inet_listen_opts: add error checking

Don't use atoi() function which doesn't detect errors, switch to
strtol and error out on failures.  Also add a range check while
being at it.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>

util/qemu-sockets.c

@@ -131,8 +131,19 @@ int inet_listen_opts(QemuOpts *opts, int port_offset, Error **errp)
         ai.ai_family = PF_INET6;
 
     /* lookup */
-    if (port_offset)
-        snprintf(port, sizeof(port), "%d", atoi(port) + port_offset);
+    if (port_offset) {
+        unsigned long long baseport;
+        if (parse_uint_full(port, &baseport, 10) < 0) {
+            error_setg(errp, "can't convert to a number: %s", port);
+            return -1;
+        }
+        if (baseport > 65535 ||
+            baseport + port_offset > 65535) {
+            error_setg(errp, "port %s out of range", port);
+            return -1;
+        }
+        snprintf(port, sizeof(port), "%d", (int)baseport + port_offset);
+    }
     rc = getaddrinfo(strlen(addr) ? addr : NULL, port, &ai, &res);
     if (rc != 0) {
         error_setg(errp, "address resolution failed for %s:%s: %s", addr, port,