From: Matthieu Baerts (NGI0) Date: Wed, 29 Jan 2025 12:24:32 +0000 (+0100) Subject: mptcp: blackhole only if 1st SYN retrans w/o MPC is accepted X-Git-Tag: v6.13.2~22 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=be2c5f7ff6b60946c8abf26893859a9be4f4377a;p=thirdparty%2Fkernel%2Fstable.git mptcp: blackhole only if 1st SYN retrans w/o MPC is accepted commit e598d8981fd34470b78a1ae777dbf131b15d5bf2 upstream. The Fixes commit mentioned this: > An MPTCP firewall blackhole can be detected if the following SYN > retransmission after a fallback to "plain" TCP is accepted. But in fact, this blackhole was detected if any following SYN retransmissions after a fallback to TCP was accepted. That's because 'mptcp_subflow_early_fallback()' will set 'request_mptcp' to 0, and 'mpc_drop' will never be reset to 0 after. This is an issue, because some not so unusual situations might cause the kernel to detect a false-positive blackhole, e.g. a client trying to connect to a server while the network is not ready yet, causing a few SYN retransmissions, before reaching the end server. Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole") Cc: stable@vger.kernel.org Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c index b0dd008e2114b..dd595d9b5e50c 100644 --- a/net/mptcp/ctrl.c +++ b/net/mptcp/ctrl.c @@ -405,9 +405,9 @@ void mptcp_active_detect_blackhole(struct sock *ssk, bool expired) MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPCAPABLEACTIVEDROP); subflow->mpc_drop = 1; mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow); - } else { - subflow->mpc_drop = 0; } + } else if (ssk->sk_state == TCP_SYN_SENT) { + subflow->mpc_drop = 0; } }