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    Subject[PATCH 4.9 066/105] l2tp: fix race condition in l2tp_tunnel_delete
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Sabrina Dubroca <sd@queasysnail.net>


    [ 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@redhat.com>
    Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
    Acked-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>
    ---
    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
    @@ -1737,14 +1737,12 @@ 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];
    @@ -257,7 +260,7 @@ 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,

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