Commit 2a00932f authored by Matthew Leach's avatar Matthew Leach Committed by Mauro Carvalho Chehab

[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: default avatarMatthew Leach <matthew@mattleach.net>
Tested-by: default avatarPeter Sutton <foxxy@foxdogstudios.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent f6399833
...@@ -292,6 +292,9 @@ static void snd_usbtv_trigger(struct work_struct *work) ...@@ -292,6 +292,9 @@ static void snd_usbtv_trigger(struct work_struct *work)
{ {
struct usbtv *chip = container_of(work, struct usbtv, snd_trigger); struct usbtv *chip = container_of(work, struct usbtv, snd_trigger);
if (!chip->snd)
return;
if (atomic_read(&chip->snd_stream)) if (atomic_read(&chip->snd_stream))
usbtv_audio_start(chip); usbtv_audio_start(chip);
else else
...@@ -392,6 +395,8 @@ int usbtv_audio_init(struct usbtv *usbtv) ...@@ -392,6 +395,8 @@ int usbtv_audio_init(struct usbtv *usbtv)
void usbtv_audio_free(struct usbtv *usbtv) void usbtv_audio_free(struct usbtv *usbtv)
{ {
cancel_work_sync(&usbtv->snd_trigger);
if (usbtv->snd && usbtv->udev) { if (usbtv->snd && usbtv->udev) {
snd_card_free(usbtv->snd); snd_card_free(usbtv->snd);
usbtv->snd = NULL; usbtv->snd = NULL;
......
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