netdev - Re: [PATCH net] ipv4/route: do not check saddr dev if iif is LOOPBACK

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Message-ID: <6fe3318a-727d-99c1-078d-2ba879de3749@gmail.com>
Date:   Mon, 12 Aug 2019 18:23:04 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stefano Brivio <sbrivio@...hat.com>,
        David Miller <davem@...emloft.net>
Cc:     liuhangbin@...il.com, netdev@...r.kernel.org, mleitner@...hat.com
Subject: Re: [PATCH net] ipv4/route: do not check saddr dev if iif is
 LOOPBACK_IFINDEX

On 8/12/19 4:58 PM, Stefano Brivio wrote:
> How so, actually? I don't see how that would happen. On the forwarding
> path, 'iif' is set (not to loopback interface), so that's not affected.
> 
> Is there any other route lookup possibility I'm missing?

Use case is saddr is set and FLOWI_FLAG_ANYSRC is not set and that seems
pretty common to me. From a quick look, icmp_route_lookup,
ipv4_update_pmtu, ipv4_redirect, inet_csk_route_req, ...

Enable trace_fib_table_lookup and look at the flags for various use cases.