This is a note to let you know that I've just added the patch titled
media: dvb-core: Fix UAF due to refcount races at releasing
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
media-dvb-core-fix-uaf-due-to-refcount-races-at-releasing.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From fd3d91ab1c6ab0628fe642dd570b56302c30a792 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@xxxxxxx>
Date: Mon, 31 Oct 2022 11:02:45 +0100
Subject: media: dvb-core: Fix UAF due to refcount races at releasing
From: Takashi Iwai <tiwai@xxxxxxx>
commit fd3d91ab1c6ab0628fe642dd570b56302c30a792 upstream.
The dvb-core tries to sync the releases of opened files at
dvb_dmxdev_release() with two refcounts: dvbdev->users and
dvr_dvbdev->users. A problem is present in those two syncs: when yet
another dvb_demux_open() is called during those sync waits,
dvb_demux_open() continues to process even if the device is being
closed. This includes the increment of the former refcount, resulting
in the leftover refcount after the sync of the latter refcount at
dvb_dmxdev_release(). It ends up with use-after-free, since the
function believes that all usages were gone and releases the
resources.
This patch addresses the problem by adding the check of dmxdev->exit
flag at dvb_demux_open(), just like dvb_dvr_open() already does. With
the exit flag check, the second call of dvb_demux_open() fails, hence
the further corruption can be avoided.
Also for avoiding the races of the dmxdev->exit flag reference, this
patch serializes the dmxdev->exit set up and the sync waits with the
dmxdev->mutex lock at dvb_dmxdev_release(). Without the mutex lock,
dvb_demux_open() (or dvb_dvr_open()) may run concurrently with
dvb_dmxdev_release(), which allows to skip the exit flag check and
continue the open process that is being closed.
CVE-2022-41218 is assigned to those bugs above.
Reported-by: Hyunwoo Kim <imv4bel@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/20220908132754.30532-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/media/dvb-core/dmxdev.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -738,6 +738,11 @@ static int dvb_demux_open(struct inode *
if (mutex_lock_interruptible(&dmxdev->mutex))
return -ERESTARTSYS;
+ if (dmxdev->exit) {
+ mutex_unlock(&dmxdev->mutex);
+ return -ENODEV;
+ }
+
for (i = 0; i < dmxdev->filternum; i++)
if (dmxdev->filter[i].state == DMXDEV_STATE_FREE)
break;
@@ -1253,7 +1258,10 @@ EXPORT_SYMBOL(dvb_dmxdev_init);
void dvb_dmxdev_release(struct dmxdev *dmxdev)
{
+ mutex_lock(&dmxdev->mutex);
dmxdev->exit = 1;
+ mutex_unlock(&dmxdev->mutex);
+
if (dmxdev->dvbdev->users > 1) {
wait_event(dmxdev->dvbdev->wait_queue,
dmxdev->dvbdev->users == 1);
Patches currently in stable-queue which might be from tiwai@xxxxxxx are
queue-4.14/alsa-seq-fix-undefined-behavior-in-bit-shift-for-snd.patch
queue-4.14/media-dvb-core-fix-uaf-due-to-refcount-races-at-releasing.patch
queue-4.14/alsa-mts64-fix-possible-null-ptr-defer-in-snd_mts64_.patch
queue-4.14/alsa-asihpi-fix-missing-pci_disable_device.patch
queue-4.14/alsa-line6-correct-midi-status-byte-when-receiving-data-from-podxt.patch
queue-4.14/alsa-line6-fix-stack-overflow-in-line6_midi_transmit.patch
