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

Nicolas Dichtel
2014-01-30T10:09:21Z

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 <nicolas.dichtel@6wind.com>
Acked-by: Willem de Bruijn <willemb@google.com>
---
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