plugins: netlink: slightly stricter ifname validation

Check if ifname contains double periods, this should *not* be a valid
name, though eth0.10 is, et0..10 is not.  Should protect better against
directory traversal attacks.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

plugins/netlink.c

@@ -120,6 +120,9 @@ static int validate_ifname(const char *ifname)
 	if (strlen(ifname) >= IFNAMSIZ)
 		return 1;
 
+	if (strstr(ifname, ".."))
+		return 1;
+
 	while (*ifname) {
 		if (*ifname == '/' || isspace(*ifname))
 			return 1;