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References: <20201023111352.GA289522@rdias-suse-pc.lan>
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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 23 Oct 2020 16:03:27 +0200
Message-ID: <CANn89iJDt=XpUZA_uYK98cK8tctW6M=f4RFtGQpTxRaqwnnqSQ@mail.gmail.com>
Subject: Re: [PATCH] tcp: fix race condition when creating child sockets from syncookies
To:     Ricardo Dias <rdias@memsql.com>
Cc:     David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Oct 23, 2020 at 1:14 PM Ricardo Dias <rdias@memsql.com> wrote:
>
> When the TCP stack is in SYN flood mode, the server child socket is
> created from the SYN cookie received in a TCP packet with the ACK flag
> set.
>
...

This patch only handles IPv4, unless I am missing something ?

It looks like the fix should be done in inet_ehash_insert(), not
adding yet another helper in TCP.
This would be family generic.

Note that normally, all packets for the same 4-tuple should be handled
by the same cpu,
so this race is quite unlikely to happen in standard setups.