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|
/*
* Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
*
* 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.
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/tcp.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_SYNPROXY.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_seqadj.h>
#include <net/netfilter/nf_conntrack_synproxy.h>
static struct iphdr *
synproxy_build_ip(struct sk_buff *skb, u32 saddr, u32 daddr)
{
struct iphdr *iph;
skb_reset_network_header(skb);
iph = (struct iphdr *)skb_put(skb, sizeof(*iph));
iph->version = 4;
iph->ihl = sizeof(*iph) / 4;
iph->tos = 0;
iph->id = 0;
iph->frag_off = htons(IP_DF);
iph->ttl = sysctl_ip_default_ttl;
iph->protocol = IPPROTO_TCP;
iph->check = 0;
iph->saddr = saddr;
iph->daddr = daddr;
return iph;
}
static void
synproxy_send_tcp(const struct sk_buff *skb, struct sk_buff *nskb,
struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
struct iphdr *niph, struct tcphdr *nth,
unsigned int tcp_hdr_size)
{
nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
nskb->ip_summed = CHECKSUM_PARTIAL;
nskb->csum_start = (unsigned char *)nth - nskb->head;
nskb->csum_offset = offsetof(struct tcphdr, check);
skb_dst_set_noref(nskb, skb_dst(skb));
nskb->protocol = htons(ETH_P_IP);
if (ip_route_me_harder(nskb, RTN_UNSPEC))
goto free_nskb;
if (nfct) {
nskb->nfct = nfct;
nskb->nfctinfo = ctinfo;
nf_conntrack_get(nfct);
}
ip_local_out(nskb);
return;
free_nskb:
kfree_skb(nskb);
}
static void
synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th,
const struct synproxy_options *opts)
{
struct sk_buff *nskb;
struct iphdr *iph, *niph;
struct tcphdr *nth;
unsigned int tcp_hdr_size;
u16 mss = opts->mss;
iph = ip_hdr(skb);
tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
GFP_ATOMIC);
if (nskb == NULL)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr);
skb_reset_transport_header(nskb);
nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
nth->source = th->dest;
nth->dest = th->source;
nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
nth->ack_seq = htonl(ntohl(th->seq) + 1);
tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
if (opts->options & XT_SYNPROXY_OPT_ECN)
tcp_flag_word(nth) |= TCP_FLAG_ECE;
nth->doff = tcp_hdr_size / 4;
nth->window = 0;
nth->check = 0;
nth->urg_ptr = 0;
synproxy_build_options(nth, opts);
synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
niph, nth, tcp_hdr_size);
}
static void
synproxy_send_server_syn(const struct synproxy_net *snet,
const struct sk_buff *skb, const struct tcphdr *th,
const struct synproxy_options *opts, u32 recv_seq)
{
struct sk_buff *nskb;
struct iphdr *iph, *niph;
struct tcphdr *nth;
unsigned int tcp_hdr_size;
iph = ip_hdr(skb);
tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
GFP_ATOMIC);
if (nskb == NULL)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr);
skb_reset_transport_header(nskb);
nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
nth->source = th->source;
nth->dest = th->dest;
nth->seq = htonl(recv_seq - 1);
/* ack_seq is used to relay our ISN to the synproxy hook to initialize
* sequence number translation once a connection tracking entry exists.
*/
nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
tcp_flag_word(nth) = TCP_FLAG_SYN;
if (opts->options & XT_SYNPROXY_OPT_ECN)
tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
nth->doff = tcp_hdr_size / 4;
nth->window = th->window;
nth->check = 0;
nth->urg_ptr = 0;
synproxy_build_options(nth, opts);
synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
niph, nth, tcp_hdr_size);
}
static void
synproxy_send_server_ack(const struct synproxy_net *snet,
const struct ip_ct_tcp *state,
const struct sk_buff *skb, const struct tcphdr *th,
const struct synproxy_options *opts)
{
struct sk_buff *nskb;
struct iphdr *iph, *niph;
struct tcphdr *nth;
unsigned int tcp_hdr_size;
iph = ip_hdr(skb);
tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
GFP_ATOMIC);
if (nskb == NULL)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr);
skb_reset_transport_header(nskb);
nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
nth->source = th->dest;
nth->dest = th->source;
nth->seq = htonl(ntohl(th->ack_seq));
nth->ack_seq = htonl(ntohl(th->seq) + 1);
tcp_flag_word(nth) = TCP_FLAG_ACK;
nth->doff = tcp_hdr_size / 4;
nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
nth->check = 0;
nth->urg_ptr = 0;
synproxy_build_options(nth, opts);
synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
}
static void
synproxy_send_client_ack(const struct synproxy_net
|