netdev - Re: [PATCH net] tcp: md5: allow changing MD5 keys in all socket states

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Date:   Thu, 02 Jul 2020 14:08:42 -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: allow changing MD5 keys in all socket
 states

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed,  1 Jul 2020 18:39:33 -0700

> This essentially reverts commit 721230326891 ("tcp: md5: reject TCP_MD5SIG
> or TCP_MD5SIG_EXT on established sockets")
> 
> Mathieu reported that many vendors BGP implementations can
> actually switch TCP MD5 on established flows.
> 
> Quoting Mathieu :
>    Here is a list of a few network vendors along with their behavior
>    with respect to TCP MD5:
> 
>    - Cisco: Allows for password to be changed, but within the hold-down
>      timer (~180 seconds).
>    - Juniper: When password is initially set on active connection it will
>      reset, but after that any subsequent password changes no network
>      resets.
>    - Nokia: No notes on if they flap the tcp connection or not.
>    - Ericsson/RedBack: Allows for 2 password (old/new) to co-exist until
>      both sides are ok with new passwords.
>    - Meta-Switch: Expects the password to be set before a connection is
>      attempted, but no further info on whether they reset the TCP
>      connection on a change.
>    - Avaya: Disable the neighbor, then set password, then re-enable.
>    - Zebos: Would normally allow the change when socket connected.
> 
> We can revert my prior change because commit 9424e2e7ad93 ("tcp: md5: fix potential
> overestimation of TCP option space") removed the leak of 4 kernel bytes to
> the wire that was the main reason for my patch.
> 
> While doing my investigations, I found a bug when a MD5 key is changed, leading
> to these commits that stable teams want to consider before backporting this revert :
> 
>  Commit 6a2febec338d ("tcp: md5: add missing memory barriers in tcp_md5_do_add()/tcp_md5_hash_key()")
>  Commit e6ced831ef11 ("tcp: md5: refine tcp_md5_do_add()/tcp_md5_hash_key() barriers")
> 
> Fixes: 721230326891 "tcp: md5: reject TCP_MD5SIG or TCP_MD5SIG_EXT on established sockets"
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Applied and queued up for -stable with those other two commits.

Thanks!