Skip to content

Commit

Permalink
ALSA: seq: Fix yet another races among ALSA timer accesses
Browse files Browse the repository at this point in the history 
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: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
  • Loading branch information
Takashi Iwai committed Feb 1, 2016
1 parent b248371 commit 2cdc7b6
Showing 1 changed file with 67 additions and 20 deletions.
87 changes: 67 additions & 20 deletions sound/core/seq/seq_timer.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand All @@ -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);
}

Expand All @@ -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) {
Expand All @@ -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);

Expand Down Expand Up @@ -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);
tmr->timeri = NULL;
}
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;
Expand All @@ -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;
Expand Down Expand Up @@ -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);
Expand All @@ -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;
}
Expand All @@ -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;
Expand All @@ -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;
}

Expand Down

0 comments on commit 2cdc7b6

Please sign in to comment.