linux-kernel - [PATCH 5.10 192/289] mptcp: fix splat when closing unaccepted socket

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Date:   Mon, 17 May 2021 16:01:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Florian Westphal <fw@...len.de>,
        Paolo Abeni <pabeni@...hat.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 192/289] mptcp: fix splat when closing unaccepted socket

From: Paolo Abeni <pabeni@...hat.com>

[ Upstream commit 578c18eff1627d6a911f08f4cf351eca41fdcc7d ]

If userspace exits before calling accept() on a listener that had at least
one new connection ready, we get:

   Attempt to release TCP socket in state 8

This happens because the mptcp socket gets cloned when the TCP connection
is ready, but the socket is never exposed to userspace.

The client additionally sends a DATA_FIN, which brings connection into
CLOSE_WAIT state.  This in turn prevents the orphan+state reset fixup
in mptcp_sock_destruct() from doing its job.

Fixes: 3721b9b64676b ("mptcp: Track received DATA_FIN sequence number and add related helpers")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/185
Tested-by: Florian Westphal <fw@...len.de>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
Link: https://lore.kernel.org/r/20210507001638.225468-1-mathew.j.martineau@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/mptcp/subflow.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 6317b9bc8681..01a675fa2aa2 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -445,8 +445,7 @@ static void mptcp_sock_destruct(struct sock *sk)
 	 * ESTABLISHED state and will not have the SOCK_DEAD flag.
 	 * Both result in warnings from inet_sock_destruct.
 	 */
-
-	if (sk->sk_state == TCP_ESTABLISHED) {
+	if ((1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
 		sk->sk_state = TCP_CLOSE;
 		WARN_ON_ONCE(sk->sk_socket);
 		sock_orphan(sk);
-- 
2.30.2