Commit d0f83306 authored by Takashi Iwai's avatar Takashi Iwai

ALSA: seq: Fix possible UAF in snd_seq_check_queue()

Although we've covered the races between concurrent write() and
ioctl() in the previous patch series, there is still a possible UAF in
the following scenario:

A: user client closed		B: timer irq
  -> snd_seq_release()		  -> snd_seq_timer_interrupt()
    -> snd_seq_free_client()	    -> snd_seq_check_queue()
				      -> cell = snd_seq_prioq_cell_peek()
      -> snd_seq_prioq_leave()
         .... removing all cells
      -> snd_seq_pool_done()
         .... vfree()
				      -> snd_seq_compare_tick_time(cell)
				         ... Oops

So the problem is that a cell is peeked and accessed without any
protection until it's retrieved from the queue again via
snd_seq_prioq_cell_out().

This patch tries to address it, also cleans up the code by a slight
refactoring.  snd_seq_prioq_cell_out() now receives an extra pointer
argument.  When it's non-NULL, the function checks the event timestamp
with the given pointer.  The caller needs to pass the right reference
either to snd_seq_tick or snd_seq_realtime depending on the event
timestamp type.

A good news is that the above change allows us to remove the
snd_seq_prioq_cell_peek(), too, thus the patch actually reduces the
code size.
Reviewed-by: default avatarNicolai Stange <nstange@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 099fd6ca
......@@ -87,7 +87,7 @@ void snd_seq_prioq_delete(struct snd_seq_prioq **fifo)
if (f->cells > 0) {
/* drain prioQ */
while (f->cells > 0)
snd_seq_cell_free(snd_seq_prioq_cell_out(f));
snd_seq_cell_free(snd_seq_prioq_cell_out(f, NULL));
}
kfree(f);
......@@ -214,8 +214,18 @@ int snd_seq_prioq_cell_in(struct snd_seq_prioq * f,
return 0;
}
/* return 1 if the current time >= event timestamp */
static int event_is_ready(struct snd_seq_event *ev, void *current_time)
{
if ((ev->flags & SNDRV_SEQ_TIME_STAMP_MASK) == SNDRV_SEQ_TIME_STAMP_TICK)
return snd_seq_compare_tick_time(current_time, &ev->time.tick);
else
return snd_seq_compare_real_time(current_time, &ev->time.time);
}
/* dequeue cell from prioq */
struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f)
struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f,
void *current_time)
{
struct snd_seq_event_cell *cell;
unsigned long flags;
......@@ -227,6 +237,8 @@ struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f)
spin_lock_irqsave(&f->lock, flags);
cell = f->head;
if (cell && current_time && !event_is_ready(&cell->event, current_time))
cell = NULL;
if (cell) {
f->head = cell->next;
......@@ -252,18 +264,6 @@ int snd_seq_prioq_avail(struct snd_seq_prioq * f)
return f->cells;
}
/* peek at cell at the head of the prioq */
struct snd_seq_event_cell *snd_seq_prioq_cell_peek(struct snd_seq_prioq * f)
{
if (f == NULL) {
pr_debug("ALSA: seq: snd_seq_prioq_cell_in() called with NULL prioq\n");
return NULL;
}
return f->head;
}
static inline int prioq_match(struct snd_seq_event_cell *cell,
int client, int timestamp)
{
......
......@@ -44,14 +44,12 @@ void snd_seq_prioq_delete(struct snd_seq_prioq **fifo);
int snd_seq_prioq_cell_in(struct snd_seq_prioq *f, struct snd_seq_event_cell *cell);
/* dequeue cell from prioq */
struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f);
struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f,
void *current_time);
/* return number of events available in prioq */
int snd_seq_prioq_avail(struct snd_seq_prioq *f);
/* peek at cell at the head of the prioq */
struct snd_seq_event_cell *snd_seq_prioq_cell_peek(struct snd_seq_prioq *f);
/* client left queue */
void snd_seq_prioq_leave(struct snd_seq_prioq *f, int client, int timestamp);
......
......@@ -277,30 +277,20 @@ void snd_seq_check_queue(struct snd_seq_queue *q, int atomic, int hop)
__again:
/* Process tick queue... */
while ((cell = snd_seq_prioq_cell_peek(q->tickq)) != NULL) {
if (snd_seq_compare_tick_time(&q->timer->tick.cur_tick,
&cell->event.time.tick)) {
cell = snd_seq_prioq_cell_out(q->tickq);
if (cell)
snd_seq_dispatch_event(cell, atomic, hop);
} else {
/* event remains in the queue */
for (;;) {
cell = snd_seq_prioq_cell_out(q->tickq,
&q->timer->tick.cur_tick);
if (!cell)
break;
}
snd_seq_dispatch_event(cell, atomic, hop);
}
/* Process time queue... */
while ((cell = snd_seq_prioq_cell_peek(q->timeq)) != NULL) {
if (snd_seq_compare_real_time(&q->timer->cur_time,
&cell->event.time.time)) {
cell = snd_seq_prioq_cell_out(q->timeq);
if (cell)
snd_seq_dispatch_event(cell, atomic, hop);
} else {
/* event remains in the queue */
for (;;) {
cell = snd_seq_prioq_cell_out(q->timeq, &q->timer->cur_time);
if (!cell)
break;
}
snd_seq_dispatch_event(cell, atomic, hop);
}
/* free lock */
......
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