viafb: use display information in info not in var for panning

commit d933990c upstream.

As Laurent pointed out we must not use any information in the passed
var besides xoffset, yoffset and vmode as otherwise applications
might abuse it. Also use the aligned fix.line_length and not the
(possible) unaligned xres_virtual.
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/video/via/viafbdev.c

@@ -348,8 +348,9 @@ static int viafb_pan_display(struct fb_var_screeninfo *var,
 	struct fb_info *info)
 {
 	struct viafb_par *viapar = info->par;
-	u32 vram_addr = (var->yoffset * var->xres_virtual + var->xoffset)
-		* (var->bits_per_pixel / 8) + viapar->vram_addr;
+	u32 vram_addr = viapar->vram_addr
+		+ var->yoffset * info->fix.line_length
+		+ var->xoffset * info->var.bits_per_pixel / 8;
 
 	DEBUG_MSG(KERN_DEBUG "viafb_pan_display, address = %d\n", vram_addr);
 	if (!viafb_dual_fb) {