l2tp: fix a sock refcnt leak in l2tp_tunnel_register

[ Upstream commit f8504f4ca0a0e9f84546ef86e00b24d2ea9a0bd2 ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 82cdf90..26f1d43 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1490,12 +1490,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
                        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);
@@ -1510,6 +1505,10 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
        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) {
                struct udp_tunnel_sock_cfg udp_cfg = {
                        .sk_user_data = tunnel,