linux-kernel - [PATCH net-next] mptcp: reset blackhole on success with non-loopback ifaces

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Message-Id: <20250918-net-next-mptcp-blackhole-reset-loopback-v1-1-bf5818326639@kernel.org>
Date: Thu, 18 Sep 2025 10:50:18 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, 
 Kuniyuki Iwashima <kuniyu@...gle.com>
Subject: [PATCH net-next] mptcp: reset blackhole on success with
 non-loopback ifaces

When a first MPTCP connection gets successfully established after a
blackhole period, 'active_disable_times' was supposed to be reset when
this connection was done via any non-loopback interfaces.

Unfortunately, the opposite condition was checked: only reset when the
connection was established via a loopback interface. Fixing this by
simply looking at the opposite.

This is similar to what is done with TCP FastOpen, see
tcp_fastopen_active_disable_ofo_check().

This patch is a follow-up of a previous discussion linked to commit
893c49a78d9f ("mptcp: Use __sk_dst_get() and dst_dev_rcu() in
mptcp_active_enable()."), see [1].

Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole")
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/4209a283-8822-47bd-95b7-87e96d9b7ea3@kernel.org [1]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
Cc: Kuniyuki Iwashima <kuniyu@...gle.com>
Note: sending this fix to net-next, similar to commits 108a86c71c93
("mptcp: Call dst_release() in mptcp_active_enable().") and 893c49a78d9f
("mptcp: Use __sk_dst_get() and dst_dev_rcu() in mptcp_active_enable().").
Also to avoid conflicts, and because we are close to the merge windows.
---
 net/mptcp/ctrl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index e8ffa62ec183f3cd8156e3969ac4a7d0213a990b..d96130e49942e2fb878cd1897ad43c1d420fb233 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -507,7 +507,7 @@ void mptcp_active_enable(struct sock *sk)
 		rcu_read_lock();
 		dst = __sk_dst_get(sk);
 		dev = dst ? dst_dev_rcu(dst) : NULL;
-		if (dev && (dev->flags & IFF_LOOPBACK))
+		if (!(dev && (dev->flags & IFF_LOOPBACK)))
 			atomic_set(&pernet->active_disable_times, 0);
 		rcu_read_unlock();
 	}

---
base-commit: b127e355f1af1e4a635ed8f78cb0d11c916613cf
change-id: 20250918-net-next-mptcp-blackhole-reset-loopback-d82c518e409f

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@...nel.org>