[PATCH 3.16 244/366] ALSA: aloop: Add missing cable lock to ctl API callbacks

Ben Hutchings
2018-10-14T23:12:05Z

From: Takashi Iwai <tiwai@suse.de>

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;
}