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

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Message-Id: <20200701.173112.1978013933888714889.davem@davemloft.net>
Date:   Wed, 01 Jul 2020 17:31:12 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        mathieu.desnoyers@...icios.com, herbert@...dor.apana.org.au,
        elver@...gle.com
Subject: Re: [PATCH v2 net] tcp: md5: refine
 tcp_md5_do_add()/tcp_md5_hash_key() barriers

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed,  1 Jul 2020 11:43:04 -0700

> 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>

Applied and queued up for -stable, thanks Eric.