>
https://bugzilla.kernel.org/show_bug.cgi?id=15682
>
> Summary: XFRM is not updating RTAX_ADVMSS metric
> Product: Networking
> Version: 2.5
> Kernel Version: 2.6.28-2
> Platform: All
> OS/Version: Linux
> Tree: Mainline
> Status: NEW
> Severity: normal
> Priority: P1
> Component: Other
> AssignedTo:
acme@ghostprotocols.net
> ReportedBy:
eduardo.panisset@gmail.com
> Regression: No
>
>
> I have been testing DSMIPv6 code which uses all kind of advanced
> features of XFRM framework and I believe I have found a bug related to
> update RTAX_ADVMSS route metric.
> The XFRM code on net/xfrm/xfrm_policy.c by its functions
> xfrm_init_pmtu and xfrm_bundle_ok updates RTAX_MTU route caching
> metric however I believe it must update RTAX_ADVMSS as this later is
> used by tcp connect function for adverting the MSS value on SYN
> messages.
>
> As MSS is not being updated by XFRM the TCP SYN messages (e.g.
> originated from a internet browser) is erroneously informing its MSS
> (without taking into account the overhead added to IP packet size by
> XFRM transformations). One result of that is the browser gets
> "frozen" after starts a TCP connection because TCP messages sent by
> TCP server will never get to it (TCP server is sending too large
> segments to browser).
>
> Below I describe the changes I have done (on xfrm_init_pmtu and
> xfrm_bundle_ok) and that seem to fix this problem:
>
> xfrm_init_pmtu:
> .
> .
> .
>
> dst->metrics[RTAX_MTU-1] = pmtu; // original code, below my changes
>
> if (dst->xfrm->props.mode == XFRM_MODE_TUNNEL)
> switch (dst->xfrm->props.family)
> {
> case AF_INET:
> dst->metrics[RTAX_ADVMSS-1] = max_t(unsigned int,
> pmtu - sizeof(struct iphdr) - sizeof(struct tcphdr), 256);
> break;
>
> case AF_INET6:
> dst->metrics[RTAX_ADVMSS-1] = max_t(unsigned int,
> pmtu - sizeof(struct ipv6hdr) - sizeof(struct tcphdr),
> dev_net(dst->dev)->ipv6.
> sysctl.ip6_rt_min_advmss);
> break;
> }
>
> xfrm_bundle_ok:
>
> .
> .
> .
>
> dst->metrics[RTAX_MTU-1] = mtu; // original code, below my changes
>
> if (dst->xfrm->props.mode == XFRM_MODE_TUNNEL)
> switch (dst->xfrm->props.family)
> {
> case AF_INET:
> dst->metrics[RTAX_ADVMSS-1] = max_t(unsigned
> int, mtu - sizeof(struct iphdr) - sizeof(struct tcphdr), 256);
> break;
>
> case AF_INET6:
> dst->metrics[RTAX_ADVMSS-1] = max_t(unsigned
> int, mtu - sizeof(struct ipv6hdr) - sizeof(struct tcphdr),
>
> dev_net(dst->dev)->ipv6.sysctl.ip6_rt_min_advmss);
> break;
> }
>
