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authorTakashi Iwai <tiwai@suse.de>2018-03-09 21:58:28 +0100
committerTakashi Iwai <tiwai@suse.de>2018-03-10 17:29:49 +0100
commitd0f833065221cbfcbadf19fd4102bcfa9330006a (patch)
treee4ebd38d4fe20596abb36a83f27fa6c29985c0c9 /sound
parent099fd6ca0ad25bc19c5ade2ea4b25b8fadaa11b3 (diff)
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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: Nicolai Stange <nstange@suse.de> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/seq/seq_prioq.c28
-rw-r--r--sound/core/seq/seq_prioq.h6
-rw-r--r--sound/core/seq/seq_queue.c28
3 files changed, 25 insertions, 37 deletions
diff --git a/sound/core/seq/seq_prioq.c b/sound/core/seq/seq_prioq.c
index bc1c8488fc2a..2bc6759e4adc 100644
--- a/sound/core/seq/seq_prioq.c
+++ b/sound/core/seq/seq_prioq.c
@@ -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)
{
diff --git a/sound/core/seq/seq_prioq.h b/sound/core/seq/seq_prioq.h
index d38bb78d9345..2c315ca10fc4 100644
--- a/sound/core/seq/seq_prioq.h
+++ b/sound/core/seq/seq_prioq.h
@@ -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);
diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c
index 0428e9061b47..b377f5048352 100644
--- a/sound/core/seq/seq_queue.c
+++ b/sound/core/seq/seq_queue.c
@@ -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 */