l2tp: fix race condition in l2tp_tunnel_delete
authorSabrina Dubroca <sd@queasysnail.net>
Tue, 26 Sep 2017 14:16:43 +0000 (16:16 +0200)
committerDavid S. Miller <davem@davemloft.net>
Tue, 26 Sep 2017 17:24:34 +0000 (10:24 -0700)
commit62b982eeb4589b2e6d7c01a90590e3a4c2b2ca19
tree49dabd03d76177db735d196ecf9883191d6ac5cc
parent36f6ee22d2d66046e369757ec6bbe1c482957ba6
l2tp: fix race condition in l2tp_tunnel_delete

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>
net/l2tp/l2tp_core.c
net/l2tp/l2tp_core.h