netdev - [PATCH net 2/9] mptcp: do not rely on implicit state check in mptcp

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Date: Tue, 04 Jul 2023 22:44:34 +0200
From: Matthieu Baerts <matthieu.baerts@...sares.net>
To: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Shuah Khan <shuah@...nel.org>, Florian Westphal <fw@...len.de>, 
 Kishen Maloor <kishen.maloor@...el.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, 
 Matthieu Baerts <matthieu.baerts@...sares.net>, stable@...r.kernel.org, 
 Christoph Paasch <cpaasch@...le.com>
Subject: [PATCH net 2/9] mptcp: do not rely on implicit state check in
 mptcp_listen()

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

Since the blamed commit, closing the first subflow resets the first
subflow socket state to SS_UNCONNECTED.

The current mptcp listen implementation relies only on such
state to prevent touching not-fully-disconnected sockets.

Incoming mptcp fastclose (or paired endpoint removal) unconditionally
closes the first subflow.

All the above allows an incoming fastclose followed by a listen() call
to successfully race with a blocking recvmsg(), potentially causing the
latter to hit a divide by zero bug in cleanup_rbuf/__tcp_select_window().

Address the issue explicitly checking the msk socket state in
mptcp_listen(). An alternative solution would be moving the first
subflow socket state update into mptcp_disconnect(), but in the long
term the first subflow socket should be removed: better avoid relaying
on it for internal consistency check.

Fixes: b29fcfb54cd7 ("mptcp: full disconnect implementation")
Cc: stable@...r.kernel.org
Reported-by: Christoph Paasch <cpaasch@...le.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/414
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@...sares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@...sares.net>
---
 net/mptcp/protocol.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 489a3defdde5..3613489eb6e3 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3703,6 +3703,11 @@ static int mptcp_listen(struct socket *sock, int backlog)
 	pr_debug("msk=%p", msk);

 	lock_sock(sk);
+
+	err = -EINVAL;
+	if (sock->state != SS_UNCONNECTED || sock->type != SOCK_STREAM)
+		goto unlock;
+
 	ssock = __mptcp_nmpc_socket(msk);
 	if (IS_ERR(ssock)) {
 		err = PTR_ERR(ssock);

-- 
2.40.1