On Wed, Dec 19, 2018 at 12:16 AM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> 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@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. 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@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 > > >
