Patch "ALSA: seq: Don't allow resizing pool in use" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: seq: Don't allow resizing pool in use

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alsa-seq-don-t-allow-resizing-pool-in-use.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Takashi Iwai <[email protected]>
Date: Mon, 5 Mar 2018 22:00:55 +0100
Subject: ALSA: seq: Don't allow resizing pool in use
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From: Takashi Iwai <[email protected]>

commit d85739367c6d56e475c281945c68fdb05ca74b4c upstream.

This is a fix for a (sort of) fallout in the recent commit d15d662e89fc ("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.

---
 sound/core/seq/seq_clientmgr.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -1838,6 +1838,9 @@ static int snd_seq_ioctl_set_client_pool
 	    (! snd_seq_write_pool_allocated(client) ||
 	     info->output_pool != client->pool->size)) {
 		if (snd_seq_write_pool_allocated(client)) {
+			/* is the pool in use? */
+			if (atomic_read(&client->pool->counter))
+				return -EBUSY;
 			/* remove all existing cells */
 			snd_seq_pool_mark_closing(client->pool);
 			snd_seq_queue_client_leave_cells(client->number);

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/alsa-seq-don-t-allow-resizing-pool-in-use.patch queue-4.15/documentation-sphinx-fix-directive-import-error.patch queue-4.15/alsa-hda-add-dock-and-led-support-for-hp-probook-640-g2.patch queue-4.15/alsa-hda-realtek-make-dock-sound-work-on-thinkpad-l570.patch queue-4.15/alsa-hda-realtek-limit-mic-boost-on-t480.patch queue-4.15/alsa-hda-add-dock-and-led-support-for-hp-elitebook-820-g3.patch queue-4.15/alsa-seq-more-protection-for-concurrent-write-and-ioctl-races.patch queue-4.15/alsa-hda-realtek-add-support-headset-mode-for-dell-wyse.patch queue-4.15/alsa-hda-realtek-add-headset-mode-support-for-dell-laptop.patch queue-4.15/alsa-hda-fix-a-wrong-fixup-for-alc289-on-dell-machines.patch queue-4.15/alsa-hda-realtek-fix-dock-line-out-volume-on-dell-precision-7520.patch