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 17:55:13 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH net] tcp: md5: add missing memory barriers in tcp_md5_do_add()/tcp_md5_hash_key()

On Tue, Jun 30, 2020 at 5:53 PM Hideaki Yoshifuji
<hideaki.yoshifuji@...aclelinux.com> wrote:
>
> Hi,
>
> 2020年7月1日(水) 8:41 Eric Dumazet <edumazet@...gle.com>:
> :
> > 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>
> > ---
> >  net/ipv4/tcp.c      | 7 +++++--
> >  net/ipv4/tcp_ipv4.c | 3 +++
> >  2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 810cc164f795f8e1e8ca747ed5df51bb20fec8a2..f111660453241692a17c881dd6dc2910a1236263 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -4033,10 +4033,13 @@ EXPORT_SYMBOL(tcp_md5_hash_skb_data);
> >
> >  int tcp_md5_hash_key(struct tcp_md5sig_pool *hp, const struct tcp_md5sig_key *key)
> >  {
> > +       u8 keylen = key->keylen;
> >         struct scatterlist sg;
>
> ACCESS_ONCE here, no?

Not needed, the smp_rmb() barrier is stronger.