From 4842e98f26dd80be3623c4714a244ba52ea096a8 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Wed, 8 Feb 2017 12:35:39 +0100 Subject: [PATCH] ALSA: seq: Fix race at creating a queue When a sequencer queue is created in snd_seq_queue_alloc(),it adds the new queue element to the public list before referencing it. Thus the queue might be deleted before the call of snd_seq_queue_use(), and it results in the use-after-free error, as spotted by syzkaller. The fix is to reference the queue object at the right time. Reported-by: Dmitry Vyukov Cc: Signed-off-by: Takashi Iwai --- sound/core/seq/seq_queue.c | 33 ++++++++++++++++++++------------- 1 file changed, 20 insertions(+), 13 deletions(-) diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c index 0bec02e89d51..450c5187eecb 100644 --- a/sound/core/seq/seq_queue.c +++ b/sound/core/seq/seq_queue.c @@ -181,6 +181,8 @@ void __exit snd_seq_queues_delete(void) } } +static void queue_use(struct snd_seq_queue *queue, int client, int use); + /* allocate a new queue - * return queue index value or negative value for error */ @@ -192,11 +194,11 @@ int snd_seq_queue_alloc(int client, int locked, unsigned int info_flags) if (q == NULL) return -ENOMEM; q->info_flags = info_flags; + queue_use(q, client, 1); if (queue_list_add(q) < 0) { queue_delete(q); return -ENOMEM; } - snd_seq_queue_use(q->queue, client, 1); /* use this queue */ return q->queue; } @@ -502,19 +504,9 @@ int snd_seq_queue_timer_set_tempo(int queueid, int client, return result; } - -/* use or unuse this queue - - * if it is the first client, starts the timer. - * if it is not longer used by any clients, stop the timer. - */ -int snd_seq_queue_use(int queueid, int client, int use) +/* use or unuse this queue */ +static void queue_use(struct snd_seq_queue *queue, int client, int use) { - struct snd_seq_queue *queue; - - queue = queueptr(queueid); - if (queue == NULL) - return -EINVAL; - mutex_lock(&queue->timer_mutex); if (use) { if (!test_and_set_bit(client, queue->clients_bitmap)) queue->clients++; @@ -529,6 +521,21 @@ int snd_seq_queue_use(int queueid, int client, int use) } else { snd_seq_timer_close(queue); } +} + +/* use or unuse this queue - + * if it is the first client, starts the timer. + * if it is not longer used by any clients, stop the timer. + */ +int snd_seq_queue_use(int queueid, int client, int use) +{ + struct snd_seq_queue *queue; + + queue = queueptr(queueid); + if (queue == NULL) + return -EINVAL; + mutex_lock(&queue->timer_mutex); + queue_use(queue, client, use); mutex_unlock(&queue->timer_mutex); queuefree(queue); return 0; -- 2.20.1