Patch "ALSA: seq: Fix racy pool initializations" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

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

    ALSA: seq: Fix racy pool initializations

to the 4.9-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-fix-racy-pool-initializations.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d15d662e89fc667b90cd294b0eb45694e33144da Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Mon, 12 Feb 2018 15:20:51 +0100
Subject: ALSA: seq: Fix racy pool initializations
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Content-Transfer-Encoding: 8bit

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
@@ -999,7 +999,7 @@ 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))
@@ -1014,11 +1014,15 @@ 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);


Patches currently in stable-queue which might be from tiwai@suse.de are

queue-4.9/alsa-hda-realtek-pci-quirk-for-fujitsu-u7x7.patch
queue-4.9/alsa-usb-audio-fix-uac2-get_ctl-request-with-a-range-attribute.patch
queue-4.9/alsa-hda-fix-headset-mic-detection-problem-for-two-dell-machines.patch
queue-4.9/alsa-seq-fix-racy-pool-initializations.patch
queue-4.9/alsa-hda-realtek-enable-thinkpad-dock-device-for-alc298-platform.patch
queue-4.9/alsa-usb-audio-add-implicit-fb-quirk-for-behringer-ufx1204.patch