remoteproc: Harden rproc_handle_vdev() against integer overflow

The struct_size() macro protects against integer overflows but adding
"+ rsc->config_len" introduces the risk of integer overflows again.
Use size_add() to be safe.

Fixes: c8784657 ("remoteproc: use struct_size() helper")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Link: https://lore.kernel.org/r/YyMyoPoGOJUcEpZT@kiliSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

drivers/remoteproc/remoteproc_core.c

@@ -520,12 +520,13 @@ static int rproc_handle_vdev(struct rproc *rproc, void *ptr,
 	struct fw_rsc_vdev *rsc = ptr;
 	struct device *dev = &rproc->dev;
 	struct rproc_vdev *rvdev;
+	size_t rsc_size;
 	int i, ret;
 	char name[16];
 
 	/* make sure resource isn't truncated */
-	if (struct_size(rsc, vring, rsc->num_of_vrings) + rsc->config_len >
-			avail) {
+	rsc_size = struct_size(rsc, vring, rsc->num_of_vrings);
+	if (size_add(rsc_size, rsc->config_len) > avail) {
 		dev_err(dev, "vdev rsc is truncated\n");
 		return -EINVAL;
 	}