[PATCH 5.14 039/849] ALSA: mixer: oss: Fix racy access to slots

Greg Kroah-Hartman
2021-11-16T01:46:43Z

From: Takashi Iwai <tiwai@suse.de>

commit 411cef6adfb38a5bb6bd9af3941b28198e7fb680 upstream.

The OSS mixer can reassign the mapping slots dynamically via proc
file. Although the addition and deletion of those slots are protected
by mixer->reg_mutex, the access to slots aren't, hence this may cause
UAF when the slots in use are deleted concurrently.

This patch applies the mixer->reg_mutex in all appropriate code paths
(i.e. the ioctl functions) that may access slots.

Reported-by: syzbot+9988f17cf72a1045a189@syzkaller.appspotmail.com
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000036adc005ceca9175@google.com
Link: https://lore.kernel.org/r/20211020164846.922-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/core/oss/mixer_oss.c | 44 +++++++++++++++++++++++++++++++++-----------
1 file changed, 33 insertions(+), 11 deletions(-)

--- a/sound/core/oss/mixer_oss.c
+++ b/sound/core/oss/mixer_oss.c
@@ -130,11 +130,13 @@ static int snd_mixer_oss_devmask(struct

if (mixer == NULL)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
for (chn = 0; chn < 31; chn++) {
pslot = &mixer->slots[chn];
if (pslot->put_volume || pslot->put_recsrc)
result |= 1 << chn;
}
+ mutex_unlock(&mixer->reg_mutex);
return result;
}

@@ -146,11 +148,13 @@ static int snd_mixer_oss_stereodevs(stru

if (mixer == NULL)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
for (chn = 0; chn < 31; chn++) {
pslot = &mixer->slots[chn];
if (pslot->put_volume && pslot->stereo)
result |= 1 << chn;
}
+ mutex_unlock(&mixer->reg_mutex);
return result;
}

@@ -161,6 +165,7 @@ static int snd_mixer_oss_recmask(struct

if (mixer == NULL)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
if (mixer->put_recsrc && mixer->get_recsrc) { /* exclusive */
result = mixer->mask_recsrc;
} else {
@@ -172,6 +177,7 @@ static int snd_mixer_oss_recmask(struct
result |= 1 << chn;
}
}
+ mutex_unlock(&mixer->reg_mutex);
return result;
}

@@ -182,12 +188,12 @@ static int snd_mixer_oss_get_recsrc(stru

if (mixer == NULL)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
if (mixer->put_recsrc && mixer->get_recsrc) { /* exclusive */
- int err;
unsigned int index;
- err = mixer->get_recsrc(fmixer, &index);
- if (err < 0)
- return err;
+ result = mixer->get_recsrc(fmixer, &index);
+ if (result < 0)
+ goto unlock;
result = 1 << index;
} else {
struct snd_mixer_oss_slot *pslot;
@@ -202,7 +208,10 @@ static int snd_mixer_oss_get_recsrc(stru
}
}
}
- return mixer->oss_recsrc = result;
+ mixer->oss_recsrc = result;
+ unlock:
+ mutex_unlock(&mixer->reg_mutex);
+ return result;
}

static int snd_mixer_oss_set_recsrc(struct snd_mixer_oss_file *fmixer, int recsrc)
@@ -215,6 +224,7 @@ static int snd_mixer_oss_set_recsrc(stru

if (mixer == NULL)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
if (mixer->get_recsrc && mixer->put_recsrc) { /* exclusive input */
if (recsrc & ~mixer->oss_recsrc)
recsrc &= ~mixer->oss_recsrc;
@@ -240,6 +250,7 @@ static int snd_mixer_oss_set_recsrc(stru
}
}
}
+ mutex_unlock(&mixer->reg_mutex);
return result;
}

@@ -251,6 +262,7 @@ static int snd_mixer_oss_get_volume(stru

if (mixer == NULL || slot > 30)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
pslot = &mixer->slots[slot];
left = pslot->volume[0];
right = pslot->volume[1];
@@ -258,15 +270,21 @@ static int snd_mixer_oss_get_volume(stru
result = pslot->get_volume(fmixer, pslot, &left, &right);
if (!pslot->stereo)
right = left;
- if (snd_BUG_ON(left < 0 || left > 100))
- return -EIO;
- if (snd_BUG_ON(right < 0 || right > 100))
- return -EIO;
+ if (snd_BUG_ON(left < 0 || left > 100)) {
+ result = -EIO;
+ goto unlock;
+ }
+ if (snd_BUG_ON(right < 0 || right > 100)) {
+ result = -EIO;
+ goto unlock;
+ }
if (result >= 0) {
pslot->volume[0] = left;
pslot->volume[1] = right;
result = (left & 0xff) | ((right & 0xff) << 8);
}
+ unlock:
+ mutex_unlock(&mixer->reg_mutex);
return result;
}

@@ -279,6 +297,7 @@ static int snd_mixer_oss_set_volume(stru

if (mixer == NULL || slot > 30)
return -EIO;
+ mutex_lock(&mixer->reg_mutex);
pslot = &mixer->slots[slot];
if (left > 100)
left = 100;
@@ -289,10 +308,13 @@ static int snd_mixer_oss_set_volume(stru
if (pslot->put_volume)
result = pslot->put_volume(fmixer, pslot, left, right);
if (result < 0)
- return result;
+ goto unlock;
pslot->volume[0] = left;
pslot->volume[1] = right;
- return (left & 0xff) | ((right & 0xff) << 8);
+ result = (left & 0xff) | ((right & 0xff) << 8);
+ unlock:
+ mutex_lock(&mixer->reg_mutex);
+ return result;
}

static int snd_mixer_oss_ioctl1(struct snd_mixer_oss_file *fmixer, unsigned int cmd, unsigned long arg)