Commit 5f8cf712 authored Dec 03, 2018 by Hui Peng Committed by Takashi Iwai Dec 03, 2018

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



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: 362e4e49 ("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>

parent 54947cd6

sound/usb/card.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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;

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