![Pablo Neira Ayuso](/assets/img/avatar_default.png)
Explicit helper attachment via the CT target is broken with NAT if non-standard ports are used. This problem was hidden behind the automatic helper assignment routine. Thus, it becomes more noticeable now that we can disable the automatic helper assignment with Eric Leblond's: 9e8ac5a netfilter: nf_ct_helper: allow to disable automatic helper assignment Basically, nf_conntrack_alter_reply asks for looking up the helper up if NAT is enabled. Unfortunately, we don't have the conntrack template at that point anymore. Since we don't want to rely on the automatic helper assignment, we can skip the second look-up and stick to the helper that was attached by iptables. With the CT target, the user is in full control of helper attachment, thus, the policy is to trust what the user explicitly configures via iptables (no automatic magic anymore). Interestingly, this bug was hidden by the automatic helper look-up code. But it can be easily trigger if you attach the helper in a non-standard port, eg. iptables -I PREROUTING -t raw -p tcp --dport 8888 \ -j CT --helper ftp And you disabled the automatic helper assignment. I added the IPS_HELPER_BIT that allows us to differenciate between a helper that has been explicitly attached and those that have been automatically assigned. I didn't come up with a better solution (having backward compatibility in mind). Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
441 lines
11 KiB
C
441 lines
11 KiB
C
/* Helper handling for netfilter. */
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/* (C) 1999-2001 Paul `Rusty' Russell
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* (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
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* (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/types.h>
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#include <linux/netfilter.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/vmalloc.h>
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#include <linux/stddef.h>
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#include <linux/random.h>
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#include <linux/err.h>
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#include <linux/kernel.h>
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#include <linux/netdevice.h>
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#include <linux/rculist.h>
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#include <linux/rtnetlink.h>
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#include <net/netfilter/nf_conntrack.h>
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#include <net/netfilter/nf_conntrack_l3proto.h>
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#include <net/netfilter/nf_conntrack_l4proto.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <net/netfilter/nf_conntrack_core.h>
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#include <net/netfilter/nf_conntrack_extend.h>
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static DEFINE_MUTEX(nf_ct_helper_mutex);
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static struct hlist_head *nf_ct_helper_hash __read_mostly;
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static unsigned int nf_ct_helper_hsize __read_mostly;
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static unsigned int nf_ct_helper_count __read_mostly;
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static bool nf_ct_auto_assign_helper __read_mostly = true;
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module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
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MODULE_PARM_DESC(nf_conntrack_helper,
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"Enable automatic conntrack helper assignment (default 1)");
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#ifdef CONFIG_SYSCTL
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static struct ctl_table helper_sysctl_table[] = {
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{
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.procname = "nf_conntrack_helper",
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.data = &init_net.ct.sysctl_auto_assign_helper,
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.maxlen = sizeof(unsigned int),
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.mode = 0644,
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.proc_handler = proc_dointvec,
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},
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{}
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};
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static int nf_conntrack_helper_init_sysctl(struct net *net)
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{
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struct ctl_table *table;
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table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
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GFP_KERNEL);
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if (!table)
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goto out;
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table[0].data = &net->ct.sysctl_auto_assign_helper;
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net->ct.helper_sysctl_header =
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register_net_sysctl(net, "net/netfilter", table);
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if (!net->ct.helper_sysctl_header) {
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pr_err("nf_conntrack_helper: can't register to sysctl.\n");
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goto out_register;
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}
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return 0;
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out_register:
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kfree(table);
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out:
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return -ENOMEM;
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}
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static void nf_conntrack_helper_fini_sysctl(struct net *net)
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{
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struct ctl_table *table;
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table = net->ct.helper_sysctl_header->ctl_table_arg;
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unregister_net_sysctl_table(net->ct.helper_sysctl_header);
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kfree(table);
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}
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#else
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static int nf_conntrack_helper_init_sysctl(struct net *net)
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{
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return 0;
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}
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static void nf_conntrack_helper_fini_sysctl(struct net *net)
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{
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}
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#endif /* CONFIG_SYSCTL */
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/* Stupid hash, but collision free for the default registrations of the
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* helpers currently in the kernel. */
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static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
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{
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return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
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(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
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}
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static struct nf_conntrack_helper *
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__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
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{
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struct nf_conntrack_helper *helper;
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struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
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struct hlist_node *n;
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unsigned int h;
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if (!nf_ct_helper_count)
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return NULL;
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h = helper_hash(tuple);
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hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
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if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
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return helper;
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}
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return NULL;
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}
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struct nf_conntrack_helper *
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__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
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{
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struct nf_conntrack_helper *h;
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struct hlist_node *n;
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unsigned int i;
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for (i = 0; i < nf_ct_helper_hsize; i++) {
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hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
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if (!strcmp(h->name, name) &&
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h->tuple.src.l3num == l3num &&
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h->tuple.dst.protonum == protonum)
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return h;
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}
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}
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return NULL;
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}
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EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
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struct nf_conntrack_helper *
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nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
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{
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struct nf_conntrack_helper *h;
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h = __nf_conntrack_helper_find(name, l3num, protonum);
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#ifdef CONFIG_MODULES
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if (h == NULL) {
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if (request_module("nfct-helper-%s", name) == 0)
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h = __nf_conntrack_helper_find(name, l3num, protonum);
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}
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#endif
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if (h != NULL && !try_module_get(h->me))
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h = NULL;
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return h;
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}
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EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
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struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
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{
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struct nf_conn_help *help;
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help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
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if (help)
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INIT_HLIST_HEAD(&help->expectations);
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else
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pr_debug("failed to add helper extension area");
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return help;
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}
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EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
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int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
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gfp_t flags)
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{
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struct nf_conntrack_helper *helper = NULL;
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struct nf_conn_help *help;
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struct net *net = nf_ct_net(ct);
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int ret = 0;
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/* We already got a helper explicitly attached. The function
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* nf_conntrack_alter_reply - in case NAT is in use - asks for looking
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* the helper up again. Since now the user is in full control of
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* making consistent helper configurations, skip this automatic
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* re-lookup, otherwise we'll lose the helper.
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*/
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if (test_bit(IPS_HELPER_BIT, &ct->status))
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return 0;
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if (tmpl != NULL) {
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help = nfct_help(tmpl);
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if (help != NULL) {
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helper = help->helper;
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set_bit(IPS_HELPER_BIT, &ct->status);
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}
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}
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help = nfct_help(ct);
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if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
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helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
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if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
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pr_info("nf_conntrack: automatic helper "
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"assignment is deprecated and it will "
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"be removed soon. Use the iptables CT target "
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"to attach helpers instead.\n");
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net->ct.auto_assign_helper_warned = true;
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}
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}
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if (helper == NULL) {
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if (help)
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RCU_INIT_POINTER(help->helper, NULL);
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goto out;
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}
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if (help == NULL) {
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help = nf_ct_helper_ext_add(ct, flags);
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if (help == NULL) {
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ret = -ENOMEM;
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goto out;
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}
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} else {
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memset(&help->help, 0, sizeof(help->help));
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}
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rcu_assign_pointer(help->helper, helper);
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out:
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return ret;
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}
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EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
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static inline int unhelp(struct nf_conntrack_tuple_hash *i,
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const struct nf_conntrack_helper *me)
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{
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struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
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struct nf_conn_help *help = nfct_help(ct);
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if (help && rcu_dereference_protected(
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help->helper,
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lockdep_is_held(&nf_conntrack_lock)
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) == me) {
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nf_conntrack_event(IPCT_HELPER, ct);
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RCU_INIT_POINTER(help->helper, NULL);
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}
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return 0;
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}
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void nf_ct_helper_destroy(struct nf_conn *ct)
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{
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struct nf_conn_help *help = nfct_help(ct);
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struct nf_conntrack_helper *helper;
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if (help) {
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rcu_read_lock();
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helper = rcu_dereference(help->helper);
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if (helper && helper->destroy)
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helper->destroy(ct);
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rcu_read_unlock();
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}
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}
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static LIST_HEAD(nf_ct_helper_expectfn_list);
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void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
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{
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spin_lock_bh(&nf_conntrack_lock);
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list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
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spin_unlock_bh(&nf_conntrack_lock);
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}
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EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
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void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
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{
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spin_lock_bh(&nf_conntrack_lock);
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list_del_rcu(&n->head);
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spin_unlock_bh(&nf_conntrack_lock);
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}
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EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
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struct nf_ct_helper_expectfn *
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nf_ct_helper_expectfn_find_by_name(const char *name)
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{
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struct nf_ct_helper_expectfn *cur;
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bool found = false;
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rcu_read_lock();
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list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
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if (!strcmp(cur->name, name)) {
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found = true;
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break;
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}
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}
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rcu_read_unlock();
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return found ? cur : NULL;
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}
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EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
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struct nf_ct_helper_expectfn *
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nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
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{
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struct nf_ct_helper_expectfn *cur;
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bool found = false;
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rcu_read_lock();
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list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
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if (cur->expectfn == symbol) {
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found = true;
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break;
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}
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}
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rcu_read_unlock();
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return found ? cur : NULL;
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}
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EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
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int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
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{
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unsigned int h = helper_hash(&me->tuple);
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BUG_ON(me->expect_policy == NULL);
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BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
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BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
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mutex_lock(&nf_ct_helper_mutex);
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hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
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nf_ct_helper_count++;
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mutex_unlock(&nf_ct_helper_mutex);
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return 0;
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}
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EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
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static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
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struct net *net)
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{
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struct nf_conntrack_tuple_hash *h;
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struct nf_conntrack_expect *exp;
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const struct hlist_node *n, *next;
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const struct hlist_nulls_node *nn;
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unsigned int i;
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/* Get rid of expectations */
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for (i = 0; i < nf_ct_expect_hsize; i++) {
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hlist_for_each_entry_safe(exp, n, next,
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&net->ct.expect_hash[i], hnode) {
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struct nf_conn_help *help = nfct_help(exp->master);
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if ((rcu_dereference_protected(
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help->helper,
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lockdep_is_held(&nf_conntrack_lock)
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) == me || exp->helper == me) &&
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del_timer(&exp->timeout)) {
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nf_ct_unlink_expect(exp);
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nf_ct_expect_put(exp);
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}
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}
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}
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/* Get rid of expecteds, set helpers to NULL. */
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hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
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unhelp(h, me);
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for (i = 0; i < net->ct.htable_size; i++) {
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hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
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unhelp(h, me);
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}
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}
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void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
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{
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struct net *net;
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mutex_lock(&nf_ct_helper_mutex);
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hlist_del_rcu(&me->hnode);
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nf_ct_helper_count--;
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mutex_unlock(&nf_ct_helper_mutex);
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/* Make sure every nothing is still using the helper unless its a
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* connection in the hash.
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*/
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synchronize_rcu();
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rtnl_lock();
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spin_lock_bh(&nf_conntrack_lock);
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for_each_net(net)
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__nf_conntrack_helper_unregister(me, net);
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spin_unlock_bh(&nf_conntrack_lock);
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rtnl_unlock();
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}
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EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
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static struct nf_ct_ext_type helper_extend __read_mostly = {
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.len = sizeof(struct nf_conn_help),
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.align = __alignof__(struct nf_conn_help),
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.id = NF_CT_EXT_HELPER,
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};
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int nf_conntrack_helper_init(struct net *net)
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{
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int err;
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net->ct.auto_assign_helper_warned = false;
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net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
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if (net_eq(net, &init_net)) {
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nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
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nf_ct_helper_hash =
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nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
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if (!nf_ct_helper_hash)
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return -ENOMEM;
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err = nf_ct_extend_register(&helper_extend);
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if (err < 0)
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goto err1;
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}
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err = nf_conntrack_helper_init_sysctl(net);
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if (err < 0)
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goto out_sysctl;
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return 0;
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out_sysctl:
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if (net_eq(net, &init_net))
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nf_ct_extend_unregister(&helper_extend);
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err1:
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nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
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return err;
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}
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void nf_conntrack_helper_fini(struct net *net)
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{
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nf_conntrack_helper_fini_sysctl(net);
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if (net_eq(net, &init_net)) {
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nf_ct_extend_unregister(&helper_extend);
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nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
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}
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}
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