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From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Wed, 29 Jan 2025 13:24:32 +0100
Subject: [PATCH net 1/2] mptcp: blackhole only if 1st SYN retrans w/o MPC
is accepted
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Message-Id: <20250129-net-mptcp-blackhole-fix-v1-1-afe88e5a6d2c@kernel.org>
References: <20250129-net-mptcp-blackhole-fix-v1-0-afe88e5a6d2c@kernel.org>
In-Reply-To: <20250129-net-mptcp-blackhole-fix-v1-0-afe88e5a6d2c@kernel.org>
To: mptcp@lists.linux.dev, Mat Martineau <martineau@kernel.org>,
Geliang Tang <geliang@kernel.org>, "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
Jonathan Corbet <corbet@lwn.net>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, "Matthieu Baerts (NGI0)" <matttbe@kernel.org>,
stable@vger.kernel.org
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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 <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
net/mptcp/ctrl.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 3999e0ba2c35b50c36ce32277e0b8bfb24197946..2dd81e6c26bdb5220abed68e26d=
70d2dc3ab14fb 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -418,9 +418,9 @@ void mptcp_active_detect_blackhole(struct sock *ssk, bo=
ol expired)
MPTCP_INC_STATS(net, MPTCP_MIB_MPCAPABLEACTIVEDROP);
subflow->mpc_drop =3D 1;
mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow);
- } else {
- subflow->mpc_drop =3D 0;
}
+ } else if (ssk->sk_state =3D=3D TCP_SYN_SENT) {
+ subflow->mpc_drop =3D 0;
}
}
=20
--=20
2.47.1
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From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Wed, 29 Jan 2025 13:24:33 +0100
Subject: [PATCH net 2/2] doc: mptcp: sysctl: blackhole_timeout is per-netns
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To: mptcp@lists.linux.dev, Mat Martineau <martineau@kernel.org>,
Geliang Tang <geliang@kernel.org>, "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
Jonathan Corbet <corbet@lwn.net>
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All other sysctl entries mention it, and it is a per-namespace sysctl.
So mention it as well.
Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole")
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Documentation/networking/mptcp-sysctl.rst | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/networking/mptcp-sysctl.rst b/Documentation/netw=
orking/mptcp-sysctl.rst
index dc45c02113537b98dff76a6ed431c0449b5217f8..03e1d3610333e29423b0f40591c=
9e914dc2d0366 100644
--- a/Documentation/networking/mptcp-sysctl.rst
+++ b/Documentation/networking/mptcp-sysctl.rst
@@ -41,7 +41,7 @@ blackhole_timeout - INTEGER (seconds)
MPTCP is re-enabled and will reset to the initial value when the
blackhole issue goes away.
=20
- 0 to disable the blackhole detection.
+ 0 to disable the blackhole detection. This is a per-namespace sysctl.
=20
Default: 3600
=20
--=20
2.47.1