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ALSA: usb-audio: Fix UAF decrement if card has no live interfaces in card.c

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If a USB sound card reports 0 interfaces, an error condition is triggered
and the function usb_audio_probe errors out. In the error path, there was a
use-after-free vulnerability where the memory object of the card was first
freed, followed by a decrement of the number of active chips. Moving the
decrement above the atomic_dec fixes the UAF.

[ The original problem was introduced in 3.1 kernel, while it was
  developed in a different form.  The Fixes tag below indicates the
  original commit but it doesn't mean that the patch is applicable
  cleanly. -- tiwai ]

Fixes: 362e4e49ab ("ALSA: usb-audio - clear chip->probing on error exit")
Reported-by: Hui Peng <benquike@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Signed-off-by: Hui Peng <benquike@gmail.com>
Signed-off-by: Mathias Payer <mathias.payer@nebelwelt.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Hui Peng 2018-12-03 16:09:34 +01:00 committed by Takashi Iwai
parent 54947cd64c
commit 5f8cf71258
1 changed files with 4 additions and 1 deletions
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5
sound/usb/card.c
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@ -682,9 +682,12 @@ static int usb_audio_probe(struct usb_interface *intf,
__error:
if (chip) {
/* chip->active is inside the chip->card object,
* decrement before memory is possibly returned.
*/
atomic_dec(&chip->active);
if (!chip->num_interfaces)
snd_card_free(chip->card);
atomic_dec(&chip->active);
}
mutex_unlock(&register_mutex);
return err;