Re: Suggest make 'user_access_begin()' do 'access_ok()' to stable kernel

[Miles Chen <miles.chen@mediatek.com>]

On Thu, 2020-06-11 at 13:15 +0200, Greg KH wrote:
> On Thu, Jun 11, 2020 at 09:37:42AM +0800, Miles Chen wrote:
> > @@ -2601,7 +2603,17 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
> >  		unsigned int i;
> >  
> >  		/* Copy the new buffer offsets back to the user's exec list. */
> > -		user_access_begin();
> > +		/*
> > +		 * Note: count * sizeof(*user_exec_list) does not overflow,
> > +		 * because we checked 'count' in check_buffer_count().
> > +		 *
> > +		 * And this range already got effectively checked earlier
> > +		 * when we did the "copy_from_user()" above.
> > +		 */
> > +		if (!user_access_begin(VERIFY_WRITE, user_exec_list,
> > +				       count * sizeof(*user_exec_list)))
> > +			goto end_user;
> > +
> >  		for (i = 0; i < args->buffer_count; i++) {
> >  			if (!(exec2_list[i].offset & UPDATE))
> >  				continue;
> 
> No one seems to have test-built this code, it fails here on the 4.14.y
> kernel  :(
> 
> I'll go fix it up, but please, always at the very least, test build your
> patches before sending them out...
> 
> thanks,

Sorry for the breakage. It won't happen next time.

cheers,
Miles

> 
> greg k-h