netdev - Re: [PATCH v3 net] ipv6: fix src addr routing with the exception table

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Message-Id: <20190516.143346.1283734330002616092.davem@davemloft.net>
Date:   Thu, 16 May 2019 14:33:46 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     tracywwnj@...il.com
Cc:     netdev@...r.kernel.org, kafai@...com, weiwan@...gle.com,
        mikael.kernel@...ts.m7n.se, dsahern@...il.com, edumazet@...gle.com
Subject: Re: [PATCH v3 net] ipv6: fix src addr routing with the exception
 table

From: Wei Wang <tracywwnj@...il.com>
Date: Thu, 16 May 2019 13:30:54 -0700

> From: Wei Wang <weiwan@...gle.com>
> 
> When inserting route cache into the exception table, the key is
> generated with both src_addr and dest_addr with src addr routing.
> However, current logic always assumes the src_addr used to generate the
> key is a /128 host address. This is not true in the following scenarios:
> 1. When the route is a gateway route or does not have next hop.
>    (rt6_is_gw_or_nonexthop() == false)
> 2. When calling ip6_rt_cache_alloc(), saddr is passed in as NULL.
> This means, when looking for a route cache in the exception table, we
> have to do the lookup twice: first time with the passed in /128 host
> address, second time with the src_addr stored in fib6_info.
> 
> This solves the pmtu discovery issue reported by Mikael Magnusson where
> a route cache with a lower mtu info is created for a gateway route with
> src addr. However, the lookup code is not able to find this route cache.
> 
> Fixes: 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")
> Reported-by: Mikael Magnusson <mikael.kernel@...ts.m7n.se>
> Bisected-by: David Ahern <dsahern@...il.com>
> Signed-off-by: Wei Wang <weiwan@...gle.com>

Applied and queued up for -stable.