Hello, On Tue, Aug 18, 2020 at 02:58:22PM -0300, Fabio Estevam wrote: > Hi Bart/Laurent, > > On Tue, Aug 18, 2020 at 2:41 PM Bart Van Assche <bvanassche@xxxxxxx> wrote: > > > > Hi, > > > > This morning I installed a debug build of kernel v5.8.1 on my laptop. > > The complaint shown below appeared in the kernel log. Is this a known > > issue? > > > > ================================================================================ > > UBSAN: shift-out-of-bounds in drivers/media/usb/uvc/uvc_ctrl.c:781:13 > > shift exponent -7 is negative > > Should we fix it like this? > > --- a/drivers/media/usb/uvc/uvc_ctrl.c > +++ b/drivers/media/usb/uvc/uvc_ctrl.c > @@ -778,7 +778,7 @@ static s32 uvc_get_le_value(struct > uvc_control_mapping *mapping, > value |= offset > 0 ? (byte >> offset) : (byte << (-offset)); > bits -= 8 - (offset > 0 ? offset : 0); > offset -= 8; > - mask = (1 << bits) - 1; > + mask = (1LL << bits) - 1; > } No, the issue is that bits is equal to -7, 1LL won't change that. Once bits become negative, the loop stops, and the mask value isn't used afterwards. This would only cause an issue if a shift with a negative value generated side effects (such as a trap for instance) on top of producing an incorrect result. Can this happen ? I suppose we should silence the warning even if it's a false positive, as it doesn't look good in the kernel log. -- Regards, Laurent Pinchart
