linux-kernel - Re: [PATCH] netfilter: Force fake conntrack entry to be at least 8 bytes aligned

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Message-ID: <20170313123332.GA6790@salvia>
Date:   Mon, 13 Mar 2017 13:33:32 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Florian Westphal <fw@...len.de>
Cc:     "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        coreteam@...filter.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] netfilter: Force fake conntrack entry to be at least 8
 bytes aligned

On Sat, Mar 11, 2017 at 10:12:22AM +0100, Florian Westphal wrote:
> Steven Rostedt (VMware) <rostedt@...dmis.org> wrote:
> > Since the nfct and nfctinfo have been combined, the nf_conn structure
> > must be at least 8 bytes aligned, as the 3 LSB bits are used for the
> > nfctinfo. But there's a fake nf_conn structure to denote untracked
> > connections, which is created by a PER_CPU construct. This does not
> > guarantee that it will be 8 bytes aligned and can break the logic in
> > determining the correct nfctinfo.
> > 
> > I triggered this on a 32bit machine with the following error:
> [..]
> 
> Ugh.  Originally I had planned to also submit followup changes
> to get rid of the untracked objects but that part got delayed.
> 
> > By using DEFINE/DECLARE_PER_CPU_ALIGNED we can enforce at least 8 byte
> > alignment as all cache line sizes are at least 8 bytes or more.
> 
> Thanks for fixing this!
> 
> Acked-by: Florian Westphal <fw@...len.de>

Applied, thanks.