From 9434266f2c645d4fcf62a03a8e36ad8075e37943 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Wed, 13 Nov 2013 21:27:38 -0500 Subject: [PATCH] sit: fix use after free of fb_tunnel_dev 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 Acked-by: Nicolas Dichtel Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv6/sit.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c index 3a9038dd818d..5a57f38a50d5 100644 --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -1604,6 +1604,15 @@ 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, @@ -1615,6 +1624,7 @@ 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 = { @@ -1629,9 +1639,10 @@ static struct xfrm_tunnel ipip_handler __read_mostly = { .priority = 2, }; -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 net *net = dev_net(sitn->fb_tunnel_dev); + struct sit_net *sitn = net_generic(net, sit_net_id); struct net_device *dev, *aux; int prio; @@ -1706,11 +1717,10 @@ 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); + sit_destroy_tunnels(net, &list); unregister_netdevice_many(&list); rtnl_unlock(); } -- 2.20.1