From: Eric Dumazet <[email protected]>
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 <[email protected]>
> Reported-by: Mathieu Desnoyers <[email protected]>
Applied and queued up for -stable with those other two commits.
Thanks!
