The tunnel is currently removed from the list during destruction. This
can lead to a double-free of the struct sock if we try to delete the tunnel
twice fast enough.
The first delete operation does a lookup (l2tp_tunnel_get), finds the
tunnel, calls l2tp_tunnel_delete, which queues it for deletion by
l2tp_tunnel_del_work.
The second delete operation also finds the tunnel and calls
l2tp_tunnel_delete. If the workqueue has already fired and started
running l2tp_tunnel_del_work, then l2tp_tunnel_delete will queue the
same tunnel a second time, and try to free the socket again.
Add a dead flag and remove tunnel from its list earlier. Then we can
remove the check of queue_work's result that was meant to prevent that
race but doesn't.
Reproducer:
ip l2tp add tunnel tunnel_id 3000 peer_tunnel_id 4000 local 192.168.0.2
remote 192.168.0.1 encap udp udp_sport 5000 udp_dport 6000
ip l2tp add session name l2tp1 tunnel_id 3000 session_id 1000
peer_session_id 2000
ip link set l2tp1 up
ip l2tp del tunnel tunnel_id 3000
ip l2tp del tunnel tunnel_id 3000
Fixes: f8ccac0e4493 ("l2tp: put tunnel socket release on a workqueue")
Reported-by: Jianlin Shi <ji...@redhat.com>
Signed-off-by: Sabrina Dubroca <s...@queasysnail.net>
---
net/l2tp/l2tp_core.c | 30 ++++++++++++++++--------------
net/l2tp/l2tp_core.h | 4 +++-
2 files changed, 19 insertions(+), 15 deletions(-)
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index ee485df73ccd..26553d3c4f8f 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1245,7 +1245,6 @@ EXPORT_SYMBOL_GPL(l2tp_xmit_skb);
static void l2tp_tunnel_destruct(struct sock *sk)
{
struct l2tp_tunnel *tunnel = l2tp_tunnel(sk);
- struct l2tp_net *pn;
if (tunnel == NULL)
goto end;
@@ -1269,13 +1268,6 @@ static void l2tp_tunnel_destruct(struct sock *sk)
sk->sk_destruct = tunnel->old_sk_destruct;
sk->sk_user_data = NULL;
- /* Remove the tunnel struct from the tunnel list */
- pn = l2tp_pernet(tunnel->l2tp_net);
- spin_lock_bh(&pn->l2tp_tunnel_list_lock);
- list_del_rcu(&tunnel->list);
- spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
- atomic_dec(&l2tp_tunnel_count);
-
l2tp_tunnel_closeall(tunnel);
tunnel->sock = NULL;
@@ -1685,14 +1677,24 @@ EXPORT_SYMBOL_GPL(l2tp_tunnel_create);
/* This function is used by the netlink TUNNEL_DELETE command.
*/
-int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
+void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
{
+ struct l2tp_net *pn;
+
+ if (tunnel->dead)
+ return;
+
l2tp_tunnel_inc_refcount(tunnel);
- if (false == queue_work(l2tp_wq, &tunnel->del_work)) {
- l2tp_tunnel_dec_refcount(tunnel);
- return 1;
- }
- return 0;
+
+ /* Remove the tunnel struct from the tunnel list */
+ pn = l2tp_pernet(tunnel->l2tp_net);
+ spin_lock_bh(&pn->l2tp_tunnel_list_lock);
+ tunnel->dead = 1;
+ list_del_rcu(&tunnel->list);
+ spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
+ atomic_dec(&l2tp_tunnel_count);
+
+ queue_work(l2tp_wq, &tunnel->del_work);
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index a305e0c5925a..173e68bb8119 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -160,6 +160,8 @@ struct l2tp_tunnel_cfg {
struct l2tp_tunnel {
int magic; /* Should be L2TP_TUNNEL_MAGIC
*/
+ int dead;
+
struct rcu_head rcu;
rwlock_t hlist_lock; /* protect session_hlist */
bool acpt_newsess; /* Indicates whether this
@@ -254,7 +256,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int
version, u32 tunnel_id,
u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
struct l2tp_tunnel **tunnelp);
void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel);
-int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);
+void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);
struct l2tp_session *l2tp_session_create(int priv_size,
struct l2tp_tunnel *tunnel,
u32 session_id, u32 peer_session_id,
--
2.14.1
