[PATCH 3.16 139/366] l2tp: fix race in duplicate tunnel detection

Ben Hutchings
2018-10-14T15:25:41Z

From: Guillaume Nault <g.nault@alphalink.fr>

commit f6cd651b056ffd3b4e8496afd44d4ed44bf69136 upstream.

We can't use l2tp_tunnel_find() to prevent l2tp_nl_cmd_tunnel_create()
from creating a duplicate tunnel. A tunnel can be concurrently
registered after l2tp_tunnel_find() returns. Therefore, searching for
duplicates must be done at registration time.

Finally, remove l2tp_tunnel_find() entirely as it isn't use anywhere
anymore.

Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/l2tp/l2tp_core.c | 35 ++++++++++++++---------------------
net/l2tp/l2tp_core.h | 1 -
net/l2tp/l2tp_netlink.c | 6 ------
3 files changed, 14 insertions(+), 28 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -395,26 +395,6 @@ err_tlock:
}
EXPORT_SYMBOL_GPL(l2tp_session_register);

-/* Lookup a tunnel by id
- */
-struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id)
-{
- struct l2tp_tunnel *tunnel;
- struct l2tp_net *pn = l2tp_pernet(net);
-
- rcu_read_lock_bh();
- list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
- if (tunnel->tunnel_id == tunnel_id) {
- rcu_read_unlock_bh();
- return tunnel;
- }
- }
- rcu_read_unlock_bh();
-
- return NULL;
-}
-EXPORT_SYMBOL_GPL(l2tp_tunnel_find);
-
struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth)
{
struct l2tp_net *pn = l2tp_pernet(net);
@@ -1625,6 +1605,7 @@ static int l2tp_validate_socket(const st
int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
struct l2tp_tunnel_cfg *cfg)
{
+ struct l2tp_tunnel *tunnel_walk;
struct l2tp_net *pn;
struct socket *sock;
struct sock *sk;
@@ -1653,7 +1634,16 @@ int l2tp_tunnel_register(struct l2tp_tun
tunnel->l2tp_net = net;

pn = l2tp_pernet(net);
+
spin_lock_bh(&pn->l2tp_tunnel_list_lock);
+ list_for_each_entry(tunnel_walk, &pn->l2tp_tunnel_list, list) {
+ if (tunnel_walk->tunnel_id == tunnel->tunnel_id) {
+ spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
+
+ ret = -EEXIST;
+ goto err_sock;
+ }
+ }
list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
spin_unlock_bh(&pn->l2tp_tunnel_list_lock);

@@ -1683,7 +1673,10 @@ int l2tp_tunnel_register(struct l2tp_tun
return 0;

err_sock:
- sockfd_put(sock);
+ if (tunnel->fd < 0)
+ sock_release(sock);
+ else
+ sockfd_put(sock);
err:
return ret;
}
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -240,7 +240,6 @@ struct l2tp_session *l2tp_session_get_nt
struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
const char *ifname,
bool do_ref);
-struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id);
struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth);

int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id,
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -177,12 +177,6 @@ static int l2tp_nl_cmd_tunnel_create(str
if (info->attrs[L2TP_ATTR_DEBUG])
cfg.debug = nla_get_u32(info->attrs[L2TP_ATTR_DEBUG]);

- tunnel = l2tp_tunnel_find(net, tunnel_id);
- if (tunnel != NULL) {
- ret = -EEXIST;
- goto out;
- }
-
ret = -EINVAL;
switch (cfg.encap) {
case L2TP_ENCAPTYPE_UDP: