drm/vmwgfx: NULL pointer dereference from vmw_cmd_dx_view_define()

If SVGA_3D_CMD_DX_DEFINE_RENDERTARGET_VIEW is called with a surface
ID of SVGA3D_INVALID_ID, the srf struct will remain NULL after
vmw_cmd_res_check(), leading to a null pointer dereference in
vmw_view_add().

Cc: <stable@vger.kernel.org>
Fixes: d80efd5 ("drm/vmwgfx: Initial DX support")
Signed-off-by: Murray McAllister <murray.mcallister@gmail.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -2427,6 +2427,10 @@ static int vmw_cmd_dx_view_define(struct vmw_private *dev_priv,
 		return -EINVAL;
 
 	cmd = container_of(header, typeof(*cmd), header);
+	if (unlikely(cmd->sid == SVGA3D_INVALID_ID)) {
+		VMW_DEBUG_USER("Invalid surface id.\n");
+		return -EINVAL;
+	}
 	ret = vmw_cmd_res_check(dev_priv, sw_context, vmw_res_surface,
 				VMW_RES_DIRTY_NONE, user_surface_converter,
 				&cmd->sid, &srf);