netdev - Re: [PATCH net] net: ipv4: Make "ip route get" match iif lo rules again.

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Message-Id: <20180115.135419.992724517936932654.davem@davemloft.net>
Date:   Mon, 15 Jan 2018 13:54:19 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     lorenzo@...gle.com
Cc:     netdev@...r.kernel.org, dsahern@...il.com, rami.rosen@...el.com,
        nikolay@...ulusnetworks.com, roopa@...ulusnetworks.com
Subject: Re: [PATCH net] net: ipv4: Make "ip route get" match iif lo rules
 again.

From: Lorenzo Colitti <lorenzo@...gle.com>
Date: Thu, 11 Jan 2018 18:36:26 +0900

> Commit 3765d35ed8b9 ("net: ipv4: Convert inet_rtm_getroute to rcu
> versions of route lookup") broke "ip route get" in the presence
> of rules that specify iif lo.
> 
> Host-originated traffic always has iif lo, because
> ip_route_output_key_hash and ip6_route_output_flags set the flow
> iif to LOOPBACK_IFINDEX. Thus, putting "iif lo" in an ip rule is a
> convenient way to select only originated traffic and not forwarded
> traffic.
> 
> inet_rtm_getroute used to match these rules correctly because
> even though it sets the flow iif to 0, it called
> ip_route_output_key which overwrites iif with LOOPBACK_IFINDEX.
> But now that it calls ip_route_output_key_hash_rcu, the ifindex
> will remain 0 and not match the iif lo in the rule. As a result,
> "ip route get" will return ENETUNREACH.
> 
> Fixes: 3765d35ed8b9 ("net: ipv4: Convert inet_rtm_getroute to rcu versions of route lookup")
> Tested: https://android.googlesource.com/kernel/tests/+/master/net/test/multinetwork_test.py passes again
> Signed-off-by: Lorenzo Colitti <lorenzo@...gle.com>

Applied and queued up for -stable, thanks!