netdev - Re: [PATCH v2 net] tcp: md5: refine tcp_md5_do_add()/tcp_md5_hash

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Message-ID: <1217308675.19634.1593629282429.JavaMail.zimbra@efficios.com>
Date:   Wed, 1 Jul 2020 14:48:02 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH v2 net] tcp: md5: refine
 tcp_md5_do_add()/tcp_md5_hash_key() barriers

----- On Jul 1, 2020, at 2:43 PM, Eric Dumazet edumazet@...gle.com wrote:

> My prior fix went a bit too far, according to Herbert and Mathieu.
> 
> Since we accept that concurrent TCP MD5 lookups might see inconsistent
> keys, we can use READ_ONCE()/WRITE_ONCE() instead of smp_rmb()/smp_wmb()
> 
> Clearing all key->key[] is needed to avoid possible KMSAN reports,
> if key->keylen is increased. Since tcp_md5_do_add() is not fast path,
> using __GFP_ZERO to clear all struct tcp_md5sig_key is simpler.
> 
> data_race() was added in linux-5.8 and will prevent KCSAN reports,
> this can safely be removed in stable backports, if data_race() is
> not yet backported.
> 
> v2: use data_race() both in tcp_md5_hash_key() and tcp_md5_do_add()
> 
> Fixes: 6a2febec338d ("tcp: md5: add missing memory barriers in
> tcp_md5_do_add()/tcp_md5_hash_key()")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks !

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com