From mboxrd@z Thu Jan 1 00:00:00 1970 From: Werner Almesberger Subject: minimum ICMPv6 message size vs. RPL's DIS Date: Wed, 24 Jul 2013 20:28:52 -0300 Message-ID: <20130724232852.GA29572@ws> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: netdev@vger.kernel.org Return-path: Received: from hydra.openmoko.org ([144.76.72.4]:52038 "EHLO hydra.openmoko.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754151Ab3GYARq (ORCPT ); Wed, 24 Jul 2013 20:17:46 -0400 Received: from 201-160-231-201.fibertel.com.ar ([201.231.160.201] helo=ws) by hydra.openmoko.org with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1V28Va-0005JQ-H6 for netdev@vger.kernel.org; Thu, 25 Jul 2013 01:30:15 +0200 Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: The kernel assumes that any valid ICMPv6 message is at least eight bytes long, for example in net/ipv6/raw.c:icmpv6_filter The DIS message of RPL (RFC 6550 section 6.2, from the 6LoWPAN world), has a minimum length of six bytes, and is thus blocked by icmpv6_filter. Contiki OS sends this sort of messages and is thus ignored by an user-space RPL application on Linux (in my case simpleRPL). Nodes will eventually join the network regardless, but this can take hours instead of seconds. RFC 4443 seems to allow even a zero-sized body, making the minimum allowable size four bytes. A similar restriction exists in net/ipv6/icmp.c:icmpv6_rcv but causes no harm there since all potential recipients at that point expect a larger payload. Now, while this is easy enough to fix on the Linux side (see below), I wonder if it is really a Linux bug or if I (and the authors of RPL in Contiki) may have missed some minimum size requirement for ICMPv6 messages stated elsewhere. Opinions ? - Werner diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c index c45f7a5..539534c 100644 --- a/net/ipv6/raw.c +++ b/net/ipv6/raw.c @@ -112,7 +112,7 @@ static int icmpv6_filter(const struct sock *sk, const struct sk_buff *skb) const struct icmp6hdr *hdr; hdr = skb_header_pointer(skb, skb_transport_offset(skb), - sizeof(_hdr), &_hdr); + 4, &_hdr); if (hdr) { const __u32 *data = &raw6_sk(sk)->filter.data[0]; unsigned int type = hdr->icmp6_type;