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 5.4-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-5.4 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 @@ -800,6 +800,11 @@ 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; @@ -1458,7 +1463,10 @@ 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-5.4/alsa-seq-fix-undefined-behavior-in-bit-shift-for-snd.patch queue-5.4/alsa-hda-hdmi-add-hp-device-0x8711-to-force-connect-list.patch queue-5.4/media-dvb-core-fix-uaf-due-to-refcount-races-at-releasing.patch queue-5.4/alsa-mts64-fix-possible-null-ptr-defer-in-snd_mts64_.patch queue-5.4/alsa-asoc-hda-move-rename-snd_hdac_ext_stop_streams-.patch queue-5.4/alsa-hda-realtek-add-quirk-for-lenovo-tianyi510pro-14iob.patch queue-5.4/alsa-hda-add-snd_hdac_stop_streams-helper.patch queue-5.4/alsa-asihpi-fix-missing-pci_disable_device.patch queue-5.4/alsa-line6-correct-midi-status-byte-when-receiving-data-from-podxt.patch queue-5.4/alsa-pcm-fix-undefined-behavior-in-bit-shift-for-snd.patch queue-5.4/alsa-line6-fix-stack-overflow-in-line6_midi_transmit.patch