l2tp: fix use-after-free during module unload
BugLink: https://bugs.launchpad.net/bugs/1878232 commit 2f86953e upstream. Tunnel deletion is delayed by both a workqueue (l2tp_tunnel_delete -> wq -> l2tp_tunnel_del_work) and RCU (sk_destruct -> RCU -> l2tp_tunnel_destruct). By the time l2tp_tunnel_destruct() runs to destroy the tunnel and finish destroying the socket, the private data reserved via the net_generic mechanism has already been freed, but l2tp_tunnel_destruct() actually uses this data. Make sure tunnel deletion for the netns has completed before returning from l2tp_exit_net() by first flushing the tunnel removal workqueue, and then waiting for RCU callbacks to complete. Fixes: 167eb17e ("l2tp: create tunnel sockets in the right namespace") Signed-off-by: Sabrina Dubroca <sd@queasysnail.net> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Ian May <ian.may@canonical.com> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
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