From 2a00932f082aff93c3a55426e0c7af6d0ec03997 Mon Sep 17 00:00:00 2001 From: Matthew Leach Date: Fri, 8 Jul 2016 09:04:27 -0300 Subject: [media] media: usbtv: prevent access to free'd resources When disconnecting the usbtv device, the sound card is unregistered from ALSA and the snd member of the usbtv struct is set to NULL. If the usbtv snd_trigger work is running, this can cause a race condition where the kernel will attempt to access free'd resources, shown in [1]. This patch fixes the disconnection code by cancelling any snd_trigger work before unregistering the sound card from ALSA and checking that the snd member still exists in the work function. [1]: usb 3-1.2: USB disconnect, device number 6 BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [] process_one_work+0x30/0x480 PGD 405bbf067 PUD 405bbe067 PMD 0 Call Trace: [] worker_thread+0x48/0x4e0 [] ? process_one_work+0x480/0x480 [] ? process_one_work+0x480/0x480 [] kthread+0xd8/0xf0 [] ret_from_fork+0x22/0x40 [] ? kthread_worker_fn+0x170/0x170 ---[ end trace 0f3dac5c1a38e610 ]--- Signed-off-by: Matthew Leach Tested-by: Peter Sutton Cc: stable@vger.kernel.org Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab --- drivers/media/usb/usbtv/usbtv-audio.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'drivers/media/usb') diff --git a/drivers/media/usb/usbtv/usbtv-audio.c b/drivers/media/usb/usbtv/usbtv-audio.c index d4b4db302f96..1965ff1b1f12 100644 --- a/drivers/media/usb/usbtv/usbtv-audio.c +++ b/drivers/media/usb/usbtv/usbtv-audio.c @@ -292,6 +292,9 @@ static void snd_usbtv_trigger(struct work_struct *work) { struct usbtv *chip = container_of(work, struct usbtv, snd_trigger); + if (!chip->snd) + return; + if (atomic_read(&chip->snd_stream)) usbtv_audio_start(chip); else @@ -392,6 +395,8 @@ err: void usbtv_audio_free(struct usbtv *usbtv) { + cancel_work_sync(&usbtv->snd_trigger); + if (usbtv->snd && usbtv->udev) { snd_card_free(usbtv->snd); usbtv->snd = NULL; -- cgit v1.2.3-59-g8ed1b