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

[Luis Henriques]

On Tue, Apr 16, 2013 at 01:40:44PM +0100, Andy Whitcroft wrote:
> 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.

Well, it really doesn't make a difference.  I just though it would be
better to track upstream.  This way we can eventually add other
definitions in between and keep using the same values.

>
> >  #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.

Heh, I found that amusing as well.

>
> >  	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

Cheers,
--
Luis