[Lucid][CVE-2014-4656 1/2] ALSA: control: Handle numid overflow

[Luis Henriques]

From: Lars-Peter Clausen <lars at metafoo.de>

Each control gets automatically assigned its numids when the control is created.
The allocation is done by incrementing the numid by the amount of allocated
numids per allocation. This means that excessive creation and destruction of
controls (e.g. via SNDRV_CTL_IOCTL_ELEM_ADD/REMOVE) can cause the id to
eventually overflow. Currently when this happens for the control that caused the
overflow kctl->id.numid + kctl->count will also over flow causing it to be
smaller than kctl->id.numid. Most of the code assumes that this is something
that can not happen, so we need to make sure that it won't happen

Signed-off-by: Lars-Peter Clausen <lars at metafoo.de>
Acked-by: Jaroslav Kysela <perex at perex.cz>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
(cherry picked from commit ac902c112d90a89e59916f751c2745f4dbdbb4bd)
CVE-2014-4656
BugLink: http://bugs.launchpad.net/bugs/1339306
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 sound/core/control.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sound/core/control.c b/sound/core/control.c
index f149a5eab093..acd92ffb2bc2 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -278,6 +278,10 @@ static unsigned int snd_ctl_hole_check(struct snd_card *card,
 {
 	struct snd_kcontrol *kctl;
 
+	/* Make sure that the ids assigned to the control do not wrap around */
+	if (card->last_numid >= UINT_MAX - count)
+		card->last_numid = 0;
+
 	list_for_each_entry(kctl, &card->controls, list) {
 		if ((kctl->id.numid <= card->last_numid &&
 		     kctl->id.numid + kctl->count > card->last_numid) ||
-- 
1.9.1