From d101450583c3a472a2a94904cfe13fd4e7d2f519 Mon Sep 17 00:00:00 2001
From: Nicolas Dichtel <redacted>
Date: Wed, 29 Jan 2014 16:40:30 +0100
Subject: [PATCH] sit: fix double free of fb_tunnel_dev on exit

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().

CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Nicolas Dichtel <redacted>
---
 net/ipv6/sit.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 0491264b8bfc..620d326e8fdd 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c

@@ -1507,6 +1507,15 @@ static const struct nla_policy ipip6_policy[IFLA_IPTUN_MAX + 1] = {
 #endif
 };

+static void ipip6_dellink(struct net_device *dev, struct list_head *head)
+{
+       struct net *net = dev_net(dev);
+       struct sit_net *sitn = net_generic(net, sit_net_id);
+
+       if (dev != sitn->fb_tunnel_dev)
+               unregister_netdevice_queue(dev, head);
+}
+
 static struct rtnl_link_ops sit_link_ops __read_mostly = {
        .kind           = "sit",
        .maxtype        = IFLA_IPTUN_MAX,

@@ -1517,6 +1526,7 @@ static struct rtnl_link_ops sit_link_ops __read_mostly = {
        .changelink     = ipip6_changelink,
        .get_size       = ipip6_get_size,
        .fill_info      = ipip6_fill_info,
+       .dellink        = ipip6_dellink,
 };

 static struct xfrm_tunnel sit_handler __read_mostly = {
--

1.8.4.1