Hi Johan,

On Tue, Oct 26, 2021 at 02:06:55PM +0200, Johan Hovold wrote:

On Tue, Oct 26, 2021 at 02:15:20PM +0300, Laurent Pinchart wrote:

quoted

On Tue, Oct 26, 2021 at 11:55:05AM +0100, Kieran Bingham wrote:

quoted

Quoting Johan Hovold (2021-10-26 10:55:11)

quoted

Add the missing bulk-endpoint max-packet sanity check to probe() to
avoid division by zero in uvc_alloc_urb_buffers() in case a malicious
device has broken descriptors (or when doing descriptor fuzz testing).

Note that USB core will reject URBs submitted for endpoints with zero
wMaxPacketSize but that drivers doing packet-size calculations still
need to handle this (cf. commit 2548288b4fb0 ("USB: Fix: Don't skip
endpoint descriptors with maxpacket=0")).

Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
Cc: stable@vger.kernel.org      # 2.6.26
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/media/usb/uvc/uvc_video.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index e16464606b14..85ac5c1081b6 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c

@@ -1958,6 +1958,10 @@ static int uvc_video_start_transfer(struct uvc_streaming *stream,
                if (ep == NULL)
                        return -EIO;
 
+               /* Reject broken descriptors. */
+               if (usb_endpoint_maxp(&ep->desc) == 0)
+                       return -EIO;

Is there any value in identifying this with a specific return code like
-ENODATA?

Going one step further, wouldn't it be better to fail probe() for those
devices ?

This is not how the driver works today. Look at the "return -EIO" just
above in case the expected endpoint is missing. And similarly for the
isochronous case for which zero wMaxPacket isn't handled until
uvc_video_start_transfer() either (a few lines further up still).

That's a good point, it wouldn't be reasonable to ask you to fix all
that :-)

Note however the copy-paste error in the commit message mentioning
probe(), which is indeed where this would typically be handled.

Do you want me to resend or can you change

	s/probe()/uvc_video_start_transfer()/

in the commit message when applying if you think this is acceptable as
is?

I can fix this when applying.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

-- 
Regards,

Laurent Pinchart