[SRU,B/C] ALSA: usb-audio: Fix UAF decrement if card has no live interfaces in card.c
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Message ID 20190218144958.7217-2-hui.wang@canonical.com
State New
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Series
  • [SRU,B/C] ALSA: usb-audio: Fix UAF decrement if card has no live interfaces in card.c
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Commit Message

Hui Wang Feb. 18, 2019, 2:49 p.m. UTC
From: Hui Peng <benquike@gmail.com>

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>

CVE-2018-19824

(cherry picked from commit 5f8cf712582617d523120df67d392059eaf2fc4b)
Signed-off-by: Hui Wang <hui.wang@canonical.com>
---
 sound/usb/card.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Tyler Hicks Feb. 18, 2019, 3:31 p.m. UTC | #1
On 2019-02-18 22:49:57, Hui Wang wrote:
> From: Hui Peng <benquike@gmail.com>
> 
> 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>
> 
> CVE-2018-19824
> 
> (cherry picked from commit 5f8cf712582617d523120df67d392059eaf2fc4b)
> Signed-off-by: Hui Wang <hui.wang@canonical.com>

This is a low risk change that cherry picks cleanly.

Acked-by: Tyler Hicks <tyhicks@canonical.com>

Thanks for working on this!

Tyler

> ---
>  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 3ffb8e5aa50c..9ba2dcc0a326 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -672,9 +672,12 @@ 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;
> -- 
> 2.17.1
> 
> 
> -- 
> kernel-team mailing list
> kernel-team@lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
Thadeu Lima de Souza Cascardo Feb. 22, 2019, 8:03 a.m. UTC | #2
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Stefan Bader March 1, 2019, 2:01 p.m. UTC | #3
On 18.02.19 15:49, Hui Wang wrote:
> From: Hui Peng <benquike@gmail.com>
> 
> 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>
> 
> CVE-2018-19824
> 
> (cherry picked from commit 5f8cf712582617d523120df67d392059eaf2fc4b)
> Signed-off-by: Hui Wang <hui.wang@canonical.com>
> ---

Applied to bionic,cosmic/master-next. Thanks.

-Stefan

>  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 3ffb8e5aa50c..9ba2dcc0a326 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -672,9 +672,12 @@ 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;
>

Patch
diff mbox series

diff --git a/sound/usb/card.c b/sound/usb/card.c
index 3ffb8e5aa50c..9ba2dcc0a326 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -672,9 +672,12 @@  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;