netdev - [PATCH net 3/3] mptcp: safety check before fallback

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Message-Id: <20250224-net-mptcp-misc-fixes-v1-3-f550f636b435@kernel.org>
Date: Mon, 24 Feb 2025 19:11:52 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: mptcp@...ts.linux.dev, 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, linux-kernel@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH net 3/3] mptcp: safety check before fallback

Recently, some fallback have been initiated, while the connection was
not supposed to fallback.

Add a safety check with a warning to detect when an wrong attempt to
fallback is being done. This should help detecting any future issues
quicker.

Acked-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/protocol.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f6a207958459db5bd39f91ed7431b5a766669f92..ad21925af061263d908bd9faddffaef979f46c93 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1199,6 +1199,8 @@ static inline void __mptcp_do_fallback(struct mptcp_sock *msk)
 		pr_debug("TCP fallback already done (msk=%p)\n", msk);
 		return;
 	}
+	if (WARN_ON_ONCE(!READ_ONCE(msk->allow_infinite_fallback)))
+		return;
 	set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
 }

-- 
2.47.1