Hi Alistair, Thank you for the patch. On Wednesday, 19 December 2018 03:32:48 EET Alistair Strachan wrote: > From: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx> > Signed-off-by: Alistair Strachan <astrachan@xxxxxxxxxx> > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> > Cc: linux-media@xxxxxxxxxxxxxxx > Cc: kernel-team@xxxxxxxxxxx > --- > 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
