netdev - Re: PMTUD broken inside network namespace with multipath routing

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Message-ID: <2f0e9d12-1780-cd1f-891d-940274f9105d@gmail.com>
Date:   Tue, 1 Sep 2020 18:42:10 -0600
From:   David Ahern <dsahern@...il.com>
To:     mastertheknife <mastertheknife@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: PMTUD broken inside network namespace with multipath routing

On 9/1/20 4:40 AM, mastertheknife wrote:
> 
> P.S: while reading the relevant code in the kernel, i think i spotted
> some mistake in net/ipv4/route.c, in function "update_or_create_fnhe".
> It looks like it loops over all the exceptions for the nexthop entry,
> but always overwriting the first (and only) entry, so effectively only
> 1 exception can exist per nexthop entry.
> Line 678:
> "if (fnhe) {"
> Should probably be:
> "if (fnhe && fnhe->fnhe_daddr == daddr) {"
> 

Right above that line is:

        for (fnhe = rcu_dereference(hash->chain); fnhe;
             fnhe = rcu_dereference(fnhe->fnhe_next)) {
                if (fnhe->fnhe_daddr == daddr)
                        break;
                depth++;
        }

so fnhe is set based on daddr match.