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Message-ID: <lsq.1528380321.340415478@decadent.org.uk>
Date: Thu, 07 Jun 2018 15:05:21 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, "Nicolai Stange" <nstange@...e.de>,
"Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.16 342/410] ALSA: seq: Fix possible UAF in
snd_seq_check_queue()
3.16.57-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Takashi Iwai <tiwai@...e.de>
commit d0f833065221cbfcbadf19fd4102bcfa9330006a upstream.
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@...e.de>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
sound/core/seq/seq_prioq.c | 28 ++++++++++++++--------------
sound/core/seq/seq_prioq.h | 6 ++----
sound/core/seq/seq_queue.c | 28 +++++++++-------------------
3 files changed, 25 insertions(+), 37 deletions(-)
--- 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
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
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
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_p
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)
{
--- 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
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);
--- a/sound/core/seq/seq_queue.c
+++ b/sound/core/seq/seq_queue.c
@@ -273,30 +273,20 @@ void snd_seq_check_queue(struct snd_seq_
__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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