| Message ID | 1436572609-2097-1-git-send-email-fw@strlen.de |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Florian Westphal <fw@strlen.de> Date: Sat, 11 Jul 2015 01:56:49 +0200 > sometimes tcp connections seem to hang. > tcpdump shows broken path mtu reports. This "fix" avoids hang and gives: > > [633.327834] icmp: 192.0.0.2 reports mtu 1474 for packet size 1474 to host 204.236.132.12 > [635.586945] icmp: 192.0.0.2 reports mtu 1474 for packet size 1474 to host 54.219.255.254 > [647.106708] icmp: 192.0.0.2 reports mtu 1474 for packet size 1466 to host 204.236.132.12 > [663.084586] icmp: 192.0.0.2 reports mtu 1474 for packet size 1466 to host 54.219.255.254 > > sigh. > > Signed-off-by: Florian Westphal <fw@strlen.de> > --- > Might be caused by DS-LITE. I either need the turd below or iptables TCPMSS > mangling rules to artificially lower received mss. > > I don't mind if this is rejected; I'm mostly wondering if anyone > else came across suprise like this. I think the culprit should be identified and fixed ASAP, the last thing we want is for every system add a hack like this. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index 36f5584..1ab08dd 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -771,6 +771,8 @@ static bool icmp_unreach(struct sk_buff *skb) goto out_err; if (icmph->type == ICMP_DEST_UNREACH) { + u16 tot_len; + switch (icmph->code & 15) { case ICMP_NET_UNREACH: case ICMP_HOST_UNREACH: @@ -795,6 +797,17 @@ static bool icmp_unreach(struct sk_buff *skb) /* fall through */ case 0: info = ntohs(icmph->un.frag.mtu); + + tot_len = ntohs(iph->tot_len); + + if (tot_len <= info) { + pr_warn_ratelimited("%pI4 reports mtu %d for packet" + " size %d to host %pI4\n", + &ip_hdr(skb)->saddr, info, + tot_len, &iph->daddr); + if (tot_len >= (536 + 8)) + info = tot_len - 8; + } } break; case ICMP_SR_FAILED:
sometimes tcp connections seem to hang. tcpdump shows broken path mtu reports. This "fix" avoids hang and gives: [633.327834] icmp: 192.0.0.2 reports mtu 1474 for packet size 1474 to host 204.236.132.12 [635.586945] icmp: 192.0.0.2 reports mtu 1474 for packet size 1474 to host 54.219.255.254 [647.106708] icmp: 192.0.0.2 reports mtu 1474 for packet size 1466 to host 204.236.132.12 [663.084586] icmp: 192.0.0.2 reports mtu 1474 for packet size 1466 to host 54.219.255.254 sigh. Signed-off-by: Florian Westphal <fw@strlen.de> --- Might be caused by DS-LITE. I either need the turd below or iptables TCPMSS mangling rules to artificially lower received mss. I don't mind if this is rejected; I'm mostly wondering if anyone else came across suprise like this.