On Fri, Mar 15, 2013 at 09:36:07AM -0700, Ben Widawsky wrote: > On Fri, Mar 15, 2013 at 08:24:03AM +0000, Chris Wilson wrote: > > That's what I thought too. Looking at the stack trace, the empirical > > evidence is that we need the check. > > -Chris > > I think we need to investigate the issue more then, or put a BUG_ON() in > the drm code and run it through trinity. We have other places where arg > can't/shouldn't be NULL and we don't check. Actually we are both wrong. drm_ioctl() does not validate that the user struct matches the expected size, just ensures that if that user cmd specifies that the arg is to be used that it only up to the known size is copied. A hostile userspace can bludgen a NULL pointer through drm_ioctl() into the driver->ioctl->func(). If we used driver->ioctl->cmd instead of the user supplied cmd, we would have a whole other can of worms to deal with (as we suddenly get a struct of zeroes). However, those worms should already be treated as invalid. Choose your poison. -Chris -- Chris Wilson, Intel Open Source Technology Centre
