[PATCH v2] media: uvcvideo: Fix 'type' check leading to overflow

[PATCH v2] media: uvcvideo: Fix 'type' check leading to overflow

[Alistair Strachan]

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

When initially testing the Camera Terminal Descriptor wTerminalType
field (buffer[4]), no mask is used. Later in the function, the MSB is
overloaded to store the descriptor subtype, and so a mask of 0x7fff
is used to check the type.

If a descriptor is specially crafted to set this overloaded bit in the
original wTerminalType field, the initial type check will fail (falling
through, without adjusting the buffer size), but the later type checks
will pass, assuming the buffer has been made suitably large, causing an
overflow.

Avoid this problem by checking for the MSB in the wTerminalType field.
If the bit is set, assume the descriptor is bad, and abort parsing it.

Originally reported here:
https://groups.google.com/forum/#!topic/syzkaller/Ot1fOE6v1d8
A similar (non-compiling) patch was provided at that time.

Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Alistair Strachan <astrachan@google.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Cc: kernel-team@android.com
---
v2: Use an alternative fix suggested by Laurent
 drivers/media/usb/uvc/uvc_driver.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index bc369a0934a3..7fde3ce642c4 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1065,11 +1065,19 @@ static int uvc_parse_standard_control(struct uvc_device *dev,
 			return -EINVAL;
 		}
 
-		/* Make sure the terminal type MSB is not null, otherwise it
-		 * could be confused with a unit.
+		/*
+		 * Reject invalid terminal types that would cause issues:
+		 *
+		 * - The high byte must be non-zero, otherwise it would be
+		 *   confused with a unit.
+		 *
+		 * - Bit 15 must be 0, as we use it internally as a terminal
+		 *   direction flag.
+		 *
+		 * Other unknown types are accepted.
 		 */
 		type = get_unaligned_le16(&buffer[4]);
-		if ((type & 0xff00) == 0) {
+		if ((type & 0x7f00) == 0 || (type & 0x8000) != 0) {
 			uvc_trace(UVC_TRACE_DESCR, "device %d videocontrol "
 				"interface %d INPUT_TERMINAL %d has invalid "
 				"type 0x%04x, skipping\n", udev->devnum,
-- 
2.20.1.415.g653613c723-goog

Re: [PATCH v2] media: uvcvideo: Fix 'type' check leading to overflow

[Laurent Pinchart]

Hi Alistair,

Thank you for the patch.

On Wednesday, 19 December 2018 03:32:48 EET Alistair Strachan wrote:
> From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Are you sure you don't want to keep authorship ? I've merely reviewed v1 and 
proposed an alternative implementation :-) Let me know what you would prefer 
and I'll apply this to my tree.

> When initially testing the Camera Terminal Descriptor wTerminalType
> field (buffer[4]), no mask is used. Later in the function, the MSB is
> overloaded to store the descriptor subtype, and so a mask of 0x7fff
> is used to check the type.
> 
> If a descriptor is specially crafted to set this overloaded bit in the
> original wTerminalType field, the initial type check will fail (falling
> through, without adjusting the buffer size), but the later type checks
> will pass, assuming the buffer has been made suitably large, causing an
> overflow.
> 
> Avoid this problem by checking for the MSB in the wTerminalType field.
> If the bit is set, assume the descriptor is bad, and abort parsing it.
> 
> Originally reported here:
> https://groups.google.com/forum/#!topic/syzkaller/Ot1fOE6v1d8
> A similar (non-compiling) patch was provided at that time.
> 
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Signed-off-by: Alistair Strachan <astrachan@google.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> Cc: linux-media@vger.kernel.org
> Cc: kernel-team@android.com
> ---
> v2: Use an alternative fix suggested by Laurent
>  drivers/media/usb/uvc/uvc_driver.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c
> b/drivers/media/usb/uvc/uvc_driver.c index bc369a0934a3..7fde3ce642c4
> 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -1065,11 +1065,19 @@ static int uvc_parse_standard_control(struct
> uvc_device *dev, return -EINVAL;
>  		}
> 
> -		/* Make sure the terminal type MSB is not null, otherwise it
> -		 * could be confused with a unit.
> +		/*
> +		 * Reject invalid terminal types that would cause issues:
> +		 *
> +		 * - The high byte must be non-zero, otherwise it would be
> +		 *   confused with a unit.
> +		 *
> +		 * - Bit 15 must be 0, as we use it internally as a terminal
> +		 *   direction flag.
> +		 *
> +		 * Other unknown types are accepted.
>  		 */
>  		type = get_unaligned_le16(&buffer[4]);
> -		if ((type & 0xff00) == 0) {
> +		if ((type & 0x7f00) == 0 || (type & 0x8000) != 0) {
>  			uvc_trace(UVC_TRACE_DESCR, "device %d videocontrol "
>  				"interface %d INPUT_TERMINAL %d has invalid "
>  				"type 0x%04x, skipping\n", udev->devnum,

-- 
Regards,

Laurent Pinchart

Re: [PATCH v2] media: uvcvideo: Fix 'type' check leading to overflow

[Alistair Strachan]

On Wed, Dec 19, 2018 at 12:16 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Alistair,
>
> Thank you for the patch.
>
> On Wednesday, 19 December 2018 03:32:48 EET Alistair Strachan wrote:
> > From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>
> Are you sure you don't want to keep authorship ? I've merely reviewed v1 and
> proposed an alternative implementation :-) Let me know what you would prefer
> and I'll apply this to my tree.

Whatever attribution you think is best works for me! Thank you for
picking up this patch.

> > When initially testing the Camera Terminal Descriptor wTerminalType
> > field (buffer[4]), no mask is used. Later in the function, the MSB is
> > overloaded to store the descriptor subtype, and so a mask of 0x7fff
> > is used to check the type.
> >
> > If a descriptor is specially crafted to set this overloaded bit in the
> > original wTerminalType field, the initial type check will fail (falling
> > through, without adjusting the buffer size), but the later type checks
> > will pass, assuming the buffer has been made suitably large, causing an
> > overflow.
> >
> > Avoid this problem by checking for the MSB in the wTerminalType field.
> > If the bit is set, assume the descriptor is bad, and abort parsing it.
> >
> > Originally reported here:
> > https://groups.google.com/forum/#!topic/syzkaller/Ot1fOE6v1d8
> > A similar (non-compiling) patch was provided at that time.
> >
> > Reported-by: syzbot <syzkaller@googlegroups.com>
> > Signed-off-by: Alistair Strachan <astrachan@google.com>
> > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> > Cc: linux-media@vger.kernel.org
> > Cc: kernel-team@android.com
> > ---
> > v2: Use an alternative fix suggested by Laurent
> >  drivers/media/usb/uvc/uvc_driver.c | 14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c
> > b/drivers/media/usb/uvc/uvc_driver.c index bc369a0934a3..7fde3ce642c4
> > 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -1065,11 +1065,19 @@ static int uvc_parse_standard_control(struct
> > uvc_device *dev, return -EINVAL;
> >               }
> >
> > -             /* Make sure the terminal type MSB is not null, otherwise it
> > -              * could be confused with a unit.
> > +             /*
> > +              * Reject invalid terminal types that would cause issues:
> > +              *
> > +              * - The high byte must be non-zero, otherwise it would be
> > +              *   confused with a unit.
> > +              *
> > +              * - Bit 15 must be 0, as we use it internally as a terminal
> > +              *   direction flag.
> > +              *
> > +              * Other unknown types are accepted.
> >                */
> >               type = get_unaligned_le16(&buffer[4]);
> > -             if ((type & 0xff00) == 0) {
> > +             if ((type & 0x7f00) == 0 || (type & 0x8000) != 0) {
> >                       uvc_trace(UVC_TRACE_DESCR, "device %d videocontrol "
> >                               "interface %d INPUT_TERMINAL %d has invalid "
> >                               "type 0x%04x, skipping\n", udev->devnum,
>
> --
> Regards,
>
> Laurent Pinchart
>
>
>