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Subject[PATCH 3.16 203/305] l2tp: fix a sock refcnt leak in l2tp_tunnel_register
3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Xin Long <lucien.xin@gmail.com>

commit f8504f4ca0a0e9f84546ef86e00b24d2ea9a0bd2 upstream.

This issue happens when trying to add an existent tunnel. It
doesn't call sock_put() before returning -EEXIST to release
the sock refcnt that was held by calling sock_hold() before
the existence check.

This patch is to fix it by holding the sock after doing the
existence check.

Fixes: f6cd651b056f ("l2tp: fix race in duplicate tunnel detection")
Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/l2tp/l2tp_core.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1627,12 +1627,7 @@ int l2tp_tunnel_register(struct l2tp_tun
goto err_sock;
}

- sk = sock->sk;
-
- sock_hold(sk);
- tunnel->sock = sk;
tunnel->l2tp_net = net;
-
pn = l2tp_pernet(net);

spin_lock_bh(&pn->l2tp_tunnel_list_lock);
@@ -1647,6 +1642,10 @@ int l2tp_tunnel_register(struct l2tp_tun
list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
spin_unlock_bh(&pn->l2tp_tunnel_list_lock);

+ sk = sock->sk;
+ sock_hold(sk);
+ tunnel->sock = sk;
+
if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
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