Re: [PATCH linux-3.10.y v2 1/3] sit: fix double free of fb_tunnel_dev on exit

Just FYI.

Our full tier tests have completed with no issues due to the sit or
ip6_tunnel modules. These patches appear to have solved our problems.

Nicolas, Thanks again for posting these!

-- Steve


On Fri, 31 Jan 2014 09:24:04 +0100
Nicolas Dichtel [off-list ref] wrote:

This problem was fixed upstream by commit 9434266f2c64 ("sit: fix use after free
of fb_tunnel_dev").
The upstream patch depends on upstream commit 5e6700b3bf98 ("sit: add support of
x-netns"), which was not backported into 3.10 branch.

First, explain the problem: when the sit module is unloaded, sit_cleanup() is
called.
rmmod sit
=> sit_cleanup()
  => rtnl_link_unregister()
    => __rtnl_kill_links()
      => for_each_netdev(net, dev) {
        if (dev->rtnl_link_ops == ops)
        	ops->dellink(dev, &list_kill);
        }
At this point, the FB device is deleted (and all sit tunnels).
  => unregister_pernet_device()
    => unregister_pernet_operations()
      => ops_exit_list()
        => sit_exit_net()
          => sit_destroy_tunnels()
          In this function, no tunnel is found.
          => unregister_netdevice_queue(sitn->fb_tunnel_dev, &list);
We delete the FB device a second time here!

Because we cannot simply remove the second deletion (sit_exit_net() must remove
the FB device when a netns is deleted), we add an rtnl ops which delete all sit
device excepting the FB device and thus we can keep the explicit deletion in
sit_exit_net().