Re: [PATCH v3 23/23] drm/qxl: add overflow checks to qxl_mode_dumb_create()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Jan 18, 2019 at 04:49:44PM +0100, Daniel Vetter wrote:
> On Fri, Jan 18, 2019 at 01:20:20PM +0100, Gerd Hoffmann wrote:
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> 
> We already do all reasonable overflow checks in drm_mode_create_dumb(). If
> you don't trust them I think would be better time spent typing an igt to
> test this than adding redundant check in all drivers.
> 
> You're also missing one check for bpp underflows :-)

BTW I just noticed that we don't seem to validating 
create_dumb->flags at all. Someone should probably add some
checks for that, or mark it as deprecated in case we already
lost the battle with userspace stack garbage.

> -Daniel
> 
> > ---
> >  drivers/gpu/drm/qxl/qxl_dumb.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/qxl/qxl_dumb.c b/drivers/gpu/drm/qxl/qxl_dumb.c
> > index 272d19b677..bed6d06ee4 100644
> > --- a/drivers/gpu/drm/qxl/qxl_dumb.c
> > +++ b/drivers/gpu/drm/qxl/qxl_dumb.c
> > @@ -37,11 +37,13 @@ int qxl_mode_dumb_create(struct drm_file *file_priv,
> >  	uint32_t handle;
> >  	int r;
> >  	struct qxl_surface surf;
> > -	uint32_t pitch, format;
> > +	uint32_t pitch, size, format;
> >  
> > -	pitch = args->width * ((args->bpp + 1) / 8);
> > -	args->size = pitch * args->height;
> > -	args->size = ALIGN(args->size, PAGE_SIZE);
> > +	if (check_mul_overflow(args->width, ((args->bpp + 1) / 8), &pitch))
> > +		return -EINVAL;
> > +	if (check_mul_overflow(pitch, args->height, &size))
> > +		return -EINVAL;
> > +	args->size = ALIGN(size, PAGE_SIZE);
> >  
> >  	switch (args->bpp) {
> >  	case 16:
> > -- 
> > 2.9.3
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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> dri-devel@lists.freedesktop.org
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-- 
Ville Syrjälä
Intel