linux-kernel - [PATCH v2] net/x25: Fix x25_neigh refcnt leak when x25 disconnect

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Date:   Sat, 25 Apr 2020 21:06:25 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     Andrew Hendry <andrew.hendry@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Allison Randal <allison@...utok.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu
Subject: [PATCH v2] net/x25: Fix x25_neigh refcnt leak when x25 disconnect

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@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
Changes in v2:
- Fix x25_neigh refcnt leak in x25_disconnect() rather than in
x25_connect()
---
 net/x25/x25_subr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/x25/x25_subr.c b/net/x25/x25_subr.c
index 8aa415a38814..8b1b06cabcbf 100644
--- a/net/x25/x25_subr.c
+++ b/net/x25/x25_subr.c
@@ -357,6 +357,10 @@ void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
 		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);
 }
 
 /*
-- 
2.7.4