drm/vmwgfx: Validate the box size for the snooped cursor

Invalid userspace dma surface copies could potentially overflow
the memcpy from the surface to the snooped image leading to crashes.
To fix it the dimensions of the copybox have to be validated
against the expected size of the snooped cursor.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Fixes: 2ac8637 ("vmwgfx: Snoop DMA transfers with non-covering sizes")
Cc: <stable@vger.kernel.org> # v3.2+
Reviewed-by: Michael Banack <banackm@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221026031936.1004280-1-zack@kde.org

drivers/gpu/drm/vmwgfx/vmwgfx_kms.c

@@ -393,7 +393,8 @@ void vmw_kms_cursor_snoop(struct vmw_surface *srf,
 	if (cmd->dma.guest.ptr.offset % PAGE_SIZE ||
 	    box->x != 0    || box->y != 0    || box->z != 0    ||
 	    box->srcx != 0 || box->srcy != 0 || box->srcz != 0 ||
-	    box->d != 1    || box_count != 1) {
+	    box->d != 1    || box_count != 1 ||
+	    box->w > 64 || box->h > 64) {
 		/* TODO handle none page aligned offsets */
 		/* TODO handle more dst & src != 0 */
 		/* TODO handle more then one copy */