[PATCH 4.15 150/163] ALSA: seq: Fix racy pool initializations

Greg Kroah-Hartman
2018-02-21T12:49:39Z

From: Takashi Iwai <tiwai@suse.de>

commit d15d662e89fc667b90cd294b0eb45694e33144da upstream.

ALSA sequencer core initializes the event pool on demand by invoking
snd_seq_pool_init() when the first write happens and the pool is
empty. Meanwhile user can reset the pool size manually via ioctl
concurrently, and this may lead to UAF or out-of-bound accesses since
the function tries to vmalloc / vfree the buffer.

A simple fix is to just wrap the snd_seq_pool_init() call with the
recently introduced client->ioctl_mutex; as the calls for
snd_seq_pool_init() from other side are always protected with this
mutex, we can avoid the race.

Reported-by: 范龙飞 <long7573@126.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/core/seq/seq_clientmgr.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1003,7 +1003,7 @@ static ssize_t snd_seq_write(struct file
{
struct snd_seq_client *client = file->private_data;
int written = 0, len;
- int err = -EINVAL;
+ int err;
struct snd_seq_event event;

if (!(snd_seq_file_flags(file) & SNDRV_SEQ_LFLG_OUTPUT))
@@ -1018,11 +1018,15 @@ static ssize_t snd_seq_write(struct file

/* allocate the pool now if the pool is not allocated yet */
if (client->pool->size > 0 && !snd_seq_write_pool_allocated(client)) {
- if (snd_seq_pool_init(client->pool) < 0)
+ mutex_lock(&client->ioctl_mutex);
+ err = snd_seq_pool_init(client->pool);
+ mutex_unlock(&client->ioctl_mutex);
+ if (err < 0)
return -ENOMEM;
}

/* only process whole events */
+ err = -EINVAL;
while (count >= sizeof(struct snd_seq_event)) {
/* Read in the event header from the user */
len = sizeof(event);