netdev - Re: [PATCH net] tcp: md5: add missing memory barriers in tcp_md5_do_add()/tcp_md5_hash

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Date:   Tue, 30 Jun 2020 18:15:46 -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
Subject: Re: [PATCH net] tcp: md5: add missing memory barriers in
 tcp_md5_do_add()/tcp_md5_hash_key()

From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 30 Jun 2020 16:41:01 -0700

> MD5 keys are read with RCU protection, and tcp_md5_do_add()
> might update in-place a prior key.
> 
> Normally, typical RCU updates would allocate a new piece
> of memory. In this case only key->key and key->keylen might
> be updated, and we do not care if an incoming packet could
> see the old key, the new one, or some intermediate value,
> since changing the key on a live flow is known to be problematic
> anyway.
> 
> We only want to make sure that in the case key->keylen
> is changed, cpus in tcp_md5_hash_key() wont try to use
> uninitialized data, or crash because key->keylen was
> read twice to feed sg_init_one() and ahash_request_set_crypt()
> 
> Fixes: 9ea88a153001 ("tcp: md5: check md5 signature without socket lock")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Applied and queued up for -stable, thanks Eric.