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media: usbtv: prevent access to free'd resources

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commit 2a00932f08 upstream.

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: [<ffffffff81093850>] process_one_work+0x30/0x480
 PGD 405bbf067 PUD 405bbe067 PMD 0
 Call Trace:
  [<ffffffff81093ce8>] worker_thread+0x48/0x4e0
  [<ffffffff81093ca0>] ? process_one_work+0x480/0x480
  [<ffffffff81093ca0>] ? process_one_work+0x480/0x480
  [<ffffffff81099998>] kthread+0xd8/0xf0
  [<ffffffff815c73c2>] ret_from_fork+0x22/0x40
  [<ffffffff810998c0>] ? kthread_worker_fn+0x170/0x170
 ---[ end trace 0f3dac5c1a38e610 ]---

Signed-off-by: Matthew Leach <matthew@mattleach.net>
Tested-by: Peter Sutton <foxxy@foxdogstudios.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Matthew Leach
2016-07-08 09:04:27 -03:00
committed by Greg Kroah-Hartman
parent 43ef3b6969
commit ddc35199f2
1 changed files with 5 additions and 0 deletions
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5
drivers/media/usb/usbtv/usbtv-audio.c
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@@ -278,6 +278,9 @@ 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
@@ -378,6 +381,8 @@ 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;