(&tmr->lock, flags);

	seq_timer_reset(tmr);

	spin_unlock_irqrestore(&tmr->lock, flags);

}
@@ -138,8 +145,11 @@ static void snd_seq_timer_interrupt(struct snd_timer_instance *timeri, 
	tmr = q->timer;

	if (tmr == NULL)

		return;

	if (!tmr->running)

	spin_lock_irqsave(&tmr->lock, flags);

	if (!tmr->running) {

		spin_unlock_irqrestore(&tmr->lock, flags);

		return;

	}



	resolution *= ticks;

	if (tmr->skew != tmr->skew_base) {
@@ -148,8 +158,6 @@ static void snd_seq_timer_interrupt(struct snd_timer_instance *timeri, 
			(((resolution & 0xffff) * tmr->skew) >> 16);

	}



	spin_lock_irqsave(&tmr->lock, flags);



	/* update timer */

	snd_seq_inc_time_nsec(&tmr->cur_time, resolution);
@@ -296,26 +304,30 @@ int snd_seq_timer_open(struct snd_seq_queue *q) 
	t->callback = snd_seq_timer_interrupt;

	t->callback_data = q;

	t->flags |= SNDRV_TIMER_IFLG_AUTO;

	spin_lock_irq(&tmr->lock);

	tmr->timeri = t;

	spin_unlock_irq(&tmr->lock);

	return 0;

}



int snd_seq_timer_close(struct snd_seq_queue *q)

{

	struct snd_seq_timer *tmr;

	struct snd_timer_instance *t;

	

	tmr = q->timer;

	if (snd_BUG_ON(!tmr))

		return -EINVAL;

	if (tmr->timeri) {

		snd_timer_stop(tmr->timeri);

		snd_timer_close(tmr->timeri);

	spin_lock_irq(&tmr->lock);

	t = tmr->timeri;

	tmr->timeri = NULL;

	}

	spin_unlock_irq(&tmr->lock);

	if (t)

		snd_timer_close(t);

	return 0;

}



int snd_seq_timer_stop(struct snd_seq_timer * tmr)

static int seq_timer_stop(struct snd_seq_timer *tmr)

{

	if (! tmr->timeri)

		return -EINVAL;
@@ -326,6 +338,17 @@ int snd_seq_timer_stop(struct snd_seq_timer * tmr) 
	return 0;

}



int snd_seq_timer_stop(struct snd_seq_timer *tmr)

{

	unsigned long flags;

	int err;



	spin_lock_irqsave(&tmr->lock, flags);

	err = seq_timer_stop(tmr);

	spin_unlock_irqrestore(&tmr->lock, flags);

	return err;

}



static int initialize_timer(struct snd_seq_timer *tmr)

{

	struct snd_timer *t;
@@ -358,13 +381,13 @@ static int initialize_timer(struct snd_seq_timer *tmr) 
	return 0;

}



int snd_seq_timer_start(struct snd_seq_timer * tmr)

static int seq_timer_start(struct snd_seq_timer *tmr)

{

	if (! tmr->timeri)

		return -EINVAL;

	if (tmr->running)

		snd_seq_timer_stop(tmr);

	snd_seq_timer_reset(tmr);

		seq_timer_stop(tmr);

	seq_timer_reset(tmr);

	if (initialize_timer(tmr) < 0)

		return -EINVAL;

	snd_timer_start(tmr->timeri, tmr->ticks);
@@ -373,14 +396,25 @@ int snd_seq_timer_start(struct snd_seq_timer * tmr) 
	return 0;

}



int snd_seq_timer_continue(struct snd_seq_timer * tmr)

int snd_seq_timer_start(struct snd_seq_timer *tmr)

{

	unsigned long flags;

	int err;



	spin_lock_irqsave(&tmr->lock, flags);

	err = seq_timer_start(tmr);

	spin_unlock_irqrestore(&tmr->lock, flags);

	return err;

}



static int seq_timer_continue(struct snd_seq_timer *tmr)

{

	if (! tmr->timeri)

		return -EINVAL;

	if (tmr->running)

		return -EBUSY;

	if (! tmr->initialized) {

		snd_seq_timer_reset(tmr);

		seq_timer_reset(tmr);

		if (initialize_timer(tmr) < 0)

			return -EINVAL;

	}
@@ -390,11 +424,24 @@ int snd_seq_timer_continue(struct snd_seq_timer * tmr) 
	return 0;

}



int snd_seq_timer_continue(struct snd_seq_timer *tmr)

{

	unsigned long flags;

	int err;



	spin_lock_irqsave(&tmr->lock, flags);

	err = seq_timer_continue(tmr);

	spin_unlock_irqrestore(&tmr->lock, flags);

	return err;

}



/* return current 'real' time. use timeofday() to get better granularity. */

snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr)

{

	snd_seq_real_time_t cur_time;

	unsigned long flags;



	spin_lock_irqsave(&tmr->lock, flags);

	cur_time = tmr->cur_time;

	if (tmr->running) { 

		struct timeval tm;
@@ -410,7 +457,7 @@ snd_seq_real_time_t snd_seq_timer_get_cur_time(struct snd_seq_timer *tmr) 
		}

		snd_seq_sanity_real_time(&cur_time);

	}

                

	spin_unlock_irqrestore(&tmr->lock, flags);

	return cur_time;	

}