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* ip_conntrack_proto_gre.c - Version 3.0
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* Connection tracking protocol helper module for GRE.
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* GRE is a generic encapsulation protocol, which is generally not very
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* suited for NAT, as it has no protocol-specific part as port numbers.
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* It has an optional key field, which may help us distinguishing two
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* connections between the same two hosts.
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* GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
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* PPTP is built on top of a modified version of GRE, and has a mandatory
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* field called "CallID", which serves us for the same purpose as the key
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* Documentation about PPTP can be found in RFC 2637
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* (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
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* Development of this code funded by Astaro AG (http://www.astaro.com/)
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/timer.h>
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#include <linux/list.h>
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#include <linux/seq_file.h>
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#include <linux/netdevice.h>
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#include <linux/skbuff.h>
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#include <linux/slab.h>
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#include <net/net_namespace.h>
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#include <net/netns/generic.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 <linux/netfilter/nf_conntrack_proto_gre.h>
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#include <linux/netfilter/nf_conntrack_pptp.h>
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#define GRE_TIMEOUT (30 * HZ)
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#define GRE_STREAM_TIMEOUT (180 * HZ)
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static int proto_gre_net_id __read_mostly;
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struct netns_proto_gre {
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struct list_head keymap_list;
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void nf_ct_gre_keymap_flush(struct net *net)
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struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
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struct nf_ct_gre_keymap *km, *tmp;
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write_lock_bh(&net_gre->keymap_lock);
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list_for_each_entry_safe(km, tmp, &net_gre->keymap_list, list) {
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write_unlock_bh(&net_gre->keymap_lock);
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EXPORT_SYMBOL(nf_ct_gre_keymap_flush);
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static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
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const struct nf_conntrack_tuple *t)
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return km->tuple.src.l3num == t->src.l3num &&
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!memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
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!memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
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km->tuple.dst.protonum == t->dst.protonum &&
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km->tuple.dst.u.all == t->dst.u.all;
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/* look up the source key for a given tuple */
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static __be16 gre_keymap_lookup(struct net *net, struct nf_conntrack_tuple *t)
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struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
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struct nf_ct_gre_keymap *km;
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read_lock_bh(&net_gre->keymap_lock);
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list_for_each_entry(km, &net_gre->keymap_list, list) {
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if (gre_key_cmpfn(km, t)) {
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key = km->tuple.src.u.gre.key;
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read_unlock_bh(&net_gre->keymap_lock);
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pr_debug("lookup src key 0x%x for ", key);
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/* add a single keymap entry, associate with specified master ct */
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int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
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struct nf_conntrack_tuple *t)
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struct net *net = nf_ct_net(ct);
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struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
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struct nf_conn_help *help = nfct_help(ct);
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struct nf_ct_gre_keymap **kmp, *km;
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kmp = &help->help.ct_pptp_info.keymap[dir];
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/* check whether it's a retransmission */
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read_lock_bh(&net_gre->keymap_lock);
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list_for_each_entry(km, &net_gre->keymap_list, list) {
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if (gre_key_cmpfn(km, t) && km == *kmp) {
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read_unlock_bh(&net_gre->keymap_lock);
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read_unlock_bh(&net_gre->keymap_lock);
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pr_debug("trying to override keymap_%s for ct %p\n",
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dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
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km = kmalloc(sizeof(*km), GFP_ATOMIC);
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memcpy(&km->tuple, t, sizeof(*t));
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pr_debug("adding new entry %p: ", km);
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nf_ct_dump_tuple(&km->tuple);
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write_lock_bh(&net_gre->keymap_lock);
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list_add_tail(&km->list, &net_gre->keymap_list);
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write_unlock_bh(&net_gre->keymap_lock);
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EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
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/* destroy the keymap entries associated with specified master ct */
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void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
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struct net *net = nf_ct_net(ct);
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struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
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struct nf_conn_help *help = nfct_help(ct);
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enum ip_conntrack_dir dir;
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pr_debug("entering for ct %p\n", ct);
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write_lock_bh(&net_gre->keymap_lock);
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for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
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if (help->help.ct_pptp_info.keymap[dir]) {
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pr_debug("removing %p from list\n",
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help->help.ct_pptp_info.keymap[dir]);
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list_del(&help->help.ct_pptp_info.keymap[dir]->list);
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kfree(help->help.ct_pptp_info.keymap[dir]);
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help->help.ct_pptp_info.keymap[dir] = NULL;
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write_unlock_bh(&net_gre->keymap_lock);
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EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
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/* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
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/* invert gre part of tuple */
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static bool gre_invert_tuple(struct nf_conntrack_tuple *tuple,
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const struct nf_conntrack_tuple *orig)
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tuple->dst.u.gre.key = orig->src.u.gre.key;
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tuple->src.u.gre.key = orig->dst.u.gre.key;
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/* gre hdr info to tuple */
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static bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
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struct nf_conntrack_tuple *tuple)
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struct net *net = dev_net(skb->dev ? skb->dev : skb_dst(skb)->dev);
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const struct gre_hdr_pptp *pgrehdr;
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struct gre_hdr_pptp _pgrehdr;
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const struct gre_hdr *grehdr;
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struct gre_hdr _grehdr;
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/* first only delinearize old RFC1701 GRE header */
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grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
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if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
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/* try to behave like "nf_conntrack_proto_generic" */
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tuple->src.u.all = 0;
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tuple->dst.u.all = 0;
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/* PPTP header is variable length, only need up to the call_id field */
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pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
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if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
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pr_debug("GRE_VERSION_PPTP but unknown proto\n");
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tuple->dst.u.gre.key = pgrehdr->call_id;
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srckey = gre_keymap_lookup(net, tuple);
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tuple->src.u.gre.key = srckey;
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/* print gre part of tuple */
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static int gre_print_tuple(struct seq_file *s,
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const struct nf_conntrack_tuple *tuple)
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return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
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ntohs(tuple->src.u.gre.key),
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ntohs(tuple->dst.u.gre.key));
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/* print private data for conntrack */
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static int gre_print_conntrack(struct seq_file *s, struct nf_conn *ct)
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return seq_printf(s, "timeout=%u, stream_timeout=%u ",
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(ct->proto.gre.timeout / HZ),
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(ct->proto.gre.stream_timeout / HZ));
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/* Returns verdict for packet, and may modify conntrack */
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static int gre_packet(struct nf_conn *ct,
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const struct sk_buff *skb,
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unsigned int dataoff,
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enum ip_conntrack_info ctinfo,
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unsigned int hooknum)
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/* If we've seen traffic both ways, this is a GRE connection.
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if (ct->status & IPS_SEEN_REPLY) {
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nf_ct_refresh_acct(ct, ctinfo, skb,
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ct->proto.gre.stream_timeout);
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/* Also, more likely to be important, and not a probe. */
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if (!test_and_set_bit(IPS_ASSURED_BIT, &ct->status))
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nf_conntrack_event_cache(IPCT_ASSURED, ct);
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nf_ct_refresh_acct(ct, ctinfo, skb,
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ct->proto.gre.timeout);
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/* Called when a new connection for this protocol found. */
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static bool gre_new(struct nf_conn *ct, const struct sk_buff *skb,
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unsigned int dataoff)
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nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
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/* initialize to sane value. Ideally a conntrack helper
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* (e.g. in case of pptp) is increasing them */
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ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
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ct->proto.gre.timeout = GRE_TIMEOUT;
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/* Called when a conntrack entry has already been removed from the hashes
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* and is about to be deleted from memory */
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static void gre_destroy(struct nf_conn *ct)
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struct nf_conn *master = ct->master;
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pr_debug(" entering\n");
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pr_debug("no master !?!\n");
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nf_ct_gre_keymap_destroy(master);
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/* protocol helper struct */
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static struct nf_conntrack_l4proto nf_conntrack_l4proto_gre4 __read_mostly = {
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.l4proto = IPPROTO_GRE,
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.pkt_to_tuple = gre_pkt_to_tuple,
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.invert_tuple = gre_invert_tuple,
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.print_tuple = gre_print_tuple,
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.print_conntrack = gre_print_conntrack,
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.packet = gre_packet,
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.destroy = gre_destroy,
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#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
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.tuple_to_nlattr = nf_ct_port_tuple_to_nlattr,
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.nlattr_tuple_size = nf_ct_port_nlattr_tuple_size,
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.nlattr_to_tuple = nf_ct_port_nlattr_to_tuple,
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.nla_policy = nf_ct_port_nla_policy,
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static int proto_gre_net_init(struct net *net)
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struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
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rwlock_init(&net_gre->keymap_lock);
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INIT_LIST_HEAD(&net_gre->keymap_list);
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static void proto_gre_net_exit(struct net *net)
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nf_ct_gre_keymap_flush(net);
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static struct pernet_operations proto_gre_net_ops = {
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.init = proto_gre_net_init,
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.exit = proto_gre_net_exit,
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.id = &proto_gre_net_id,
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.size = sizeof(struct netns_proto_gre),
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static int __init nf_ct_proto_gre_init(void)
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rv = nf_conntrack_l4proto_register(&nf_conntrack_l4proto_gre4);
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rv = register_pernet_subsys(&proto_gre_net_ops);
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nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
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static void __exit nf_ct_proto_gre_fini(void)
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nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
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unregister_pernet_subsys(&proto_gre_net_ops);
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module_init(nf_ct_proto_gre_init);
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module_exit(nf_ct_proto_gre_fini);
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MODULE_LICENSE("GPL");