netdev - [PATCH net] mptcp: fix race in msk status update

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Message-Id: <4d5e3c09ca38a0a3ec951fa4f5bfc65d5cd40129.1587725562.git.pabeni@redhat.com>
Date:   Fri, 24 Apr 2020 13:15:21 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Davide Caratti <dcaratti@...hat.com>, mptcp@...ts.01.org
Subject: [PATCH net] mptcp: fix race in msk status update

Currently subflow_finish_connect() changes unconditionally
any msk socket status other than TCP_ESTABLISHED.

If an unblocking connect() races with close(), we can end-up
triggering:

IPv4: Attempt to release TCP socket in state 1 00000000e32b8b7e

when the msk socket is disposed.

Be sure to enter the established status only from SYN_SENT.

Fixes: c3c123d16c0e ("net: mptcp: don't hang in mptcp_sendmsg() after TCP fallback")
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
Note: the issue is possibly older, but this fix applies only
on the mentioned commit
---
 net/mptcp/subflow.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 87c094702d63..2488e011048c 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -225,7 +225,7 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 
 	subflow->icsk_af_ops->sk_rx_dst_set(sk, skb);
 
-	if (inet_sk_state_load(parent) != TCP_ESTABLISHED) {
+	if (inet_sk_state_load(parent) == TCP_SYN_SENT) {
 		inet_sk_state_store(parent, TCP_ESTABLISHED);
 		parent->sk_state_change(parent);
 	}
-- 
2.21.1