releases/4.13.6/l2tp-fix-race-condition-in-l2tp_tunnel_delete.patch

   1 From foo@baz Mon Oct  9 09:32:35 CEST 2017
   2 From: Sabrina Dubroca <sd@queasysnail.net>
   3 Date: Tue, 26 Sep 2017 16:16:43 +0200
   4 Subject: l2tp: fix race condition in l2tp_tunnel_delete
   5
   6 From: Sabrina Dubroca <sd@queasysnail.net>
   7
   8
   9 [ Upstream commit 62b982eeb4589b2e6d7c01a90590e3a4c2b2ca19 ]
  10
  11 If we try to delete the same tunnel twice, the first delete operation
  12 does a lookup (l2tp_tunnel_get), finds the tunnel, calls
  13 l2tp_tunnel_delete, which queues it for deletion by
  14 l2tp_tunnel_del_work.
  15
  16 The second delete operation also finds the tunnel and calls
  17 l2tp_tunnel_delete. If the workqueue has already fired and started
  18 running l2tp_tunnel_del_work, then l2tp_tunnel_delete will queue the
  19 same tunnel a second time, and try to free the socket again.
  20
  21 Add a dead flag to prevent firing the workqueue twice. Then we can
  22 remove the check of queue_work's result that was meant to prevent that
  23 race but doesn't.
  24
  25 Reproducer:
  26
  27     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
  28     ip l2tp add session name l2tp1 tunnel_id 3000 session_id 1000 peer_session_id 2000
  29     ip link set l2tp1 up
  30     ip l2tp del tunnel tunnel_id 3000
  31     ip l2tp del tunnel tunnel_id 3000
  32
  33 Fixes: f8ccac0e4493 ("l2tp: put tunnel socket release on a workqueue")
  34 Reported-by: Jianlin Shi <jishi@redhat.com>
  35 Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
  36 Acked-by: Guillaume Nault <g.nault@alphalink.fr>
  37 Signed-off-by: David S. Miller <davem@davemloft.net>
  38 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  39 ---
  40  net/l2tp/l2tp_core.c |   10 ++++------
  41  net/l2tp/l2tp_core.h |    5 ++++-
  42  2 files changed, 8 insertions(+), 7 deletions(-)
  43
  44 --- a/net/l2tp/l2tp_core.c
  45 +++ b/net/l2tp/l2tp_core.c
  46 @@ -1665,14 +1665,12 @@ EXPORT_SYMBOL_GPL(l2tp_tunnel_create);
  47
  48  /* This function is used by the netlink TUNNEL_DELETE command.
  49   */
  50 -int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
  51 +void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
  52  {
  53 -       l2tp_tunnel_inc_refcount(tunnel);
  54 -       if (false == queue_work(l2tp_wq, &tunnel->del_work)) {
  55 -               l2tp_tunnel_dec_refcount(tunnel);
  56 -               return 1;
  57 +       if (!test_and_set_bit(0, &tunnel->dead)) {
  58 +               l2tp_tunnel_inc_refcount(tunnel);
  59 +               queue_work(l2tp_wq, &tunnel->del_work);
  60         }
  61 -       return 0;
  62  }
  63  EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);
  64
  65 --- a/net/l2tp/l2tp_core.h
  66 +++ b/net/l2tp/l2tp_core.h
  67 @@ -160,6 +160,9 @@ struct l2tp_tunnel_cfg {
  68
  69  struct l2tp_tunnel {
  70         int                     magic;          /* Should be L2TP_TUNNEL_MAGIC */
  71 +
  72 +       unsigned long           dead;
  73 +
  74         struct rcu_head rcu;
  75         rwlock_t                hlist_lock;     /* protect session_hlist */
  76         struct hlist_head       session_hlist[L2TP_HASH_SIZE];
  77 @@ -248,7 +251,7 @@ int l2tp_tunnel_create(struct net *net,
  78                        u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
  79                        struct l2tp_tunnel **tunnelp);
  80  void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel);
  81 -int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);
  82 +void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);
  83  struct l2tp_session *l2tp_session_create(int priv_size,
  84                                          struct l2tp_tunnel *tunnel,
  85                                          u32 session_id, u32 peer_session_id,