[PATCH v2] fbdev: Detect integer underflow at "struct fbcon_ops"->clear_margins.

[Tetsuo Handa]

On 2020/07/16 0:12, Dan Carpenter wrote:
> I've complained about integer overflows in fbdev for a long time...
> 
> What I'd like to see is something like the following maybe.  I don't
> know how to get the vc_data in fbmem.c so it doesn't include your checks
> for negative.

Yes. Like I said "Thus, I consider that we need more sanity/constraints checks." at
https://lore.kernel.org/lkml/b1e7dd6a-fc22-bba8-0abb-d3e779329bce@i-love.sakura.ne.jp/ ,
we want basic checks. That's a task for fbdev people who should be familiar with
necessary constraints.

Anyway, my two patches are small and low cost; can we apply these patches regardless
of basic checks?