From: Eric Dumazet edumazet@google.com
[ Upstream commit 1ca0fafd73c5268e8fc4b997094b8bb2bfe8deea ]
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@google.com Reported-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
--- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -2759,10 +2759,7 @@ static int do_tcp_setsockopt(struct sock #ifdef CONFIG_TCP_MD5SIG case TCP_MD5SIG: case TCP_MD5SIG_EXT: - if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) - err = tp->af_specific->md5_parse(sk, optname, optval, optlen); - else - err = -EINVAL; + err = tp->af_specific->md5_parse(sk, optname, optval, optlen); break; #endif case TCP_USER_TIMEOUT: