4.4-stable review patch. If anyone has any objections, please let me know.
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From: Hui Peng benquike@gmail.com
commit 5f8cf712582617d523120df67d392059eaf2fc4b upstream.
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: 362e4e49abe5 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- sound/usb/card.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/sound/usb/card.c +++ b/sound/usb/card.c @@ -589,9 +589,12 @@ static int usb_audio_probe(struct usb_in
__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(®ister_mutex); return err;