/*
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* Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
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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/module.h>
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#include <linux/skbuff.h>
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#include <net/ip6_checksum.h>
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#include <net/ip6_route.h>
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#include <net/tcp.h>
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#include <linux/netfilter_ipv6/ip6_tables.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter/xt_SYNPROXY.h>
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#include <net/netfilter/nf_conntrack.h>
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#include <net/netfilter/nf_conntrack_seqadj.h>
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#include <net/netfilter/nf_conntrack_synproxy.h>
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#include <net/netfilter/nf_conntrack_ecache.h>
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static struct ipv6hdr *
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synproxy_build_ip(struct net *net, struct sk_buff *skb,
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const struct in6_addr *saddr,
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const struct in6_addr *daddr)
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{
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struct ipv6hdr *iph;
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skb_reset_network_header(skb);
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iph = skb_put(skb, sizeof(*iph));
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ip6_flow_hdr(iph, 0, 0);
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iph->hop_limit = net->ipv6.devconf_all->hop_limit;
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iph->nexthdr = IPPROTO_TCP;
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iph->saddr = *saddr;
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iph->daddr = *daddr;
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return iph;
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}
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static void
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synproxy_send_tcp(struct net *net,
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const struct sk_buff *skb, struct sk_buff *nskb,
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struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
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struct ipv6hdr *niph, struct tcphdr *nth,
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unsigned int tcp_hdr_size)
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{
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struct dst_entry *dst;
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struct flowi6 fl6;
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nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
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nskb->ip_summed = CHECKSUM_PARTIAL;
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nskb->csum_start = (unsigned char *)nth - nskb->head;
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nskb->csum_offset = offsetof(struct tcphdr, check);
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memset(&fl6, 0, sizeof(fl6));
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fl6.flowi6_proto = IPPROTO_TCP;
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fl6.saddr = niph->saddr;
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fl6.daddr = niph->daddr;
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fl6.fl6_sport = nth->source;
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fl6.fl6_dport = nth->dest;
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security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
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dst = ip6_route_output(net, NULL, &fl6);
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if (dst->error) {
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dst_release(dst);
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goto free_nskb;
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}
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dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
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if (IS_ERR(dst))
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goto free_nskb;
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skb_dst_set(nskb, dst);
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if (nfct) {
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nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
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nf_conntrack_get(nfct);
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}
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ip6_local_out(net, nskb->sk, nskb);
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return;
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free_nskb:
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kfree_skb(nskb);
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}
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static void
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synproxy_send_client_synack(struct net *net,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts)
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{
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struct sk_buff *nskb;
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struct ipv6hdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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u16 mss = opts->mss;
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iph = ipv6_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
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skb_reset_transport_header(nskb);
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nth = skb_put(nskb, tcp_hdr_size);
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nth->source = th->dest;
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nth->dest = th->source;
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nth->seq = htonl(__cookie_v6_init_sequence(iph, th, &mss));
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nth->ack_seq = htonl(ntohl(th->seq) + 1);
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tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
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if (opts->options & XT_SYNPROXY_OPT_ECN)
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tcp_flag_word(nth) |= TCP_FLAG_ECE;
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nth->doff = tcp_hdr_size / 4;
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nth->window = 0;
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
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IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
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}
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static void
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synproxy_send_server_syn(struct net *net,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts, u32 recv_seq)
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{
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struct synproxy_net *snet = synproxy_pernet(net);
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struct sk_buff *nskb;
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struct ipv6hdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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iph = ipv6_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
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skb_reset_transport_header(nskb);
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nth = skb_put(nskb, tcp_hdr_size);
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nth->source = th->source;
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nth->dest = th->dest;
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nth->seq = htonl(recv_seq - 1);
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/* ack_seq is used to relay our ISN to the synproxy hook to initialize
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* sequence number translation once a connection tracking entry exists.
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*/
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nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
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tcp_flag_word(nth) = TCP_FLAG_SYN;
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if (opts->options & XT_SYNPROXY_OPT_ECN)
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tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
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nth->doff = tcp_hdr_size / 4;
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nth->window = th->window;
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
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niph, nth, tcp_hdr_size);
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}
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static void
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synproxy_send_server_ack(struct net *net,
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const struct ip_ct_tcp *state,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts)
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{
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struct sk_buff *nskb;
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struct ipv6hdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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iph = ipv6_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
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skb_reset_transport_header(nskb);
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nth = skb_put(nskb, tcp_hdr_size);
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nth->source = th->dest;
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nth->dest = th->source;
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nth->seq = htonl(ntohl(th->ack_seq));
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nth->ack_seq = htonl(ntohl(th->seq) + 1);
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tcp_flag_word(nth) = TCP_FLAG_ACK;
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nth->doff = tcp_hdr_size / 4;
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nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
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}
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static void
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synproxy_send_client_ack(struct net *net,
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const struct sk_buff *skb, const struct tcphdr *th,
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const struct synproxy_options *opts)
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{
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struct sk_buff *nskb;
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struct ipv6hdr *iph, *niph;
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struct tcphdr *nth;
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unsigned int tcp_hdr_size;
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iph = ipv6_hdr(skb);
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tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
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nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
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GFP_ATOMIC);
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if (nskb == NULL)
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return;
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skb_reserve(nskb, MAX_TCP_HEADER);
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niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
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skb_reset_transport_header(nskb);
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nth = skb_put(nskb, tcp_hdr_size);
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nth->source = th->source;
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nth->dest = th->dest;
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nth->seq = htonl(ntohl(th->seq) + 1);
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nth->ack_seq = th->ack_seq;
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tcp_flag_word(nth) = TCP_FLAG_ACK;
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nth->doff = tcp_hdr_size / 4;
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nth->window = htons(ntohs(th->window) >> opts->wscale);
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nth->check = 0;
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nth->urg_ptr = 0;
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synproxy_build_options(nth, opts);
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synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
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IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
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}
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static bool
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synproxy_recv_client_ack(struct net *net,
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const struct sk_buff *skb, const struct tcphdr *th,
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struct synproxy_options *opts, u32 recv_seq)
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{
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struct synproxy_net *snet = synproxy_pernet(net);
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int mss;
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mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
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if (mss == 0) {
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this_cpu_inc(snet->stats->cookie_invalid);
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return false;
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}
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this_cpu_inc(snet->stats->cookie_valid);
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opts->mss = mss;
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opts->options |= XT_SYNPROXY_OPT_MSS;
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if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy_check_timestamp_cookie(opts);
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synproxy_send_server_syn(net, skb, th, opts, recv_seq);
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return true;
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}
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static unsigned int
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synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
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{
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const struct xt_synproxy_info *info = par->targinfo;
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struct net *net = xt_net(par);
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struct synproxy_net *snet = synproxy_pernet(net);
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struct synproxy_options opts = {};
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struct tcphdr *th, _th;
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if (nf_ip6_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
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return NF_DROP;
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th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
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if (th == NULL)
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return NF_DROP;
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if (!synproxy_parse_options(skb, par->thoff, th, &opts))
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return NF_DROP;
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if (th->syn && !(th->ack || th->fin || th->rst)) {
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/* Initial SYN from client */
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this_cpu_inc(snet->stats->syn_received);
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if (th->ece && th->cwr)
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opts.options |= XT_SYNPROXY_OPT_ECN;
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opts.options &= info->options;
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if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy_init_timestamp_cookie(info, &opts);
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else
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opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
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XT_SYNPROXY_OPT_SACK_PERM |
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XT_SYNPROXY_OPT_ECN);
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synproxy_send_client_synack(net, skb, th, &opts);
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consume_skb(skb);
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return NF_STOLEN;
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} else if (th->ack && !(th->fin || th->rst || th->syn)) {
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/* ACK from client */
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if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
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consume_skb(skb);
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return NF_STOLEN;
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} else {
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return NF_DROP;
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}
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}
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return XT_CONTINUE;
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}
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static unsigned int ipv6_synproxy_hook(void *priv,
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struct sk_buff *skb,
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const struct nf_hook_state *nhs)
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{
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struct net *net = nhs->net;
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struct synproxy_net *snet = synproxy_pernet(net);
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enum ip_conntrack_info ctinfo;
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struct nf_conn *ct;
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struct nf_conn_synproxy *synproxy;
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struct synproxy_options opts = {};
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const struct ip_ct_tcp *state;
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struct tcphdr *th, _th;
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__be16 frag_off;
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u8 nexthdr;
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int thoff;
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ct = nf_ct_get(skb, &ctinfo);
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if (ct == NULL)
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return NF_ACCEPT;
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synproxy = nfct_synproxy(ct);
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if (synproxy == NULL)
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return NF_ACCEPT;
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if (nf_is_loopback_packet(skb))
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return NF_ACCEPT;
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nexthdr = ipv6_hdr(skb)->nexthdr;
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thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
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&frag_off);
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if (thoff < 0 || nexthdr != IPPROTO_TCP)
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return NF_ACCEPT;
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th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
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if (th == NULL)
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return NF_DROP;
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state = &ct->proto.tcp;
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switch (state->state) {
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case TCP_CONNTRACK_CLOSE:
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if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
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nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
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ntohl(th->seq) + 1);
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break;
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}
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if (!th->syn || th->ack ||
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CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
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break;
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/* Reopened connection - reset the sequence number and timestamp
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* adjustments, they will get initialized once the connection is
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* reestablished.
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*/
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nf_ct_seqadj_init(ct, ctinfo, 0);
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synproxy->tsoff = 0;
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this_cpu_inc(snet->stats->conn_reopened);
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/* fall through */
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case TCP_CONNTRACK_SYN_SENT:
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if (!synproxy_parse_options(skb, thoff, th, &opts))
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return NF_DROP;
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if (!th->syn && th->ack &&
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CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
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/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
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* therefore we need to add 1 to make the SYN sequence
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* number match the one of first SYN.
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*/
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if (synproxy_recv_client_ack(net, skb, th, &opts,
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ntohl(th->seq) + 1)) {
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this_cpu_inc(snet->stats->cookie_retrans);
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consume_skb(skb);
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return NF_STOLEN;
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} else {
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return NF_DROP;
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}
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}
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synproxy->isn = ntohl(th->ack_seq);
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if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
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synproxy->its = opts.tsecr;
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nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
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break;
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case TCP_CONNTRACK_SYN_RECV:
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if (!th->syn || !th->ack)
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break;
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if (!synproxy_parse_options(skb, thoff, th, &opts))
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return NF_DROP;
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if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) {
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synproxy->tsoff = opts.tsval - synproxy->its;
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nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
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}
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opts.options &= ~(XT_SYNPROXY_OPT_MSS |
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XT_SYNPROXY_OPT_WSCALE |
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XT_SYNPROXY_OPT_SACK_PERM);
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swap(opts.tsval, opts.tsecr);
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synproxy_send_server_ack(net, state, skb, th, &opts);
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nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
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nf_conntrack_event_cache(IPCT_SEQADJ, ct);
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swap(opts.tsval, opts.tsecr);
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synproxy_send_client_ack(net, skb, th, &opts);
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consume_skb(skb);
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return NF_STOLEN;
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default:
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break;
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}
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synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
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return NF_ACCEPT;
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}
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static const struct nf_hook_ops ipv6_synproxy_ops[] = {
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{
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.hook = ipv6_synproxy_hook,
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.pf = NFPROTO_IPV6,
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.hooknum = NF_INET_LOCAL_IN,
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.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
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},
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{
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.hook = ipv6_synproxy_hook,
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.pf = NFPROTO_IPV6,
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.hooknum = NF_INET_POST_ROUTING,
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.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
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},
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};
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static int synproxy_tg6_check(const struct xt_tgchk_param *par)
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{
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struct synproxy_net *snet = synproxy_pernet(par->net);
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const struct ip6t_entry *e = par->entryinfo;
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int err;
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if (!(e->ipv6.flags & IP6T_F_PROTO) ||
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e->ipv6.proto != IPPROTO_TCP ||
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e->ipv6.invflags & XT_INV_PROTO)
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return -EINVAL;
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err = nf_ct_netns_get(par->net, par->family);
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if (err)
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return err;
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if (snet->hook_ref6 == 0) {
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err = nf_register_net_hooks(par->net, ipv6_synproxy_ops,
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ARRAY_SIZE(ipv6_synproxy_ops));
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if (err) {
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nf_ct_netns_put(par->net, par->family);
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return err;
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}
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}
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snet->hook_ref6++;
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return err;
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}
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static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
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{
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struct synproxy_net *snet = synproxy_pernet(par->net);
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snet->hook_ref6--;
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if (snet->hook_ref6 == 0)
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nf_unregister_net_hooks(par->net, ipv6_synproxy_ops,
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ARRAY_SIZE(ipv6_synproxy_ops));
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nf_ct_netns_put(par->net, par->family);
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}
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static struct xt_target synproxy_tg6_reg __read_mostly = {
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.name = "SYNPROXY",
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.family = NFPROTO_IPV6,
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.hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
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.target = synproxy_tg6,
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.targetsize = sizeof(struct xt_synproxy_info),
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.checkentry = synproxy_tg6_check,
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.destroy = synproxy_tg6_destroy,
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.me = THIS_MODULE,
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};
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static int __init synproxy_tg6_init(void)
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{
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return xt_register_target(&synproxy_tg6_reg);
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}
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static void __exit synproxy_tg6_exit(void)
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{
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xt_unregister_target(&synproxy_tg6_reg);
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}
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module_init(synproxy_tg6_init);
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module_exit(synproxy_tg6_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
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