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l2tp: fix race in duplicate tunnel detection

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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: 309795f4be ("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>
This commit is contained in:
Guillaume Nault 2018-04-10 21:01:13 +02:00 committed by David S. Miller
parent 6b9f34239b
commit f6cd651b05
3 changed files with 14 additions and 28 deletions
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35
net/l2tp/l2tp_core.c
View file

@ -335,26 +335,6 @@ int l2tp_session_register(struct l2tp_session *session,
}
EXPORT_SYMBOL_GPL(l2tp_session_register);
/* Lookup a tunnel by id
*/
struct l2tp_tunnel *l2tp_tunnel_find(const 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(const struct net *net, int nth)
{
struct l2tp_net *pn = l2tp_pernet(net);
@ -1501,6 +1481,7 @@ static int l2tp_validate_socket(const struct sock *sk, const struct net *net,
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;
@ -1529,7 +1510,16 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
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);
@ -1558,7 +1548,10 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
return 0;
err_sock:
sockfd_put(sock);
if (tunnel->fd < 0)
sock_release(sock);
else
sockfd_put(sock);
err:
return ret;
}

1
net/l2tp/l2tp_core.h
View file

@ -220,7 +220,6 @@ struct l2tp_session *l2tp_session_get(const struct net *net,
struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth);
struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
const char *ifname);
struct l2tp_tunnel *l2tp_tunnel_find(const struct net *net, u32 tunnel_id);
struct l2tp_tunnel *l2tp_tunnel_find_nth(const struct net *net, int nth);
int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id,

6
net/l2tp/l2tp_netlink.c
View file

@ -236,12 +236,6 @@ static int l2tp_nl_cmd_tunnel_create(struct sk_buff *skb, struct genl_info *info
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: