Re: [PATCH 27/44] drivers/tty/vt: use umin() instead of min_t(u16, ...) for row/col limits

[Jiri Slaby]

On 19. 11. 25, 23:41, david.laight.linux@xxxxxxxxx wrote:
> From: David Laight <david.laight.linux@xxxxxxxxx>
>
> The row/column bounds (for a screen window box) are changed from
> 'offset one' to 'offset zero' and bound to the screen size using:
> 	v->xs = min_t(u16, v->xs - 1, vc->vc_cols - 1);
> This has the side effect of converting zero to the limit.
>
> A check I'm adding to min_t() reports that (u16)(v->xs - 1) (etc)
> discards signiticant bits (because v->xs is promoted to 'int' before
> the addition).
> If v->xs is zero (it comes from userspace) it converts -1 to 0xffff.
> This is then bounded to 'vc->vc_cols - 1' which will be fine.
>
> Replace with:
> 	v->xs = umin(v->xs - 1, vc->vc_cols - 1);
> which again converts a -1 to unsigned - this time to 0xffffffff,
> with the same overall effect.

LGTM:

Reviewed-by: Jiri Slaby <jirislaby@xxxxxxxxxx>

> Whether zero is meant to mean the 'maximum size' is unknown.
> I can't find any documentation for the ioctl and it pre-dates git.

Behavior of zero is unspecified AFAICT (the impl can do whatever is easy 
:)).

thanks,
--
js
suse labs