iptunnel: sanitize copying tunnel name

Since p->name is only IFNAMSIZ bytes, do not copy more than IFNAMSIZ - 1
bytes into it so there remains at least a single null byte in the end.
Signed-off-by: Phil Sutter <phil@nwl.cc>

ip/iptunnel.c

@@ -175,7 +175,7 @@ static int parse_args(int argc, char **argv, int cmd, struct ip_tunnel_parm *p)
 				usage();
 			if (p->name[0])
 				duparg2("name", *argv);
-			strncpy(p->name, *argv, IFNAMSIZ);
+			strncpy(p->name, *argv, IFNAMSIZ - 1);
 			if (cmd == SIOCCHGTUNNEL && count == 0) {
 				struct ip_tunnel_parm old_p;
 				memset(&old_p, 0, sizeof(old_p));