netdev - Re: [PATCH net v2] udp: preserve skb->dst if required for IP options processing

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Message-ID: <20170721105346.tsspktxszzt4tgvs@shodan.usersys.redhat.com>
Date:   Fri, 21 Jul 2017 12:53:46 +0200
From:   Artem Savkov <asavkov@...hat.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net v2] udp: preserve skb->dst if required for IP options
 processing

On Tue, Jul 18, 2017 at 11:57:55AM +0200, Paolo Abeni wrote:
> Eric noticed that in udp_recvmsg() we still need to access
> skb->dst while processing the IP options.
> Since commit 0a463c78d25b ("udp: avoid a cache miss on dequeue")
> skb->dst is no more available at recvmsg() time and bad things
> will happen if we enter the relevant code path.
> 
> This commit address the issue, avoid clearing skb->dst if
> any IP options are present into the relevant skb.
> Since the IP CB is contained in the first skb cacheline, we can
> test it to decide to leverage the consume_stateless_skb()
> optimization, without measurable additional cost in the faster
> path.

This doesn't seem to be enough for XFRM case. CMSG gets eaten up in
selinux-testsuite[1]/inet_socket test in ipsec configuration.

[1] https://github.com/SELinuxProject/selinux-testsuite.git

-- 
Regards,
  Artem