From 5f8cf712582617d523120df67d392059eaf2fc4b Mon Sep 17 00:00:00 2001 From: Hui Peng Date: Mon, 3 Dec 2018 16:09:34 +0100 Subject: [PATCH] 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: 362e4e49abe5 ("ALSA: usb-audio - clear chip->probing on error exit") Reported-by: Hui Peng Reported-by: Mathias Payer Signed-off-by: Hui Peng Signed-off-by: Mathias Payer Cc: Signed-off-by: Takashi Iwai --- sound/usb/card.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/sound/usb/card.c b/sound/usb/card.c index 2bfe4e80a6b9..a105947eaf55 100644 --- a/sound/usb/card.c +++ b/sound/usb/card.c @@ -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(®ister_mutex); return err; -- 2.30.2