Re: [Intel-gfx] [PATCH 3/3] drm/fb-helper: fix input validation gaps in check_var

[Javier Martinez Canillas <javierm@redhat.com>]

Daniel Vetter <daniel@ffwll.ch> writes:

[...]

>> 
>> but only the 'var->xres > fb->width || var->yres > fb->height' from the
>> conditions checked could be false after your __fill_var() call above.
>> 
>> You should drop the 'var->bits_per_pixel > bpp', 'var->xres_virtual >
>> fb->width' and 'var->yres_virtual > fb->height' checks I believe since
>> those will always be true.
>
> The __fill_var is after this. I'm honestly not sure what the exact

Ah, your patch adds it after that indeed. Please ignore my comment then.

> semantics are supposed to be, but essentially if userspace asks for too
> big virtual size, we reject it. And for anything else we then tell it
> (with __fill_var) how big the actually available space is.
>
> What I'm wondering now is whether too small x/yres won't lead to problems
> of some sorts ... For multi-screen we set the virtual size to be big
> enough for all crtc, and then just set x/yres to be the smallest output.
> That way fbcon knows to only draw as much as is visible on all screens.
> But if you then pan that too much, the bigger screens might not have a big
> enough buffer anymore and things fail (but shouldn't).
>
> Not sure how to fix that tbh.

Would this be a problem in practice?

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat