path: root/net/netfilter
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authorPablo Neira Ayuso <pablo@netfilter.org>2015-07-13 15:11:48 +0200
committerPablo Neira Ayuso <pablo@netfilter.org>2015-07-20 14:58:19 +0200
commit0838aa7fcfcd875caa7bcc5dab0c3fd40444553d (patch)
tree6487656be1e71eebff5a6612c09558f82a0e07e0 /net/netfilter
parent484836ec2de24d9a7c6471f022b746d947698725 (diff)
netfilter: fix netns dependencies with conntrack templates
Quoting Daniel Borkmann: "When adding connection tracking template rules to a netns, f.e. to configure netfilter zones, the kernel will endlessly busy-loop as soon as we try to delete the given netns in case there's at least one template present, which is problematic i.e. if there is such bravery that the priviledged user inside the netns is assumed untrusted. Minimal example: ip netns add foo ip netns exec foo iptables -t raw -A PREROUTING -d -j CT --zone 1 ip netns del foo What happens is that when nf_ct_iterate_cleanup() is being called from nf_conntrack_cleanup_net_list() for a provided netns, we always end up with a net->ct.count > 0 and thus jump back to i_see_dead_people. We don't get a soft-lockup as we still have a schedule() point, but the serving CPU spins on 100% from that point onwards. Since templates are normally allocated with nf_conntrack_alloc(), we also bump net->ct.count. The issue why they are not yet nf_ct_put() is because the per netns .exit() handler from x_tables (which would eventually invoke xt_CT's xt_ct_tg_destroy() that drops reference on info->ct) is called in the dependency chain at a *later* point in time than the per netns .exit() handler for the connection tracker. This is clearly a chicken'n'egg problem: after the connection tracker .exit() handler, we've teared down all the connection tracking infrastructure already, so rightfully, xt_ct_tg_destroy() cannot be invoked at a later point in time during the netns cleanup, as that would lead to a use-after-free. At the same time, we cannot make x_tables depend on the connection tracker module, so that the xt_ct_tg_destroy() would be invoked earlier in the cleanup chain." Daniel confirms this has to do with the order in which modules are loaded or having compiled nf_conntrack as modules while x_tables built-in. So we have no guarantees regarding the order in which netns callbacks are executed. Fix this by allocating the templates through kmalloc() from the respective SYNPROXY and CT targets, so they don't depend on the conntrack kmem cache. Then, release then via nf_ct_tmpl_free() from destroy_conntrack(). This branch is marked as unlikely since conntrack templates are rarely allocated and only from the configuration plane path. Note that templates are not kept in any list to avoid further dependencies with nf_conntrack anymore, thus, the tmpl larval list is removed. Reported-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Tested-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'net/netfilter')
3 files changed, 50 insertions, 32 deletions
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 13fad8668f83..651039ad1681 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -287,6 +287,46 @@ static void nf_ct_del_from_dying_or_unconfirmed_list(struct nf_conn *ct)
+/* Released via destroy_conntrack() */
+struct nf_conn *nf_ct_tmpl_alloc(struct net *net, u16 zone, gfp_t flags)
+ struct nf_conn *tmpl;
+ tmpl = kzalloc(sizeof(struct nf_conn), GFP_KERNEL);
+ if (tmpl == NULL)
+ return NULL;
+ tmpl->status = IPS_TEMPLATE;
+ write_pnet(&tmpl->ct_net, net);
+ if (zone) {
+ struct nf_conntrack_zone *nf_ct_zone;
+ nf_ct_zone = nf_ct_ext_add(tmpl, NF_CT_EXT_ZONE, GFP_ATOMIC);
+ if (!nf_ct_zone)
+ goto out_free;
+ nf_ct_zone->id = zone;
+ }
+ atomic_set(&tmpl->ct_general.use, 0);
+ return tmpl;
+ kfree(tmpl);
+ return NULL;
+static void nf_ct_tmpl_free(struct nf_conn *tmpl)
+ nf_ct_ext_destroy(tmpl);
+ nf_ct_ext_free(tmpl);
+ kfree(tmpl);
static void
destroy_conntrack(struct nf_conntrack *nfct)
@@ -298,6 +338,10 @@ destroy_conntrack(struct nf_conntrack *nfct)
NF_CT_ASSERT(atomic_read(&nfct->use) == 0);
+ if (unlikely(nf_ct_is_template(ct))) {
+ nf_ct_tmpl_free(ct);
+ return;
+ }
l4proto = __nf_ct_l4proto_find(nf_ct_l3num(ct), nf_ct_protonum(ct));
if (l4proto && l4proto->destroy)
@@ -540,28 +584,6 @@ out:
-/* deletion from this larval template list happens via nf_ct_put() */
-void nf_conntrack_tmpl_insert(struct net *net, struct nf_conn *tmpl)
- struct ct_pcpu *pcpu;
- __set_bit(IPS_TEMPLATE_BIT, &tmpl->status);
- __set_bit(IPS_CONFIRMED_BIT, &tmpl->status);
- nf_conntrack_get(&tmpl->ct_general);
- /* add this conntrack to the (per cpu) tmpl list */
- local_bh_disable();
- tmpl->cpu = smp_processor_id();
- pcpu = per_cpu_ptr(nf_ct_net(tmpl)->ct.pcpu_lists, tmpl->cpu);
- spin_lock(&pcpu->lock);
- /* Overload tuple linked list to put us in template list. */
- hlist_nulls_add_head_rcu(&tmpl->tuplehash[IP_CT_DIR_ORIGINAL].hnnode,
- &pcpu->tmpl);
- spin_unlock_bh(&pcpu->lock);
/* Confirm a connection given skb; places it in hash table */
__nf_conntrack_confirm(struct sk_buff *skb)
@@ -1751,7 +1773,6 @@ int nf_conntrack_init_net(struct net *net)
net->ct.stat = alloc_percpu(struct ip_conntrack_stat);
diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index 789feeae6c44..71f1e9fdfa18 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -349,12 +349,10 @@ static void __net_exit synproxy_proc_exit(struct net *net)
static int __net_init synproxy_net_init(struct net *net)
struct synproxy_net *snet = synproxy_pernet(net);
- struct nf_conntrack_tuple t;
struct nf_conn *ct;
int err = -ENOMEM;
- memset(&t, 0, sizeof(t));
- ct = nf_conntrack_alloc(net, 0, &t, &t, GFP_KERNEL);
+ ct = nf_ct_tmpl_alloc(net, 0, GFP_KERNEL);
if (IS_ERR(ct)) {
err = PTR_ERR(ct);
goto err1;
@@ -365,7 +363,8 @@ static int __net_init synproxy_net_init(struct net *net)
if (!nfct_synproxy_ext_add(ct))
goto err2;
- nf_conntrack_tmpl_insert(net, ct);
+ __set_bit(IPS_CONFIRMED_BIT, &ct->status);
+ nf_conntrack_get(&ct->ct_general);
snet->tmpl = ct;
snet->stats = alloc_percpu(struct synproxy_stats);
diff --git a/net/netfilter/xt_CT.c b/net/netfilter/xt_CT.c
index 75747aecdebe..c6630030c912 100644
--- a/net/netfilter/xt_CT.c
+++ b/net/netfilter/xt_CT.c
@@ -184,7 +184,6 @@ out:
static int xt_ct_tg_check(const struct xt_tgchk_param *par,
struct xt_ct_target_info_v1 *info)
- struct nf_conntrack_tuple t;
struct nf_conn *ct;
int ret = -EOPNOTSUPP;
@@ -202,8 +201,7 @@ static int xt_ct_tg_check(const struct xt_tgchk_param *par,
if (ret < 0)
goto err1;
- memset(&t, 0, sizeof(t));
- ct = nf_conntrack_alloc(par->net, info->zone, &t, &t, GFP_KERNEL);
+ ct = nf_ct_tmpl_alloc(par->net, info->zone, GFP_KERNEL);
ret = PTR_ERR(ct);
if (IS_ERR(ct))
goto err2;
@@ -227,8 +225,8 @@ static int xt_ct_tg_check(const struct xt_tgchk_param *par,
if (ret < 0)
goto err3;
- nf_conntrack_tmpl_insert(par->net, ct);
+ __set_bit(IPS_CONFIRMED_BIT, &ct->status);
+ nf_conntrack_get(&ct->ct_general);
info->ct = ct;
return 0;

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