[34-longterm 163/260] ALSA: prevent heap corruption in snd_ctl_new()

[Paul Gortmaker]

From: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>

commit 5591bf07225523600450edd9e6ad258bb877b779 upstream.

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@xxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 sound/core/control.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 439ce64..85abc46 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 */
@@ -191,6 +192,10 @@ 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");
-- 
1.7.3.3

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