linux-kernel - Re: [regression] TCP_MD5SIG on established sockets

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Date:   Wed, 1 Jul 2020 12:22:41 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        David Miller <davem@...emloft.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Jonathan Rajotte-Julien <joraj@...icios.com>
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.

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