From: Hannes Frederic Sowa <hannes@stressinduktion.org>
To: Werner Almesberger <werner@almesberger.net>
Cc: netdev@vger.kernel.org
Subject: Re: minimum ICMPv6 message size vs. RPL's DIS
Date: Thu, 25 Jul 2013 08:17:31 +0200 [thread overview]
Message-ID: <20130725061731.GA12365@order.stressinduktion.org> (raw)
In-Reply-To: <20130724232852.GA29572@ws>
On Wed, Jul 24, 2013 at 08:28:52PM -0300, Werner Almesberger wrote:
> 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 ?
Browsing the RFCs, I do think you are correct. Did you check what IPv4 does?
(what a strange errata to RFC 4443...)
> 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;
Hmm, maybe we should update the icmp header to something like
struct icmp6hdr {
struct icmp6hdr_head {
__u8 icmp6_type;
...;
} icmpv6_head;
#define icmp6_type icmpv6_head.icmp6_type
and just change the type in icmpv6_filter to icmp6hdr_head.
Hmm, there is a bug in this function, _hdr must not be a pointer.
Greetings,
Hannes
next prev parent reply other threads:[~2013-07-25 6:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-24 23:28 minimum ICMPv6 message size vs. RPL's DIS Werner Almesberger
2013-07-25 6:17 ` Hannes Frederic Sowa [this message]
2013-07-25 10:30 ` Werner Almesberger
2013-07-25 13:03 ` Hannes Frederic Sowa
2013-07-25 13:58 ` Hannes Frederic Sowa
2013-07-25 14:32 ` Werner Almesberger
2013-07-25 18:40 ` Hannes Frederic Sowa
2013-07-25 21:47 ` Werner Almesberger
2013-07-25 23:31 ` Hannes Frederic Sowa
2013-08-01 5:48 ` Hannes Frederic Sowa
2013-08-02 1:10 ` David Miller
2013-08-02 4:51 ` Werner Almesberger
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