[PATCH 2/2] sit: fix use after free of fb_tunnel_dev

Steven Rostedt
2014-01-28T21:05:45Z

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From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 9434266f2c645d4fcf62a03a8e36ad8075e37943 ]

Bug: The fallback device is created in sit_init_net and assumed to be
freed in sit_exit_net. First, it is dereferenced in that function, in
sit_destroy_tunnels:

struct net *net = dev_net(sitn->fb_tunnel_dev);

Prior to this, rtnl_unlink_register has removed all devices that match
rtnl_link_ops == sit_link_ops.

Commit 205983c43700 added the line

+ sitn->fb_tunnel_dev->rtnl_link_ops = &sit_link_ops;

which cases the fallback device to match here and be freed before it
is last dereferenced.

Fix: This commit adds an explicit .delllink callback to sit_link_ops
that skips deallocation at rtnl_unlink_register for the fallback
device. This mechanism is comparable to the one in ip_tunnel.

It also modifies sit_destroy_tunnels and its only caller sit_exit_net
to avoid the offending dereference in the first place. That double
lookup is more complicated than required.

Test: The bug is only triggered when CONFIG_NET_NS is enabled. It
causes a GPF only when CONFIG_DEBUG_SLAB is enabled. Verified that
this bug exists at the mentioned commit, at davem-net HEAD and at
3.11.y HEAD. Verified that it went away after applying this patch.

Fixes: 205983c43700 ("sit: allow to use rtnl ops on fb tunnel")

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
net/ipv6/sit.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 3652033..d80055a 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 = {
@@ -1525,8 +1535,11 @@ static struct xfrm_tunnel sit_handler __read_mostly = {
.priority = 1,
};

-static void __net_exit sit_destroy_tunnels(struct sit_net *sitn, struct list_head *head)
+static void __net_exit sit_destroy_tunnels(struct net *net,
+ struct list_head *head)
{
+ struct sit_net *sitn = net_generic(net, sit_net_id);
+ struct net_device *dev, *aux;
int prio;

for_each_netdev_safe(net, dev, aux)
@@ -1596,12 +1609,10 @@ err_alloc_dev:

static void __net_exit sit_exit_net(struct net *net)
{
- struct sit_net *sitn = net_generic(net, sit_net_id);
LIST_HEAD(list);

rtnl_lock();
- sit_destroy_tunnels(sitn, &list);
- unregister_netdevice_queue(sitn->fb_tunnel_dev, &list);
+ sit_destroy_tunnels(net, &list);
unregister_netdevice_many(&list);
rtnl_unlock();
}
--
1.8.4.3