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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, __be32 saddr, __be32 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 synproxy_net *snet,
- 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)
- {
- struct net *net = nf_ct_net(snet->tmpl);
- 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(net, nskb, RTN_UNSPEC))
- goto free_nskb;
- if (nfct) {
- nskb->nfct = nfct;
- nskb->nfctinfo = ctinfo;
- nf_conntrack_get(nfct);
- }
- ip_local_out(net, nskb->sk, nskb);
- return;
- free_nskb:
- kfree_skb(nskb);
- }
- static void
- synproxy_send_client_synack(const struct synproxy_net *snet,
- 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(snet, 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(snet, 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(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
- }
- static void
- synproxy_send_client_ack(const struct synproxy_net *snet,
- 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->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(ntohl(th->seq) + 1);
- nth->ack_seq = th->ack_seq;
- tcp_flag_word(nth) = TCP_FLAG_ACK;
- nth->doff = tcp_hdr_size / 4;
- nth->window = htons(ntohs(th->window) >> opts->wscale);
- nth->check = 0;
- nth->urg_ptr = 0;
- synproxy_build_options(nth, opts);
- synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
- niph, nth, tcp_hdr_size);
- }
- static bool
- synproxy_recv_client_ack(const struct synproxy_net *snet,
- const struct sk_buff *skb, const struct tcphdr *th,
- struct synproxy_options *opts, u32 recv_seq)
- {
- int mss;
- mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
- if (mss == 0) {
- this_cpu_inc(snet->stats->cookie_invalid);
- return false;
- }
- this_cpu_inc(snet->stats->cookie_valid);
- opts->mss = mss;
- opts->options |= XT_SYNPROXY_OPT_MSS;
- if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
- synproxy_check_timestamp_cookie(opts);
- synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
- return true;
- }
- static unsigned int
- synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
- {
- const struct xt_synproxy_info *info = par->targinfo;
- struct synproxy_net *snet = synproxy_pernet(par->net);
- struct synproxy_options opts = {};
- struct tcphdr *th, _th;
- if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
- return NF_DROP;
- th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
- if (th == NULL)
- return NF_DROP;
- if (!synproxy_parse_options(skb, par->thoff, th, &opts))
- return NF_DROP;
- if (th->syn && !(th->ack || th->fin || th->rst)) {
- /* Initial SYN from client */
- this_cpu_inc(snet->stats->syn_received);
- if (th->ece && th->cwr)
- opts.options |= XT_SYNPROXY_OPT_ECN;
- opts.options &= info->options;
- if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
- synproxy_init_timestamp_cookie(info, &opts);
- else
- opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
- XT_SYNPROXY_OPT_SACK_PERM |
- XT_SYNPROXY_OPT_ECN);
- synproxy_send_client_synack(snet, skb, th, &opts);
- return NF_DROP;
- } else if (th->ack && !(th->fin || th->rst || th->syn)) {
- /* ACK from client */
- synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
- return NF_DROP;
- }
- return XT_CONTINUE;
- }
- static unsigned int ipv4_synproxy_hook(void *priv,
- struct sk_buff *skb,
- const struct nf_hook_state *nhs)
- {
- struct synproxy_net *snet = synproxy_pernet(nhs->net);
- enum ip_conntrack_info ctinfo;
- struct nf_conn *ct;
- struct nf_conn_synproxy *synproxy;
- struct synproxy_options opts = {};
- const struct ip_ct_tcp *state;
- struct tcphdr *th, _th;
- unsigned int thoff;
- ct = nf_ct_get(skb, &ctinfo);
- if (ct == NULL)
- return NF_ACCEPT;
- synproxy = nfct_synproxy(ct);
- if (synproxy == NULL)
- return NF_ACCEPT;
- if (nf_is_loopback_packet(skb))
- return NF_ACCEPT;
- thoff = ip_hdrlen(skb);
- th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
- if (th == NULL)
- return NF_DROP;
- state = &ct->proto.tcp;
- switch (state->state) {
- case TCP_CONNTRACK_CLOSE:
- if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
- nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
- ntohl(th->seq) + 1);
- break;
- }
- if (!th->syn || th->ack ||
- CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
- break;
- /* Reopened connection - reset the sequence number and timestamp
- * adjustments, they will get initialized once the connection is
- * reestablished.
- */
- nf_ct_seqadj_init(ct, ctinfo, 0);
- synproxy->tsoff = 0;
- this_cpu_inc(snet->stats->conn_reopened);
- /* fall through */
- case TCP_CONNTRACK_SYN_SENT:
- if (!synproxy_parse_options(skb, thoff, th, &opts))
- return NF_DROP;
- if (!th->syn && th->ack &&
- CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
- /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
- * therefore we need to add 1 to make the SYN sequence
- * number match the one of first SYN.
- */
- if (synproxy_recv_client_ack(snet, skb, th, &opts,
- ntohl(th->seq) + 1))
- this_cpu_inc(snet->stats->cookie_retrans);
- return NF_DROP;
- }
- synproxy->isn = ntohl(th->ack_seq);
- if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
- synproxy->its = opts.tsecr;
- break;
- case TCP_CONNTRACK_SYN_RECV:
- if (!th->syn || !th->ack)
- break;
- if (!synproxy_parse_options(skb, thoff, th, &opts))
- return NF_DROP;
- if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
- synproxy->tsoff = opts.tsval - synproxy->its;
- opts.options &= ~(XT_SYNPROXY_OPT_MSS |
- XT_SYNPROXY_OPT_WSCALE |
- XT_SYNPROXY_OPT_SACK_PERM);
- swap(opts.tsval, opts.tsecr);
- synproxy_send_server_ack(snet, state, skb, th, &opts);
- nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
- swap(opts.tsval, opts.tsecr);
- synproxy_send_client_ack(snet, skb, th, &opts);
- consume_skb(skb);
- return NF_STOLEN;
- default:
- break;
- }
- synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
- return NF_ACCEPT;
- }
- static int synproxy_tg4_check(const struct xt_tgchk_param *par)
- {
- const struct ipt_entry *e = par->entryinfo;
- if (e->ip.proto != IPPROTO_TCP ||
- e->ip.invflags & XT_INV_PROTO)
- return -EINVAL;
- return nf_ct_l3proto_try_module_get(par->family);
- }
- static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
- {
- nf_ct_l3proto_module_put(par->family);
- }
- static struct xt_target synproxy_tg4_reg __read_mostly = {
- .name = "SYNPROXY",
- .family = NFPROTO_IPV4,
- .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
- .target = synproxy_tg4,
- .targetsize = sizeof(struct xt_synproxy_info),
- .checkentry = synproxy_tg4_check,
- .destroy = synproxy_tg4_destroy,
- .me = THIS_MODULE,
- };
- static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
- {
- .hook = ipv4_synproxy_hook,
- .pf = NFPROTO_IPV4,
- .hooknum = NF_INET_LOCAL_IN,
- .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
- },
- {
- .hook = ipv4_synproxy_hook,
- .pf = NFPROTO_IPV4,
- .hooknum = NF_INET_POST_ROUTING,
- .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
- },
- };
- static int __init synproxy_tg4_init(void)
- {
- int err;
- err = nf_register_hooks(ipv4_synproxy_ops,
- ARRAY_SIZE(ipv4_synproxy_ops));
- if (err < 0)
- goto err1;
- err = xt_register_target(&synproxy_tg4_reg);
- if (err < 0)
- goto err2;
- return 0;
- err2:
- nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
- err1:
- return err;
- }
- static void __exit synproxy_tg4_exit(void)
- {
- xt_unregister_target(&synproxy_tg4_reg);
- nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
- }
- module_init(synproxy_tg4_init);
- module_exit(synproxy_tg4_exit);
- MODULE_LICENSE("GPL");
- MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
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