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Date:   Wed, 1 Jul 2020 12:22:41 +1000
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Eric Dumazet <edumazet@google.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        David Miller <davem@davemloft.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Yuchung Cheng <ycheng@google.com>,
        Jonathan Rajotte-Julien <joraj@efficios.com>
Subject: Re: [regression] TCP_MD5SIG on established sockets
Message-ID: <20200701022241.GA7167@gondor.apana.org.au>
References: <CANn89iLPqtJG0iESCHF+RcOjo95ukan1oSzjkPjoSJgKpO2wSQ@mail.gmail.com>
 <20200701020211.GA6875@gondor.apana.org.au>
 <CANn89iKP-evuLxeLo6p_98T+FuJ-J5YaMTRG230nqj3R=43tVA@mail.gmail.com>
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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.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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