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

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Date:   Thu, 16 May 2019 21:24:36 +0000
From:   Martin Lau <kafai@...com>
To:     Wei Wang <tracywwnj@...il.com>
CC:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Wei Wang <weiwan@...gle.com>,
        Mikael Magnusson <mikael.kernel@...ts.m7n.se>,
        David Ahern <dsahern@...il.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v3 net] ipv6: fix src addr routing with the exception
 table

On Thu, May 16, 2019 at 01:30:54PM -0700, Wei Wang wrote:
> 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>
> Cc: Martin Lau <kafai@...com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> ---
> Changes from v2:
> - modified the check in rt6_find_cached_rt() to prevent infinite loop
> - add const to src_key to prevent kernel compile warning
> 
> Changes from v1:
> - restructure the code to only include the new logic in
>   rt6_find_cached_rt()
Acked-by: Martin KaFai Lau <kafai@...com>

Thanks for the fix and changes!