ipv6: allow to send packet after receiving ICMPv6 Too Big message with MTU field less than IPV6_MIN_MTU
Subsystems (4)
PATCH 1/1 ipv6: allow to send packet after receiving ICMPv6 Too Big message with MTU field less than IPV6_MIN_MTU
According to RFC2460, PMTU is set to the IPv6 Minimum Link MTU (1280) and a fragment header should always be included after a node receiving Too Big message reporting PMTU is less than the IPv6 Minimum Link MTU.
After receiving a ICMPv6 Too Big message reporting PMTU is less than the IPv6 Minimum Link MTU, sctp *can't* send any data/control chunk that total length including IPv6 head and IPv6 extend head is less than IPV6_MIN_MTU(1280 bytes).
The failure occured in p6_fragment(), about reason see following(take SHUTDOWN chunk for example):sctp_packet_transmit (SHUTDOWN chunk, len byte) |------sctp_v6_xmit (local_df=0)
|------ip6_xmit
|------ip6_output (dst_allfrag is ture)
|------ip6_fragmentIn ip6_fragment(), for local_df=0, drops the the packet and returns EMSGSIZE.
The patch fixes it with adding check length of skb->len. In this case, Ipv6 not to fragment upper protocol data, just only add a fragment header before it.
--- net/ipv6/ip6_output.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
net/ipv6/ip6_output.c +1 -1
@@ -625,7 +625,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))/* We must not fragment if the socket is set to force MTU discovery * or if the skb it not generated by a local socket. */ -if (!skb->local_df) { +if (!skb->local_df && skb->len > mtu) { skb->dev =skb_dst (skb)->dev;icmpv6_send (skb,ICMPV6_PKT_TOOBIG ,0 , mtu); IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
--
1.6.3.3
�
Herbert Xu wrote, at 04/19/2010 11:55 AM:
Quoted 2 lines
The patch looks good to me.
Thanks for reviewing this patch.
Quoted 6 lines
If we wanted to optimise the allfrags case it may be better to reserve the space beforehand and generate the fragment header at the same time as we're doing the IPv6 header.
But it can't be all that important as it's been broken for so many years.
If somebody needs one patch to fix the broken,
I am pleased to do so.
Signature · 3 lines
Best Regards ----- Shan Wei
Quoted 2 lines
Thanks,
David Miller
maintainerFrom: Herbert Xu <[email protected]>
Date: Mon, 19 Apr 2010 11:55:35 +0800
Quoted 29 lines · Shan Wei
Quoted 19 lines
According to RFC2460, PMTU is set to the IPv6 Minimum Link MTU (1280) and a fragment header should always be included after a node receiving Too Big message reporting PMTU is less than the IPv6 Minimum Link MTU.
After receiving a ICMPv6 Too Big message reporting PMTU is less than the IPv6 Minimum Link MTU, sctp *can't* send any data/control chunk that total length including IPv6 head and IPv6 extend head is less than
IPV6_MIN_MTU(1280 bytes).The failure occured in
p6_fragment(), about reason see following(take SHUTDOWN chunk for example):sctp_packet_transmit(SHUTDOWN chunk, len=16 byte) |------sctp_v6_xmit (local_df=0)
|------ip6_xmit|------ip6_output (dst_allfrag is ture) |------ip6_fragmentQuoted 8 lines
In
ip6_fragment(), for local_df=0, drops the the packet and returns EMSGSIZE.The patch fixes it with adding check length of
skb->len. In this case, Ipv6 not to fragment upper protocol data, just only add a fragment header before it.Signed-off-by Shan Wei <[email protected]>
Quoted 8 lines
The patch looks good to me.
If we wanted to optimise the allfrags case it may be better to reserve the space beforehand and generate the fragment header at the same time as we're doing the IPv6 header.
But it can't be all that important as it's been broken for so many years.
Right, I've applied Shan's patch, thanks.