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ALSA: seq: Don't allow resizing pool in use
This is a fix for a (sort of) fallout in the recent commitd15d662e89
("ALSA: seq: Fix racy pool initializations") for CVE-2018-1000004. As the pool resize deletes the existing cells, it may lead to a race when another thread is writing concurrently, eventually resulting a UAF. A simple workaround is not to allow the pool resizing when the pool is in use. It's an invalid behavior in anyway. Fixes:d15d662e89
("ALSA: seq: Fix racy pool initializations") Reported-by: 范龙飞 <long7573@126.com> Reported-by: Nicolai Stange <nstange@suse.de> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
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@ -1838,6 +1838,9 @@ static int snd_seq_ioctl_set_client_pool(struct snd_seq_client *client,
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(! snd_seq_write_pool_allocated(client) ||
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info->output_pool != client->pool->size)) {
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if (snd_seq_write_pool_allocated(client)) {
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/* is the pool in use? */
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if (atomic_read(&client->pool->counter))
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return -EBUSY;
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/* remove all existing cells */
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snd_seq_pool_mark_closing(client->pool);
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snd_seq_queue_client_leave_cells(client->number);
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