[PATCH 1/2] ALSA: seq: Fix yet another races among ALSA timer accesses

From: Takashi Iwai
Date: Sat Jan 30 2016 - 17:30:25 EST

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@xxxxxxxxxxxxxx
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
sound/core/seq/seq_timer.c | 87 +++++++++++++++++++++++++++++++++++-----------
1 file changed, 67 insertions(+), 20 deletions(-)

diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
index 82b220c769c1..293104926098 100644
--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -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);
- 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;
@@ -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;
}

--
2.7.0


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