[Acked/cmt] [Lucid CVE-2013-1860] USB: cdc-wdm: fix buffer overflow

[Andy Whitcroft]

On Tue, Apr 16, 2013 at 12:16:19PM +0100, Luis Henriques wrote:
> From: Oliver Neukum <oneukum at suse.de>
> 
> CVE-2013-1860
> 
> BugLink: http://bugs.launchpad.net/bugs/1156784
> 
> The buffer for responses must not overflow.
> If this would happen, set a flag, drop the data and return
> an error after user space has read all remaining data.
> 
> Signed-off-by: Oliver Neukum <oliver at neukum.org>
> CC: stable at kernel.org
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (back ported from commit c0f5ecee4e741667b2493c742b60b6218d40b3aa)
> 
> Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
> ---
>  drivers/usb/class/cdc-wdm.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
> index 37f2899..6ca1363 100644
> --- a/drivers/usb/class/cdc-wdm.c
> +++ b/drivers/usb/class/cdc-wdm.c
> @@ -52,7 +52,7 @@ MODULE_DEVICE_TABLE (usb, wdm_ids);
>  #define WDM_READ		4
>  #define WDM_INT_STALL		5
>  #define WDM_POLL_RUNNING	6
> -
> +#define WDM_OVERFLOW		10

Odd, but follows upstream allocation.

>  #define WDM_MAX			16
>  
> @@ -115,6 +115,7 @@ static void wdm_in_callback(struct urb *urb)
>  {
>  	struct wdm_device *desc = urb->context;
>  	int status = urb->status;
> +	int length = urb->actual_length;
>  
>  	spin_lock(&desc->iuspin);
>  
> @@ -144,9 +145,17 @@ static void wdm_in_callback(struct urb *urb)
>  	}
>  
>  	desc->rerr = status;
> -	desc->reslength = urb->actual_length;
> -	memmove(desc->ubuf + desc->length, desc->inbuf, desc->reslength);
> -	desc->length += desc->reslength;
> +	if (length + desc->length > desc->wMaxCommand) {
> +		/* The buffer would overflow */
> +		set_bit(WDM_OVERFLOW, &desc->flags);
> +	} else {
> +		/* we may already be in overflow */
> +		if (!test_bit(WDM_OVERFLOW, &desc->flags)) {
> +			memmove(desc->ubuf + desc->length, desc->inbuf, length);
> +			desc->length += length;
> +			desc->reslength = length;
> +		}
> +	}

Why this is not } else if (!test_bit(...)) { I do not know, but it
follows the upstream commit.

>  	wake_up(&desc->wait);
>  
>  	set_bit(WDM_READ, &desc->flags);
> @@ -398,6 +407,11 @@ retry:
>  			rv = -ENODEV;
>  			goto err;
>  		}
> +		if (test_bit(WDM_OVERFLOW, &desc->flags)) {
> +			clear_bit(WDM_OVERFLOW, &desc->flags);
> +			rv = -ENOBUFS;
> +			goto err;
> +		}
>  		i++;
>  		if (file->f_flags & O_NONBLOCK) {
>  			if (!test_bit(WDM_READ, &desc->flags)) {
> @@ -440,6 +454,7 @@ retry:
>  			spin_unlock_irq(&desc->iuspin);
>  			goto retry;
>  		}
> +
>  		if (!desc->reslength) { /* zero length read */
>  			dev_dbg(&desc->intf->dev, "%s: zero length - clearing WDM_READ\n", __func__);
>  			clear_bit(WDM_READ, &desc->flags);
> @@ -844,6 +859,7 @@ static int wdm_post_reset(struct usb_interface *intf)
>  	struct wdm_device *desc = usb_get_intfdata(intf);
>  	int rv;
>  
> +	clear_bit(WDM_OVERFLOW, &desc->flags);
>  	rv = recover_from_urb_loss(desc);
>  	mutex_unlock(&desc->plock);
>  	return 0;

Looks to carry the essentials of the upstream commit to my eye.

Acked-by: Andy Whitcroft <apw at canonical.com>

-apw