[media] media: usbtv: prevent access to free'd resources
authorMatthew Leach <matthew@mattleach.net>
Fri, 8 Jul 2016 12:04:27 +0000 (09:04 -0300)
committerMauro Carvalho Chehab <mchehab@s-opensource.com>
Tue, 12 Jul 2016 16:31:08 +0000 (13:31 -0300)
commit2a00932f082aff93c3a55426e0c7af6d0ec03997
tree6dcc3eb1db8af83294f56da84e4f73d989f531d2
parentf63998331935821071f0b1b4d20bcdb80ca4cc56
[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: [<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>
Cc: stable@vger.kernel.org
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
drivers/media/usb/usbtv/usbtv-audio.c