drm/vmwgfx: Potential off by one in vmw_view_add()

BugLink: http://bugs.launchpad.net/bugs/1745266

commit 0d9cac0c upstream.

The vmw_view_cmd_to_type() function returns vmw_view_max (3) on error.
It's one element beyond the end of the vmw_view_cotables[] table.

My read on this is that it's possible to hit this failure.  header->id
comes from vmw_cmd_check() and it's a user controlled number between
1040 and 1225 so we can hit that error.  But I don't have the hardware
to test this code.

Fixes: d80efd5c ("drm/vmwgfx: Initial DX support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -2678,6 +2678,8 @@ static int vmw_cmd_dx_view_define(struct vmw_private *dev_priv,
 	}
 
 	view_type = vmw_view_cmd_to_type(header->id);
+	if (view_type == vmw_view_max)
+		return -EINVAL;
 	cmd = container_of(header, typeof(*cmd), header);
 	ret = vmw_cmd_res_check(dev_priv, sw_context, vmw_res_surface,
 				user_surface_converter,