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Date:   Wed, 1 Jul 2020 12:22:41 +1000
From:   Herbert Xu <>
To:     Eric Dumazet <>
Cc:     Mathieu Desnoyers <>,
        David Miller <>,
        Linus Torvalds <>,
        LKML <>,
        netdev <>,
        Yuchung Cheng <>,
        Jonathan Rajotte-Julien <>
Subject: Re: [regression] TCP_MD5SIG on established sockets

On Tue, Jun 30, 2020 at 07:17:46PM -0700, Eric Dumazet wrote:
> The main issue of the prior code was the double read of key->keylen in
> tcp_md5_hash_key(), not that few bytes could change under us.
> I used smp_rmb() to ease backports, since old kernels had no
> READ_ONCE()/WRITE_ONCE(), but ACCESS_ONCE() instead.

If it's the double-read that you're protecting against, you should
just use barrier() and the comment should say so too.

Email: Herbert Xu <>
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