media: uvcvideo: Silence shift-out-of-bounds warning

UBSAN reports a shift-out-of-bounds warning in uvc_get_le_value(). The
report is correct, but the issue should be harmless as the computed
value isn't used when the shift is negative. This may however cause
incorrect behaviour if a negative shift could generate adverse side
effects (such as a trap on some architectures for instance).

Regardless of whether that may happen or not, silence the warning as a
full WARN backtrace isn't nice.

Reported-by: Bart Van Assche <bvanassche@acm.org>
Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 76e4c88..f479d89 100644 (file)
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -773,12 +773,16 @@ static s32 uvc_get_le_value(struct uvc_control_mapping *mapping,
        offset &= 7;
        mask = ((1LL << bits) - 1) << offset;
 
-       for (; bits > 0; data++) {
+       while (1) {
                u8 byte = *data & mask;
                value |= offset > 0 ? (byte >> offset) : (byte << (-offset));
                bits -= 8 - (offset > 0 ? offset : 0);
+               if (bits <= 0)
+                       break;
+
                offset -= 8;
                mask = (1 << bits) - 1;
+               data++;
        }
 
        /* Sign-extend the value if needed. */