* [PATCH -next crap] net: icmp: work around bogus pmtu errors
@ 2015-07-10 23:56 Florian Westphal
2015-07-14 22:40 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Florian Westphal @ 2015-07-10 23:56 UTC (permalink / raw)
To: netdev; +Cc: Florian Westphal
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.
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:
--
2.0.5
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH -next crap] net: icmp: work around bogus pmtu errors
2015-07-10 23:56 [PATCH -next crap] net: icmp: work around bogus pmtu errors Florian Westphal
@ 2015-07-14 22:40 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2015-07-14 22:40 UTC (permalink / raw)
To: fw; +Cc: netdev
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.
^ permalink raw reply [flat|nested] 2+ messages in thread
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