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

[Florian T. S. <Flo...@gm...>]

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


Greetings,

Florian Tobias Schandinat