linux-kernel - [PATCH net 1/2] mptcp: don't orphan ssk in mptcp

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Message-Id: <20221128154239.1999234-2-matthieu.baerts@tessares.net>
Date:   Mon, 28 Nov 2022 16:42:37 +0100
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Davide Caratti <dcaratti@...hat.com>
Cc:     Menglong Dong <imagedong@...cent.com>,
        Biao Jiang <benbjiang@...cent.com>,
        Mengen Sun <mengensun@...cent.com>, netdev@...r.kernel.org,
        mptcp@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: [PATCH net 1/2] mptcp: don't orphan ssk in mptcp_close()

From: Menglong Dong <imagedong@...cent.com>

All of the subflows of a msk will be orphaned in mptcp_close(), which
means the subflows are in DEAD state. After then, DATA_FIN will be sent,
and the other side will response with a DATA_ACK for this DATA_FIN.

However, if the other side still has pending data, the data that received
on these subflows will not be passed to the msk, as they are DEAD and
subflow_data_ready() will not be called in tcp_data_ready(). Therefore,
these data can't be acked, and they will be retransmitted again and again,
until timeout.

Fix this by setting ssk->sk_socket and ssk->sk_wq to 'NULL', instead of
orphaning the subflows in __mptcp_close(), as Paolo suggested.

Fixes: e16163b6e2b7 ("mptcp: refactor shutdown and close")
Reviewed-by: Biao Jiang <benbjiang@...cent.com>
Reviewed-by: Mengen Sun <mengensun@...cent.com>
Signed-off-by: Menglong Dong <imagedong@...cent.com>
Reviewed-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@...sares.net>
---
 net/mptcp/protocol.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index b6dc6e260334..1dbc62537259 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2354,12 +2354,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 		goto out;
 	}
 
-	/* if we are invoked by the msk cleanup code, the subflow is
-	 * already orphaned
-	 */
-	if (ssk->sk_socket)
-		sock_orphan(ssk);
-
+	sock_orphan(ssk);
 	subflow->disposable = 1;
 
 	/* if ssk hit tcp_done(), tcp_cleanup_ulp() cleared the related ops
@@ -2940,7 +2935,11 @@ bool __mptcp_close(struct sock *sk, long timeout)
 		if (ssk == msk->first)
 			subflow->fail_tout = 0;
 
-		sock_orphan(ssk);
+		/* detach from the parent socket, but allow data_ready to
+		 * push incoming data into the mptcp stack, to properly ack it
+		 */
+		ssk->sk_socket = NULL;
+		ssk->sk_wq = NULL;
 		unlock_sock_fast(ssk, slow);
 	}
 	sock_orphan(sk);
-- 
2.37.2