Re: [Linux-fbdev-devel] [linux-fbdev-devel][PATCH]fb_pan_display:add x/yoffset check

[Kai J. <b1...@fr...>]

Florian Tobias Schandinat wrote:
> Ville Syrjälä schrieb:
>>> So here we have to check the whether the x/yoffset is smaller than 
>>> zero. If the offset is smaller than zero, in the driver, we should 
>>> not move the virtual screen any more.
>>
>> Checking for overflow will catch you buggy application's negative
>> values too.
>
> That's true, but the problem lies in the current implementation first 
> adding the resolution, which results in small negative [0 to 
> -resolution] values (=large positives) being accepted as they overflow 
> during add and become small positive values.
> I'd recommend changing
>
> var->yoffset + yres > info->var.yres_virtual ||
> var->xoffset + info->var.xres > info->var.xres_virtual
>
> to
>
> var->yoffset > info->var.yres_virtual - yres ||
> var->xoffset > info->var.xres_virtual - info->var.xres
>
I am not sure why do we have these change. Could you give a detail 
description or an example?
Thanks!

Best Regards,

Kai Jiang