releases/3.16.60/alsa-aloop-add-missing-cable-lock-to-ctl-api-callbacks.patch

From: Takashi Iwai <tiwai@suse.de>
Date: Mon, 30 Apr 2018 10:06:48 +0200
Subject: ALSA: aloop: Add missing cable lock to ctl API callbacks

commit 76b3421b39bd610546931fc923edcf90c18fa395 upstream.

Some control API callbacks in aloop driver are too lazy to take the
loopback->cable_lock and it results in possible races of cable access
while it's being freed.  It eventually lead to a UAF, as reported by
fuzzer recently.

This patch covers such control API callbacks and add the proper mutex
locks.

Reported-by: DaeRyong Jeong <threeearcat@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 sound/drivers/aloop.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -829,9 +829,11 @@ static int loopback_rate_shift_get(struc
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
+	mutex_lock(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].rate_shift;
+	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }
 
@@ -863,9 +865,11 @@ static int loopback_notify_get(struct sn
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
+	mutex_lock(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].notify;
+	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }
 
@@ -877,12 +881,14 @@ static int loopback_notify_put(struct sn
 	int change = 0;
 
 	val = ucontrol->value.integer.value[0] ? 1 : 0;
+	mutex_lock(&loopback->cable_lock);
 	if (val != loopback->setup[kcontrol->id.subdevice]
 				[kcontrol->id.device].notify) {
 		loopback->setup[kcontrol->id.subdevice]
 			[kcontrol->id.device].notify = val;
 		change = 1;
 	}
+	mutex_unlock(&loopback->cable_lock);
 	return change;
 }
 
@@ -890,13 +896,16 @@ static int loopback_active_get(struct sn
 			       struct snd_ctl_elem_value *ucontrol)
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
-	struct loopback_cable *cable = loopback->cables
-			[kcontrol->id.subdevice][kcontrol->id.device ^ 1];
+	struct loopback_cable *cable;
+
 	unsigned int val = 0;
 
+	mutex_lock(&loopback->cable_lock);
+	cable = loopback->cables[kcontrol->id.subdevice][kcontrol->id.device ^ 1];
 	if (cable != NULL)
 		val = (cable->running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) ?
 									1 : 0;
+	mutex_unlock(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] = val;
 	return 0;
 }
@@ -939,9 +948,11 @@ static int loopback_rate_get(struct snd_
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
+	mutex_lock(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].rate;
+	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }
 
@@ -961,9 +972,11 @@ static int loopback_channels_get(struct
 {
 	struct loopback *loopback = snd_kcontrol_chip(kcontrol);
 	
+	mutex_lock(&loopback->cable_lock);
 	ucontrol->value.integer.value[0] =
 		loopback->setup[kcontrol->id.subdevice]
 			       [kcontrol->id.device].channels;
+	mutex_unlock(&loopback->cable_lock);
 	return 0;
 }