ALSA: prevent heap corruption in snd_ctl_new()

The snd_ctl_new() function in sound/core/control.c allocates space for a
snd_kcontrol struct by performing arithmetic operations on a
user-provided size without checking for integer overflow.  If a user
provides a large enough size, an overflow will occur, the allocated
chunk will be too small, and a second user-influenced value will be
written repeatedly past the bounds of this chunk.  This code is
reachable by unprivileged users who have permission to open
a /dev/snd/controlC* device (on many distros, this is group "audio") via
the SNDRV_CTL_IOCTL_ELEM_ADD and SNDRV_CTL_IOCTL_ELEM_REPLACE ioctls.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/sound/core/control.c b/sound/core/control.c
index 070aab490191..45a818002d99 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -31,6 +31,7 @@
 
 /* max number of user-defined controls */
 #define MAX_USER_CONTROLS       32
+#define MAX_CONTROL_COUNT       1028
 
 struct snd_kctl_ioctl {
         struct list_head list;          /* list of all ioctls */
@@ -195,6 +196,10 @@ static struct snd_kcontrol *snd_ctl_new(struct snd_kcontrol *control,
         
         if (snd_BUG_ON(!control || !control->count))
                 return NULL;
+
+        if (control->count > MAX_CONTROL_COUNT)
+                return NULL;
+
         kctl = kzalloc(sizeof(*kctl) + sizeof(struct snd_kcontrol_volatile) * control->count, GFP_KERNEL);
         if (kctl == NULL) {
                 snd_printk(KERN_ERR "Cannot allocate control instance\n");