This is a note to let you know that I've just added the patch titled l2tp: fix race condition in l2tp_tunnel_delete to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: l2tp-fix-race-condition-in-l2tp_tunnel_delete.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Thu Oct 19 14:05:19 CEST 2017 From: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx> Date: Tue, 26 Sep 2017 16:16:43 +0200 Subject: l2tp: fix race condition in l2tp_tunnel_delete From: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx> [ Upstream commit 62b982eeb4589b2e6d7c01a90590e3a4c2b2ca19 ] If we try to delete the same tunnel twice, 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 to prevent firing the workqueue twice. 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 <jishi@xxxxxxxxxx> Signed-off-by: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx> Acked-by: Guillaume Nault <g.nault@xxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/l2tp/l2tp_core.c | 10 ++++------ net/l2tp/l2tp_core.h | 5 ++++- 2 files changed, 8 insertions(+), 7 deletions(-) --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1643,14 +1643,12 @@ 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) { - l2tp_tunnel_inc_refcount(tunnel); - if (false == queue_work(l2tp_wq, &tunnel->del_work)) { - l2tp_tunnel_dec_refcount(tunnel); - return 1; + if (!test_and_set_bit(0, &tunnel->dead)) { + l2tp_tunnel_inc_refcount(tunnel); + queue_work(l2tp_wq, &tunnel->del_work); } - return 0; } EXPORT_SYMBOL_GPL(l2tp_tunnel_delete); --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -169,6 +169,9 @@ struct l2tp_tunnel_cfg { struct l2tp_tunnel { int magic; /* Should be L2TP_TUNNEL_MAGIC */ + + unsigned long dead; + struct rcu_head rcu; rwlock_t hlist_lock; /* protect session_hlist */ struct hlist_head session_hlist[L2TP_HASH_SIZE]; @@ -253,7 +256,7 @@ int l2tp_tunnel_create(struct net *net, 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, Patches currently in stable-queue which might be from sd@xxxxxxxxxxxxxxx are queue-4.4/l2tp-fix-race-condition-in-l2tp_tunnel_delete.patch