netfilter: add user-space connection tracking helper infrastructure
authorPablo Neira Ayuso <pablo@netfilter.org>
Sun, 13 May 2012 19:44:54 +0000 (21:44 +0200)
committerPablo Neira Ayuso <pablo@netfilter.org>
Sat, 16 Jun 2012 13:40:02 +0000 (15:40 +0200)
There are good reasons to supports helpers in user-space instead:

* Rapid connection tracking helper development, as developing code
  in user-space is usually faster.

* Reliability: A buggy helper does not crash the kernel. Moreover,
  we can monitor the helper process and restart it in case of problems.

* Security: Avoid complex string matching and mangling in kernel-space
  running in privileged mode. Going further, we can even think about
  running user-space helpers as a non-root process.

* Extensibility: It allows the development of very specific helpers (most
  likely non-standard proprietary protocols) that are very likely not to be
  accepted for mainline inclusion in the form of kernel-space connection
  tracking helpers.

This patch adds the infrastructure to allow the implementation of
user-space conntrack helpers by means of the new nfnetlink subsystem
`nfnetlink_cthelper' and the existing queueing infrastructure
(nfnetlink_queue).

I had to add the new hook NF_IP6_PRI_CONNTRACK_HELPER to register
ipv[4|6]_helper which results from splitting ipv[4|6]_confirm into
two pieces. This change is required not to break NAT sequence
adjustment and conntrack confirmation for traffic that is enqueued
to our user-space conntrack helpers.

Basic operation, in a few steps:

1) Register user-space helper by means of `nfct':

 nfct helper add ftp inet tcp

 [ It must be a valid existing helper supported by conntrack-tools ]

2) Add rules to enable the FTP user-space helper which is
   used to track traffic going to TCP port 21.

For locally generated packets:

 iptables -I OUTPUT -t raw -p tcp --dport 21 -j CT --helper ftp

For non-locally generated packets:

 iptables -I PREROUTING -t raw -p tcp --dport 21 -j CT --helper ftp

3) Run the test conntrackd in helper mode (see example files under
   doc/helper/conntrackd.conf

 conntrackd

4) Generate FTP traffic going, if everything is OK, then conntrackd
   should create expectations (you can check that with `conntrack':

 conntrack -E expect

    [NEW] 301 proto=6 src=192.168.1.136 dst=130.89.148.12 sport=0 dport=54037 mask-src=255.255.255.255 mask-dst=255.255.255.255 sport=0 dport=65535 master-src=192.168.1.136 master-dst=130.89.148.12 sport=57127 dport=21 class=0 helper=ftp
[DESTROY] 301 proto=6 src=192.168.1.136 dst=130.89.148.12 sport=0 dport=54037 mask-src=255.255.255.255 mask-dst=255.255.255.255 sport=0 dport=65535 master-src=192.168.1.136 master-dst=130.89.148.12 sport=57127 dport=21 class=0 helper=ftp

This confirms that our test helper is receiving packets including the
conntrack information, and adding expectations in kernel-space.

The user-space helper can also store its private tracking information
in the conntrack structure in the kernel via the CTA_HELP_INFO. The
kernel will consider this a binary blob whose layout is unknown. This
information will be included in the information that is transfered
to user-space via glue code that integrates nfnetlink_queue and
ctnetlink.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
12 files changed:
include/linux/netfilter/Kbuild
include/linux/netfilter/nfnetlink.h
include/linux/netfilter/nfnetlink_cthelper.h [new file with mode: 0644]
include/linux/netfilter_ipv4.h
include/linux/netfilter_ipv6.h
include/net/netfilter/nf_conntrack_helper.h
net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
net/netfilter/Kconfig
net/netfilter/Makefile
net/netfilter/nf_conntrack_helper.c
net/netfilter/nfnetlink_cthelper.c [new file with mode: 0644]

index 1697036336b6623a474212ebf8e4eeda4d4dc752..874ae8f2706b16572654faee8b1db74cab84a2bf 100644 (file)
@@ -10,6 +10,7 @@ header-y += nfnetlink.h
 header-y += nfnetlink_acct.h
 header-y += nfnetlink_compat.h
 header-y += nfnetlink_conntrack.h
+header-y += nfnetlink_cthelper.h
 header-y += nfnetlink_cttimeout.h
 header-y += nfnetlink_log.h
 header-y += nfnetlink_queue.h
index a1048c1587d1e36910ef78ea74c396577caa1a78..18341cdb2443816f5e3af91e0d42d49a57cb36ad 100644 (file)
@@ -50,7 +50,8 @@ struct nfgenmsg {
 #define NFNL_SUBSYS_IPSET              6
 #define NFNL_SUBSYS_ACCT               7
 #define NFNL_SUBSYS_CTNETLINK_TIMEOUT  8
-#define NFNL_SUBSYS_COUNT              9
+#define NFNL_SUBSYS_CTHELPER           9
+#define NFNL_SUBSYS_COUNT              10
 
 #ifdef __KERNEL__
 
diff --git a/include/linux/netfilter/nfnetlink_cthelper.h b/include/linux/netfilter/nfnetlink_cthelper.h
new file mode 100644 (file)
index 0000000..33659f6
--- /dev/null
@@ -0,0 +1,55 @@
+#ifndef _NFNL_CTHELPER_H_
+#define _NFNL_CTHELPER_H_
+
+#define NFCT_HELPER_STATUS_DISABLED    0
+#define NFCT_HELPER_STATUS_ENABLED     1
+
+enum nfnl_acct_msg_types {
+       NFNL_MSG_CTHELPER_NEW,
+       NFNL_MSG_CTHELPER_GET,
+       NFNL_MSG_CTHELPER_DEL,
+       NFNL_MSG_CTHELPER_MAX
+};
+
+enum nfnl_cthelper_type {
+       NFCTH_UNSPEC,
+       NFCTH_NAME,
+       NFCTH_TUPLE,
+       NFCTH_QUEUE_NUM,
+       NFCTH_POLICY,
+       NFCTH_PRIV_DATA_LEN,
+       NFCTH_STATUS,
+       __NFCTH_MAX
+};
+#define NFCTH_MAX (__NFCTH_MAX - 1)
+
+enum nfnl_cthelper_policy_type {
+       NFCTH_POLICY_SET_UNSPEC,
+       NFCTH_POLICY_SET_NUM,
+       NFCTH_POLICY_SET,
+       NFCTH_POLICY_SET1       = NFCTH_POLICY_SET,
+       NFCTH_POLICY_SET2,
+       NFCTH_POLICY_SET3,
+       NFCTH_POLICY_SET4,
+       __NFCTH_POLICY_SET_MAX
+};
+#define NFCTH_POLICY_SET_MAX (__NFCTH_POLICY_SET_MAX - 1)
+
+enum nfnl_cthelper_pol_type {
+       NFCTH_POLICY_UNSPEC,
+       NFCTH_POLICY_NAME,
+       NFCTH_POLICY_EXPECT_MAX,
+       NFCTH_POLICY_EXPECT_TIMEOUT,
+       __NFCTH_POLICY_MAX
+};
+#define NFCTH_POLICY_MAX (__NFCTH_POLICY_MAX - 1)
+
+enum nfnl_cthelper_tuple_type {
+       NFCTH_TUPLE_UNSPEC,
+       NFCTH_TUPLE_L3PROTONUM,
+       NFCTH_TUPLE_L4PROTONUM,
+       __NFCTH_TUPLE_MAX,
+};
+#define NFCTH_TUPLE_MAX (__NFCTH_TUPLE_MAX - 1)
+
+#endif /* _NFNL_CTHELPER_H */
index fa0946c549d3e874fb52324a3a4db20e41a7b67b..e2b12801378d8bd2e239a9516aea967328fe7ca4 100644 (file)
@@ -66,6 +66,7 @@ enum nf_ip_hook_priorities {
        NF_IP_PRI_SECURITY = 50,
        NF_IP_PRI_NAT_SRC = 100,
        NF_IP_PRI_SELINUX_LAST = 225,
+       NF_IP_PRI_CONNTRACK_HELPER = 300,
        NF_IP_PRI_CONNTRACK_CONFIRM = INT_MAX,
        NF_IP_PRI_LAST = INT_MAX,
 };
index 57c025127f1d48fb9447cec9ee38381532d3a29d..7c8a513ce7a3ed03f0612e972537deb6569339e8 100644 (file)
@@ -71,6 +71,7 @@ enum nf_ip6_hook_priorities {
        NF_IP6_PRI_SECURITY = 50,
        NF_IP6_PRI_NAT_SRC = 100,
        NF_IP6_PRI_SELINUX_LAST = 225,
+       NF_IP6_PRI_CONNTRACK_HELPER = 300,
        NF_IP6_PRI_LAST = INT_MAX,
 };
 
index 84b24c3a3834ee3701e1066314ef297ff2820aef..9aad956d1008e2be1c0b6e55b7588098321c642d 100644 (file)
 
 struct module;
 
+enum nf_ct_helper_flags {
+       NF_CT_HELPER_F_USERSPACE        = (1 << 0),
+       NF_CT_HELPER_F_CONFIGURED       = (1 << 1),
+};
+
 #define NF_CT_HELPER_NAME_LEN  16
 
 struct nf_conntrack_helper {
@@ -42,6 +47,9 @@ struct nf_conntrack_helper {
        int (*from_nlattr)(struct nlattr *attr, struct nf_conn *ct);
        int (*to_nlattr)(struct sk_buff *skb, const struct nf_conn *ct);
        unsigned int expect_class_max;
+
+       unsigned int flags;
+       unsigned int queue_num;         /* For user-space helpers. */
 };
 
 extern struct nf_conntrack_helper *
@@ -96,4 +104,7 @@ nf_ct_helper_expectfn_find_by_name(const char *name);
 struct nf_ct_helper_expectfn *
 nf_ct_helper_expectfn_find_by_symbol(const void *symbol);
 
+extern struct hlist_head *nf_ct_helper_hash;
+extern unsigned int nf_ct_helper_hsize;
+
 #endif /*_NF_CONNTRACK_HELPER_H*/
index d79b961a8009b5d110489156fff920dfa89a26cb..e7ff2dcab6cec0fdd82cfb5ce804e172b67adc1f 100644 (file)
@@ -95,11 +95,11 @@ static int ipv4_get_l4proto(const struct sk_buff *skb, unsigned int nhoff,
        return NF_ACCEPT;
 }
 
-static unsigned int ipv4_confirm(unsigned int hooknum,
-                                struct sk_buff *skb,
-                                const struct net_device *in,
-                                const struct net_device *out,
-                                int (*okfn)(struct sk_buff *))
+static unsigned int ipv4_helper(unsigned int hooknum,
+                               struct sk_buff *skb,
+                               const struct net_device *in,
+                               const struct net_device *out,
+                               int (*okfn)(struct sk_buff *))
 {
        struct nf_conn *ct;
        enum ip_conntrack_info ctinfo;
@@ -110,24 +110,38 @@ static unsigned int ipv4_confirm(unsigned int hooknum,
        /* This is where we call the helper: as the packet goes out. */
        ct = nf_ct_get(skb, &ctinfo);
        if (!ct || ctinfo == IP_CT_RELATED_REPLY)
-               goto out;
+               return NF_ACCEPT;
 
        help = nfct_help(ct);
        if (!help)
-               goto out;
+               return NF_ACCEPT;
 
        /* rcu_read_lock()ed by nf_hook_slow */
        helper = rcu_dereference(help->helper);
        if (!helper)
-               goto out;
+               return NF_ACCEPT;
 
        ret = helper->help(skb, skb_network_offset(skb) + ip_hdrlen(skb),
                           ct, ctinfo);
-       if (ret != NF_ACCEPT) {
+       if (ret != NF_ACCEPT && (ret & NF_VERDICT_MASK) != NF_QUEUE) {
                nf_log_packet(NFPROTO_IPV4, hooknum, skb, in, out, NULL,
                              "nf_ct_%s: dropping packet", helper->name);
-               return ret;
        }
+       return ret;
+}
+
+static unsigned int ipv4_confirm(unsigned int hooknum,
+                                struct sk_buff *skb,
+                                const struct net_device *in,
+                                const struct net_device *out,
+                                int (*okfn)(struct sk_buff *))
+{
+       struct nf_conn *ct;
+       enum ip_conntrack_info ctinfo;
+
+       ct = nf_ct_get(skb, &ctinfo);
+       if (!ct || ctinfo == IP_CT_RELATED_REPLY)
+               goto out;
 
        /* adjust seqs for loopback traffic only in outgoing direction */
        if (test_bit(IPS_SEQ_ADJUST_BIT, &ct->status) &&
@@ -184,6 +198,13 @@ static struct nf_hook_ops ipv4_conntrack_ops[] __read_mostly = {
                .hooknum        = NF_INET_LOCAL_OUT,
                .priority       = NF_IP_PRI_CONNTRACK,
        },
+       {
+               .hook           = ipv4_helper,
+               .owner          = THIS_MODULE,
+               .pf             = NFPROTO_IPV4,
+               .hooknum        = NF_INET_POST_ROUTING,
+               .priority       = NF_IP_PRI_CONNTRACK_HELPER,
+       },
        {
                .hook           = ipv4_confirm,
                .owner          = THIS_MODULE,
@@ -191,6 +212,13 @@ static struct nf_hook_ops ipv4_conntrack_ops[] __read_mostly = {
                .hooknum        = NF_INET_POST_ROUTING,
                .priority       = NF_IP_PRI_CONNTRACK_CONFIRM,
        },
+       {
+               .hook           = ipv4_helper,
+               .owner          = THIS_MODULE,
+               .pf             = NFPROTO_IPV4,
+               .hooknum        = NF_INET_LOCAL_IN,
+               .priority       = NF_IP_PRI_CONNTRACK_HELPER,
+       },
        {
                .hook           = ipv4_confirm,
                .owner          = THIS_MODULE,
index fca10da80ea796e0c90c5392bd7ed1cc05bd05d7..4794f96cf2e01bfcd5cc858cc22f73b325dbc907 100644 (file)
@@ -143,11 +143,11 @@ static int ipv6_get_l4proto(const struct sk_buff *skb, unsigned int nhoff,
        return NF_ACCEPT;
 }
 
-static unsigned int ipv6_confirm(unsigned int hooknum,
-                                struct sk_buff *skb,
-                                const struct net_device *in,
-                                const struct net_device *out,
-                                int (*okfn)(struct sk_buff *))
+static unsigned int ipv6_helper(unsigned int hooknum,
+                               struct sk_buff *skb,
+                               const struct net_device *in,
+                               const struct net_device *out,
+                               int (*okfn)(struct sk_buff *))
 {
        struct nf_conn *ct;
        const struct nf_conn_help *help;
@@ -161,15 +161,15 @@ static unsigned int ipv6_confirm(unsigned int hooknum,
        /* This is where we call the helper: as the packet goes out. */
        ct = nf_ct_get(skb, &ctinfo);
        if (!ct || ctinfo == IP_CT_RELATED_REPLY)
-               goto out;
+               return NF_ACCEPT;
 
        help = nfct_help(ct);
        if (!help)
-               goto out;
+               return NF_ACCEPT;
        /* rcu_read_lock()ed by nf_hook_slow */
        helper = rcu_dereference(help->helper);
        if (!helper)
-               goto out;
+               return NF_ACCEPT;
 
        protoff = nf_ct_ipv6_skip_exthdr(skb, extoff, &pnum,
                                         skb->len - extoff);
@@ -179,12 +179,19 @@ static unsigned int ipv6_confirm(unsigned int hooknum,
        }
 
        ret = helper->help(skb, protoff, ct, ctinfo);
-       if (ret != NF_ACCEPT) {
+       if (ret != NF_ACCEPT && (ret & NF_VERDICT_MASK) != NF_QUEUE) {
                nf_log_packet(NFPROTO_IPV6, hooknum, skb, in, out, NULL,
                              "nf_ct_%s: dropping packet", helper->name);
-               return ret;
        }
-out:
+       return ret;
+}
+
+static unsigned int ipv6_confirm(unsigned int hooknum,
+                                struct sk_buff *skb,
+                                const struct net_device *in,
+                                const struct net_device *out,
+                                int (*okfn)(struct sk_buff *))
+{
        /* We've seen it coming out the other side: confirm it */
        return nf_conntrack_confirm(skb);
 }
@@ -253,6 +260,13 @@ static struct nf_hook_ops ipv6_conntrack_ops[] __read_mostly = {
                .hooknum        = NF_INET_LOCAL_OUT,
                .priority       = NF_IP6_PRI_CONNTRACK,
        },
+       {
+               .hook           = ipv6_helper,
+               .owner          = THIS_MODULE,
+               .pf             = NFPROTO_IPV6,
+               .hooknum        = NF_INET_POST_ROUTING,
+               .priority       = NF_IP6_PRI_CONNTRACK_HELPER,
+       },
        {
                .hook           = ipv6_confirm,
                .owner          = THIS_MODULE,
@@ -260,6 +274,13 @@ static struct nf_hook_ops ipv6_conntrack_ops[] __read_mostly = {
                .hooknum        = NF_INET_POST_ROUTING,
                .priority       = NF_IP6_PRI_LAST,
        },
+       {
+               .hook           = ipv6_helper,
+               .owner          = THIS_MODULE,
+               .pf             = NFPROTO_IPV6,
+               .hooknum        = NF_INET_LOCAL_IN,
+               .priority       = NF_IP6_PRI_CONNTRACK_HELPER,
+       },
        {
                .hook           = ipv6_confirm,
                .owner          = THIS_MODULE,
index 209c1ed43368ed4460c865541aa3cb149963710e..aae6c628991dd8f172bc93357769e61ecdd39c8a 100644 (file)
@@ -12,6 +12,14 @@ tristate "Netfilter NFACCT over NFNETLINK interface"
          If this option is enabled, the kernel will include support
          for extended accounting via NFNETLINK.
 
+config NETFILTER_NETLINK_CTHELPER
+tristate "Netfilter CTHELPER over NFNETLINK interface"
+       depends on NETFILTER_ADVANCED
+       select NETFILTER_NETLINK
+       help
+         If this option is enabled, the kernel will include support
+         for user-space connection tracking helpers via NFNETLINK.
+
 config NETFILTER_NETLINK_QUEUE
        tristate "Netfilter NFQUEUE over NFNETLINK interface"
        depends on NETFILTER_ADVANCED
index 4e7960cc7b978fa37a1c8f2577b0628da5f49170..2f3bc0f647ba48f4cd66430876c3d51182362865 100644 (file)
@@ -9,6 +9,7 @@ obj-$(CONFIG_NETFILTER) = netfilter.o
 
 obj-$(CONFIG_NETFILTER_NETLINK) += nfnetlink.o
 obj-$(CONFIG_NETFILTER_NETLINK_ACCT) += nfnetlink_acct.o
+obj-$(CONFIG_NETFILTER_NETLINK_CTHELPER) += nfnetlink_cthelper.o
 obj-$(CONFIG_NETFILTER_NETLINK_QUEUE) += nfnetlink_queue.o
 obj-$(CONFIG_NETFILTER_NETLINK_LOG) += nfnetlink_log.o
 
index 9c18ecb0ab81e664d0b64e414d4b9bb2102832fe..2918ec2e450974ffba9fb5354a3f3640871187a2 100644 (file)
 #include <net/netfilter/nf_conntrack_extend.h>
 
 static DEFINE_MUTEX(nf_ct_helper_mutex);
-static struct hlist_head *nf_ct_helper_hash __read_mostly;
-static unsigned int nf_ct_helper_hsize __read_mostly;
+struct hlist_head *nf_ct_helper_hash __read_mostly;
+EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
+unsigned int nf_ct_helper_hsize __read_mostly;
+EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
 static unsigned int nf_ct_helper_count __read_mostly;
 
 static bool nf_ct_auto_assign_helper __read_mostly = true;
@@ -322,6 +324,9 @@ EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 
 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 {
+       int ret = 0;
+       struct nf_conntrack_helper *cur;
+       struct hlist_node *n;
        unsigned int h = helper_hash(&me->tuple);
 
        BUG_ON(me->expect_policy == NULL);
@@ -329,11 +334,19 @@ int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
        BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 
        mutex_lock(&nf_ct_helper_mutex);
+       hlist_for_each_entry(cur, n, &nf_ct_helper_hash[h], hnode) {
+               if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
+                   cur->tuple.src.l3num == me->tuple.src.l3num &&
+                   cur->tuple.dst.protonum == me->tuple.dst.protonum) {
+                       ret = -EEXIST;
+                       goto out;
+               }
+       }
        hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
        nf_ct_helper_count++;
+out:
        mutex_unlock(&nf_ct_helper_mutex);
-
-       return 0;
+       return ret;
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 
diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
new file mode 100644 (file)
index 0000000..d683619
--- /dev/null
@@ -0,0 +1,672 @@
+/*
+ * (C) 2012 Pablo Neira Ayuso <pablo@netfilter.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation (or any later at your option).
+ *
+ * This software has been sponsored by Vyatta Inc. <http://www.vyatta.com>
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/netlink.h>
+#include <linux/rculist.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/list.h>
+#include <linux/errno.h>
+#include <net/netlink.h>
+#include <net/sock.h>
+
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+#include <net/netfilter/nf_conntrack_ecache.h>
+
+#include <linux/netfilter/nfnetlink.h>
+#include <linux/netfilter/nfnetlink_conntrack.h>
+#include <linux/netfilter/nfnetlink_cthelper.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
+MODULE_DESCRIPTION("nfnl_cthelper: User-space connection tracking helpers");
+
+static int
+nfnl_userspace_cthelper(struct sk_buff *skb, unsigned int protoff,
+                       struct nf_conn *ct, enum ip_conntrack_info ctinfo)
+{
+       const struct nf_conn_help *help;
+       struct nf_conntrack_helper *helper;
+
+       help = nfct_help(ct);
+       if (help == NULL)
+               return NF_DROP;
+
+       /* rcu_read_lock()ed by nf_hook_slow */
+       helper = rcu_dereference(help->helper);
+       if (helper == NULL)
+               return NF_DROP;
+
+       /* This is an user-space helper not yet configured, skip. */
+       if ((helper->flags &
+           (NF_CT_HELPER_F_USERSPACE | NF_CT_HELPER_F_CONFIGURED)) ==
+            NF_CT_HELPER_F_USERSPACE)
+               return NF_ACCEPT;
+
+       /* If the user-space helper is not available, don't block traffic. */
+       return NF_QUEUE_NR(helper->queue_num) | NF_VERDICT_FLAG_QUEUE_BYPASS;
+}
+
+static const struct nla_policy nfnl_cthelper_tuple_pol[NFCTH_TUPLE_MAX+1] = {
+       [NFCTH_TUPLE_L3PROTONUM] = { .type = NLA_U16, },
+       [NFCTH_TUPLE_L4PROTONUM] = { .type = NLA_U8, },
+};
+
+static int
+nfnl_cthelper_parse_tuple(struct nf_conntrack_tuple *tuple,
+                         const struct nlattr *attr)
+{
+       struct nlattr *tb[NFCTH_TUPLE_MAX+1];
+
+       nla_parse_nested(tb, NFCTH_TUPLE_MAX, attr, nfnl_cthelper_tuple_pol);
+
+       if (!tb[NFCTH_TUPLE_L3PROTONUM] || !tb[NFCTH_TUPLE_L4PROTONUM])
+               return -EINVAL;
+
+       tuple->src.l3num = ntohs(nla_get_u16(tb[NFCTH_TUPLE_L3PROTONUM]));
+       tuple->dst.protonum = nla_get_u8(tb[NFCTH_TUPLE_L4PROTONUM]);
+
+       return 0;
+}
+
+static int
+nfnl_cthelper_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
+{
+       const struct nf_conn_help *help = nfct_help(ct);
+
+       if (help->helper->data_len == 0)
+               return -EINVAL;
+
+       memcpy(&help->data, nla_data(attr), help->helper->data_len);
+       return 0;
+}
+
+static int
+nfnl_cthelper_to_nlattr(struct sk_buff *skb, const struct nf_conn *ct)
+{
+       const struct nf_conn_help *help = nfct_help(ct);
+
+       if (help->helper->data_len &&
+           nla_put(skb, CTA_HELP_INFO, help->helper->data_len, &help->data))
+               goto nla_put_failure;
+
+       return 0;
+
+nla_put_failure:
+       return -ENOSPC;
+}
+
+static const struct nla_policy nfnl_cthelper_expect_pol[NFCTH_POLICY_MAX+1] = {
+       [NFCTH_POLICY_NAME] = { .type = NLA_NUL_STRING,
+                               .len = NF_CT_HELPER_NAME_LEN-1 },
+       [NFCTH_POLICY_EXPECT_MAX] = { .type = NLA_U32, },
+       [NFCTH_POLICY_EXPECT_TIMEOUT] = { .type = NLA_U32, },
+};
+
+static int
+nfnl_cthelper_expect_policy(struct nf_conntrack_expect_policy *expect_policy,
+                           const struct nlattr *attr)
+{
+       struct nlattr *tb[NFCTH_POLICY_MAX+1];
+
+       nla_parse_nested(tb, NFCTH_POLICY_MAX, attr, nfnl_cthelper_expect_pol);
+
+       if (!tb[NFCTH_POLICY_NAME] ||
+           !tb[NFCTH_POLICY_EXPECT_MAX] ||
+           !tb[NFCTH_POLICY_EXPECT_TIMEOUT])
+               return -EINVAL;
+
+       strncpy(expect_policy->name,
+               nla_data(tb[NFCTH_POLICY_NAME]), NF_CT_HELPER_NAME_LEN);
+       expect_policy->max_expected =
+               ntohl(nla_get_be32(tb[NFCTH_POLICY_EXPECT_MAX]));
+       expect_policy->timeout =
+               ntohl(nla_get_be32(tb[NFCTH_POLICY_EXPECT_TIMEOUT]));
+
+       return 0;
+}
+
+static const struct nla_policy
+nfnl_cthelper_expect_policy_set[NFCTH_POLICY_SET_MAX+1] = {
+       [NFCTH_POLICY_SET_NUM] = { .type = NLA_U32, },
+};
+
+static int
+nfnl_cthelper_parse_expect_policy(struct nf_conntrack_helper *helper,
+                                 const struct nlattr *attr)
+{
+       int i, ret;
+       struct nf_conntrack_expect_policy *expect_policy;
+       struct nlattr *tb[NFCTH_POLICY_SET_MAX+1];
+
+       nla_parse_nested(tb, NFCTH_POLICY_SET_MAX, attr,
+                                       nfnl_cthelper_expect_policy_set);
+
+       if (!tb[NFCTH_POLICY_SET_NUM])
+               return -EINVAL;
+
+       helper->expect_class_max =
+               ntohl(nla_get_be32(tb[NFCTH_POLICY_SET_NUM]));
+
+       if (helper->expect_class_max != 0 &&
+           helper->expect_class_max > NF_CT_MAX_EXPECT_CLASSES)
+               return -EOVERFLOW;
+
+       expect_policy = kzalloc(sizeof(struct nf_conntrack_expect_policy) *
+                               helper->expect_class_max, GFP_KERNEL);
+       if (expect_policy == NULL)
+               return -ENOMEM;
+
+       for (i=0; i<helper->expect_class_max; i++) {
+               if (!tb[NFCTH_POLICY_SET+i])
+                       goto err;
+
+               ret = nfnl_cthelper_expect_policy(&expect_policy[i],
+                                                 tb[NFCTH_POLICY_SET+i]);
+               if (ret < 0)
+                       goto err;
+       }
+       helper->expect_policy = expect_policy;
+       return 0;
+err:
+       kfree(expect_policy);
+       return -EINVAL;
+}
+
+static int
+nfnl_cthelper_create(const struct nlattr * const tb[],
+                    struct nf_conntrack_tuple *tuple)
+{
+       struct nf_conntrack_helper *helper;
+       int ret;
+
+       if (!tb[NFCTH_TUPLE] || !tb[NFCTH_POLICY] || !tb[NFCTH_PRIV_DATA_LEN])
+               return -EINVAL;
+
+       helper = kzalloc(sizeof(struct nf_conntrack_helper), GFP_KERNEL);
+       if (helper == NULL)
+               return -ENOMEM;
+
+       ret = nfnl_cthelper_parse_expect_policy(helper, tb[NFCTH_POLICY]);
+       if (ret < 0)
+               goto err;
+
+       strncpy(helper->name, nla_data(tb[NFCTH_NAME]), NF_CT_HELPER_NAME_LEN);
+       helper->data_len = ntohl(nla_get_be32(tb[NFCTH_PRIV_DATA_LEN]));
+       helper->flags |= NF_CT_HELPER_F_USERSPACE;
+       memcpy(&helper->tuple, tuple, sizeof(struct nf_conntrack_tuple));
+
+       helper->me = THIS_MODULE;
+       helper->help = nfnl_userspace_cthelper;
+       helper->from_nlattr = nfnl_cthelper_from_nlattr;
+       helper->to_nlattr = nfnl_cthelper_to_nlattr;
+
+       /* Default to queue number zero, this can be updated at any time. */
+       if (tb[NFCTH_QUEUE_NUM])
+               helper->queue_num = ntohl(nla_get_be32(tb[NFCTH_QUEUE_NUM]));
+
+       if (tb[NFCTH_STATUS]) {
+               int status = ntohl(nla_get_be32(tb[NFCTH_STATUS]));
+
+               switch(status) {
+               case NFCT_HELPER_STATUS_ENABLED:
+                       helper->flags |= NF_CT_HELPER_F_CONFIGURED;
+                       break;
+               case NFCT_HELPER_STATUS_DISABLED:
+                       helper->flags &= ~NF_CT_HELPER_F_CONFIGURED;
+                       break;
+               }
+       }
+
+       ret = nf_conntrack_helper_register(helper);
+       if (ret < 0)
+               goto err;
+
+       return 0;
+err:
+       kfree(helper);
+       return ret;
+}
+
+static int
+nfnl_cthelper_update(const struct nlattr * const tb[],
+                    struct nf_conntrack_helper *helper)
+{
+       int ret;
+
+       if (tb[NFCTH_PRIV_DATA_LEN])
+               return -EBUSY;
+
+       if (tb[NFCTH_POLICY]) {
+               ret = nfnl_cthelper_parse_expect_policy(helper,
+                                                       tb[NFCTH_POLICY]);
+               if (ret < 0)
+                       return ret;
+       }
+       if (tb[NFCTH_QUEUE_NUM])
+               helper->queue_num = ntohl(nla_get_be32(tb[NFCTH_QUEUE_NUM]));
+
+       if (tb[NFCTH_STATUS]) {
+               int status = ntohl(nla_get_be32(tb[NFCTH_STATUS]));
+
+               switch(status) {
+               case NFCT_HELPER_STATUS_ENABLED:
+                       helper->flags |= NF_CT_HELPER_F_CONFIGURED;
+                       break;
+               case NFCT_HELPER_STATUS_DISABLED:
+                       helper->flags &= ~NF_CT_HELPER_F_CONFIGURED;
+                       break;
+               }
+       }
+       return 0;
+}
+
+static int
+nfnl_cthelper_new(struct sock *nfnl, struct sk_buff *skb,
+                 const struct nlmsghdr *nlh, const struct nlattr * const tb[])
+{
+       const char *helper_name;
+       struct nf_conntrack_helper *cur, *helper = NULL;
+       struct nf_conntrack_tuple tuple;
+       struct hlist_node *n;
+       int ret = 0, i;
+
+       if (!tb[NFCTH_NAME] || !tb[NFCTH_TUPLE])
+               return -EINVAL;
+
+       helper_name = nla_data(tb[NFCTH_NAME]);
+
+       ret = nfnl_cthelper_parse_tuple(&tuple, tb[NFCTH_TUPLE]);
+       if (ret < 0)
+               return ret;
+
+       rcu_read_lock();
+       for (i = 0; i < nf_ct_helper_hsize && !helper; i++) {
+               hlist_for_each_entry_rcu(cur, n, &nf_ct_helper_hash[i], hnode) {
+
+                       /* skip non-userspace conntrack helpers. */
+                       if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
+                               continue;
+
+                       if (strncmp(cur->name, helper_name,
+                                       NF_CT_HELPER_NAME_LEN) != 0)
+                               continue;
+
+                       if ((tuple.src.l3num != cur->tuple.src.l3num ||
+                            tuple.dst.protonum != cur->tuple.dst.protonum))
+                               continue;
+
+                       if (nlh->nlmsg_flags & NLM_F_EXCL) {
+                               ret = -EEXIST;
+                               goto err;
+                       }
+                       helper = cur;
+                       break;
+               }
+       }
+       rcu_read_unlock();
+
+       if (helper == NULL)
+               ret = nfnl_cthelper_create(tb, &tuple);
+       else
+               ret = nfnl_cthelper_update(tb, helper);
+
+       return ret;
+err:
+       rcu_read_unlock();
+       return ret;
+}
+
+static int
+nfnl_cthelper_dump_tuple(struct sk_buff *skb,
+                        struct nf_conntrack_helper *helper)
+{
+       struct nlattr *nest_parms;
+
+       nest_parms = nla_nest_start(skb, NFCTH_TUPLE | NLA_F_NESTED);
+       if (nest_parms == NULL)
+               goto nla_put_failure;
+
+       if (nla_put_be16(skb, NFCTH_TUPLE_L3PROTONUM,
+                        htons(helper->tuple.src.l3num)))
+               goto nla_put_failure;
+
+       if (nla_put_u8(skb, NFCTH_TUPLE_L4PROTONUM, helper->tuple.dst.protonum))
+               goto nla_put_failure;
+
+       nla_nest_end(skb, nest_parms);
+       return 0;
+
+nla_put_failure:
+       return -1;
+}
+
+static int
+nfnl_cthelper_dump_policy(struct sk_buff *skb,
+                       struct nf_conntrack_helper *helper)
+{
+       int i;
+       struct nlattr *nest_parms1, *nest_parms2;
+
+       nest_parms1 = nla_nest_start(skb, NFCTH_POLICY | NLA_F_NESTED);
+       if (nest_parms1 == NULL)
+               goto nla_put_failure;
+
+       if (nla_put_be32(skb, NFCTH_POLICY_SET_NUM,
+                        htonl(helper->expect_class_max)))
+               goto nla_put_failure;
+
+       for (i=0; i<helper->expect_class_max; i++) {
+               nest_parms2 = nla_nest_start(skb,
+                               (NFCTH_POLICY_SET+i) | NLA_F_NESTED);
+               if (nest_parms2 == NULL)
+                       goto nla_put_failure;
+
+               if (nla_put_string(skb, NFCTH_POLICY_NAME,
+                                  helper->expect_policy[i].name))
+                       goto nla_put_failure;
+
+               if (nla_put_be32(skb, NFCTH_POLICY_EXPECT_MAX,
+                                htonl(helper->expect_policy[i].max_expected)))
+                       goto nla_put_failure;
+
+               if (nla_put_be32(skb, NFCTH_POLICY_EXPECT_TIMEOUT,
+                                htonl(helper->expect_policy[i].timeout)))
+                       goto nla_put_failure;
+
+               nla_nest_end(skb, nest_parms2);
+       }
+       nla_nest_end(skb, nest_parms1);
+       return 0;
+
+nla_put_failure:
+       return -1;
+}
+
+static int
+nfnl_cthelper_fill_info(struct sk_buff *skb, u32 pid, u32 seq, u32 type,
+                       int event, struct nf_conntrack_helper *helper)
+{
+       struct nlmsghdr *nlh;
+       struct nfgenmsg *nfmsg;
+       unsigned int flags = pid ? NLM_F_MULTI : 0;
+       int status;
+
+       event |= NFNL_SUBSYS_CTHELPER << 8;
+       nlh = nlmsg_put(skb, pid, seq, event, sizeof(*nfmsg), flags);
+       if (nlh == NULL)
+               goto nlmsg_failure;
+
+       nfmsg = nlmsg_data(nlh);
+       nfmsg->nfgen_family = AF_UNSPEC;
+       nfmsg->version = NFNETLINK_V0;
+       nfmsg->res_id = 0;
+
+       if (nla_put_string(skb, NFCTH_NAME, helper->name))
+               goto nla_put_failure;
+
+       if (nla_put_be32(skb, NFCTH_QUEUE_NUM, htonl(helper->queue_num)))
+               goto nla_put_failure;
+
+       if (nfnl_cthelper_dump_tuple(skb, helper) < 0)
+               goto nla_put_failure;
+
+       if (nfnl_cthelper_dump_policy(skb, helper) < 0)
+               goto nla_put_failure;
+
+       if (nla_put_be32(skb, NFCTH_PRIV_DATA_LEN, htonl(helper->data_len)))
+               goto nla_put_failure;
+
+       if (helper->flags & NF_CT_HELPER_F_CONFIGURED)
+               status = NFCT_HELPER_STATUS_ENABLED;
+       else
+               status = NFCT_HELPER_STATUS_DISABLED;
+
+       if (nla_put_be32(skb, NFCTH_STATUS, htonl(status)))
+               goto nla_put_failure;
+
+       nlmsg_end(skb, nlh);
+       return skb->len;
+
+nlmsg_failure:
+nla_put_failure:
+       nlmsg_cancel(skb, nlh);
+       return -1;
+}
+
+static int
+nfnl_cthelper_dump_table(struct sk_buff *skb, struct netlink_callback *cb)
+{
+       struct nf_conntrack_helper *cur, *last;
+       struct hlist_node *n;
+
+       rcu_read_lock();
+       last = (struct nf_conntrack_helper *)cb->args[1];
+       for (; cb->args[0] < nf_ct_helper_hsize; cb->args[0]++) {
+restart:
+               hlist_for_each_entry_rcu(cur, n,
+                               &nf_ct_helper_hash[cb->args[0]], hnode) {
+
+                       /* skip non-userspace conntrack helpers. */
+                       if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
+                               continue;
+
+                       if (cb->args[1]) {
+                               if (cur != last)
+                                       continue;
+                               cb->args[1] = 0;
+                       }
+                       if (nfnl_cthelper_fill_info(skb,
+                                           NETLINK_CB(cb->skb).pid,
+                                           cb->nlh->nlmsg_seq,
+                                           NFNL_MSG_TYPE(cb->nlh->nlmsg_type),
+                                           NFNL_MSG_CTHELPER_NEW, cur) < 0) {
+                               cb->args[1] = (unsigned long)cur;
+                               goto out;
+                       }
+               }
+       }
+       if (cb->args[1]) {
+               cb->args[1] = 0;
+               goto restart;
+       }
+out:
+       rcu_read_unlock();
+       return skb->len;
+}
+
+static int
+nfnl_cthelper_get(struct sock *nfnl, struct sk_buff *skb,
+                 const struct nlmsghdr *nlh, const struct nlattr * const tb[])
+{
+       int ret = -ENOENT, i;
+       struct nf_conntrack_helper *cur;
+       struct hlist_node *n;
+       struct sk_buff *skb2;
+       char *helper_name = NULL;
+       struct nf_conntrack_tuple tuple;
+       bool tuple_set = false;
+
+       if (nlh->nlmsg_flags & NLM_F_DUMP) {
+               struct netlink_dump_control c = {
+                       .dump = nfnl_cthelper_dump_table,
+               };
+               return netlink_dump_start(nfnl, skb, nlh, &c);
+       }
+
+       if (tb[NFCTH_NAME])
+               helper_name = nla_data(tb[NFCTH_NAME]);
+
+       if (tb[NFCTH_TUPLE]) {
+               ret = nfnl_cthelper_parse_tuple(&tuple, tb[NFCTH_TUPLE]);
+               if (ret < 0)
+                       return ret;
+
+               tuple_set = true;
+       }
+
+       for (i = 0; i < nf_ct_helper_hsize; i++) {
+               hlist_for_each_entry_rcu(cur, n, &nf_ct_helper_hash[i], hnode) {
+
+                       /* skip non-userspace conntrack helpers. */
+                       if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
+                               continue;
+
+                       if (helper_name && strncmp(cur->name, helper_name,
+                                               NF_CT_HELPER_NAME_LEN) != 0) {
+                               continue;
+                       }
+                       if (tuple_set &&
+                           (tuple.src.l3num != cur->tuple.src.l3num ||
+                            tuple.dst.protonum != cur->tuple.dst.protonum))
+                               continue;
+
+                       skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+                       if (skb2 == NULL) {
+                               ret = -ENOMEM;
+                               break;
+                       }
+
+                       ret = nfnl_cthelper_fill_info(skb2, NETLINK_CB(skb).pid,
+                                               nlh->nlmsg_seq,
+                                               NFNL_MSG_TYPE(nlh->nlmsg_type),
+                                               NFNL_MSG_CTHELPER_NEW, cur);
+                       if (ret <= 0) {
+                               kfree_skb(skb2);
+                               break;
+                       }
+
+                       ret = netlink_unicast(nfnl, skb2, NETLINK_CB(skb).pid,
+                                               MSG_DONTWAIT);
+                       if (ret > 0)
+                               ret = 0;
+
+                       /* this avoids a loop in nfnetlink. */
+                       return ret == -EAGAIN ? -ENOBUFS : ret;
+               }
+       }
+       return ret;
+}
+
+static int
+nfnl_cthelper_del(struct sock *nfnl, struct sk_buff *skb,
+            const struct nlmsghdr *nlh, const struct nlattr * const tb[])
+{
+       char *helper_name = NULL;
+       struct nf_conntrack_helper *cur;
+       struct hlist_node *n, *tmp;
+       struct nf_conntrack_tuple tuple;
+       bool tuple_set = false, found = false;
+       int i, j = 0, ret;
+
+       if (tb[NFCTH_NAME])
+               helper_name = nla_data(tb[NFCTH_NAME]);
+
+       if (tb[NFCTH_TUPLE]) {
+               ret = nfnl_cthelper_parse_tuple(&tuple, tb[NFCTH_TUPLE]);
+               if (ret < 0)
+                       return ret;
+
+               tuple_set = true;
+       }
+
+       for (i = 0; i < nf_ct_helper_hsize; i++) {
+               hlist_for_each_entry_safe(cur, n, tmp, &nf_ct_helper_hash[i],
+                                                               hnode) {
+                       /* skip non-userspace conntrack helpers. */
+                       if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
+                               continue;
+
+                       j++;
+
+                       if (helper_name && strncmp(cur->name, helper_name,
+                                               NF_CT_HELPER_NAME_LEN) != 0) {
+                               continue;
+                       }
+                       if (tuple_set &&
+                           (tuple.src.l3num != cur->tuple.src.l3num ||
+                            tuple.dst.protonum != cur->tuple.dst.protonum))
+                               continue;
+
+                       found = true;
+                       nf_conntrack_helper_unregister(cur);
+               }
+       }
+       /* Make sure we return success if we flush and there is no helpers */
+       return (found || j == 0) ? 0 : -ENOENT;
+}
+
+static const struct nla_policy nfnl_cthelper_policy[NFCTH_MAX+1] = {
+       [NFCTH_NAME] = { .type = NLA_NUL_STRING,
+                        .len = NF_CT_HELPER_NAME_LEN-1 },
+       [NFCTH_QUEUE_NUM] = { .type = NLA_U32, },
+};
+
+static const struct nfnl_callback nfnl_cthelper_cb[NFNL_MSG_CTHELPER_MAX] = {
+       [NFNL_MSG_CTHELPER_NEW]         = { .call = nfnl_cthelper_new,
+                                           .attr_count = NFCTH_MAX,
+                                           .policy = nfnl_cthelper_policy },
+       [NFNL_MSG_CTHELPER_GET]         = { .call = nfnl_cthelper_get,
+                                           .attr_count = NFCTH_MAX,
+                                           .policy = nfnl_cthelper_policy },
+       [NFNL_MSG_CTHELPER_DEL]         = { .call = nfnl_cthelper_del,
+                                           .attr_count = NFCTH_MAX,
+                                           .policy = nfnl_cthelper_policy },
+};
+
+static const struct nfnetlink_subsystem nfnl_cthelper_subsys = {
+       .name                           = "cthelper",
+       .subsys_id                      = NFNL_SUBSYS_CTHELPER,
+       .cb_count                       = NFNL_MSG_CTHELPER_MAX,
+       .cb                             = nfnl_cthelper_cb,
+};
+
+MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_CTHELPER);
+
+static int __init nfnl_cthelper_init(void)
+{
+       int ret;
+
+       ret = nfnetlink_subsys_register(&nfnl_cthelper_subsys);
+       if (ret < 0) {
+               pr_err("nfnl_cthelper: cannot register with nfnetlink.\n");
+               goto err_out;
+       }
+       return 0;
+err_out:
+       return ret;
+}
+
+static void __exit nfnl_cthelper_exit(void)
+{
+       struct nf_conntrack_helper *cur;
+       struct hlist_node *n, *tmp;
+       int i;
+
+       nfnetlink_subsys_unregister(&nfnl_cthelper_subsys);
+
+       for (i=0; i<nf_ct_helper_hsize; i++) {
+               hlist_for_each_entry_safe(cur, n, tmp, &nf_ct_helper_hash[i],
+                                                                       hnode) {
+                       /* skip non-userspace conntrack helpers. */
+                       if (!(cur->flags & NF_CT_HELPER_F_USERSPACE))
+                               continue;
+
+                       nf_conntrack_helper_unregister(cur);
+               }
+       }
+}
+
+module_init(nfnl_cthelper_init);
+module_exit(nfnl_cthelper_exit);