--- /dev/null
+/*
+ * 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 *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 = ntohs(htons(th->window) >> opts->wscale);
+ 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 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(dev_net(par->in));
+ 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(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(const struct nf_hook_ops *ops,
+ struct sk_buff *skb,
+ const struct nf_hook_state *nhs)
+{
+ struct synproxy_net *snet = synproxy_pernet(dev_net(nhs->in ? : nhs->out));
+ 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,
+ .owner = THIS_MODULE,
+ .pf = NFPROTO_IPV4,
+ .hooknum = NF_INET_LOCAL_IN,
+ .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+ },
+ {
+ .hook = ipv4_synproxy_hook,
+ .owner = THIS_MODULE,
+ .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>");
Code Review / kvmfornfv.git / blobdiff