netdev - Re: [PATCH net-next] ipv6: Convert gateway validation to use fib6

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Date:   Fri, 21 Jun 2019 15:04:42 -0600
From:   David Ahern <dsahern@...il.com>
To:     Wei Wang <weiwan@...gle.com>, David Ahern <dsahern@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH net-next] ipv6: Convert gateway validation to use
 fib6_info

On 6/20/19 5:43 PM, Wei Wang wrote:
> I am not very convinced that fib6_lookup() could be equivalent to
> rt6_lookup(). Specifically, rt6_lookup() calls rt6_device_match()
> while fib6_lookup() calls rt6_select() to match the oif. From a brief
> glance, it does seem to be similar, especially considering that saddr
> is NULL. So it probably is OK?

When you remove the rt6_check_neigh call since RT6_LOOKUP_F_REACHABLE is
not set that removes the RT6_NUD_FAIL_DO_RR return and round-robin
logic. I am reasonably confident that given the use case - validate the
gateway and optionally given the device - it is the same.

rt6_select is much more complicated than rt6_device_match, so there is a
small possibility that in some corner case gateway validation fails /
succeeds with fib6_table_lookup where it would succeed / fail with
ip6_pol_route_lookup. But, ip6_pol_route and fib6_table_lookup is the
code path actually used for packet Rx and Tx, so it seems to me to be
the more proper one for gateway validation.

I will send a v2 with idev change you mentioned.