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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Xin Tan <tanxin.ctf@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.19 25/56] net/x25: Fix x25_neigh refcnt leak when x25 disconnect
Date:   Mon,  3 Aug 2020 14:19:40 +0200
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From: Xiyu Yang <xiyuyang19@fudan.edu.cn>

commit 4becb7ee5b3d2829ed7b9261a245a77d5b7de902 upstream.

x25_connect() invokes x25_get_neigh(), which returns a reference of the
specified x25_neigh object to "x25->neighbour" with increased refcnt.

When x25 connect success and returns, the reference still be hold by
"x25->neighbour", so the refcount should be decreased in
x25_disconnect() to keep refcount balanced.

The reference counting issue happens in x25_disconnect(), which forgets
to decrease the refcnt increased by x25_get_neigh() in x25_connect(),
causing a refcnt leak.

Fix this issue by calling x25_neigh_put() before x25_disconnect()
returns.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/x25/x25_subr.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/x25/x25_subr.c
+++ b/net/x25/x25_subr.c
@@ -362,6 +362,10 @@ void x25_disconnect(struct sock *sk, int
 		sk->sk_state_change(sk);
 		sock_set_flag(sk, SOCK_DEAD);
 	}
+	read_lock_bh(&x25_list_lock);
+	x25_neigh_put(x25->neighbour);
+	x25->neighbour = NULL;
+	read_unlock_bh(&x25_list_lock);
 }
 
 /*