@@ -153,6 +153,19 @@ config IP6_NF_TARGET_REJECT
To compile it as a module, choose M here. If unsure, say N.
+config IP6_NF_TARGET_SYNPROXY
+ tristate "SYNPROXY target support"
+ depends on NF_CONNTRACK && NETFILTER_ADVANCED
+ select NETFILTER_SYNPROXY
+ select SYN_COOKIES
+ help
+ The SYNPROXY target allows you to intercept TCP connections and
+ establish them using syncookies before they are passed on to the
+ server. This allows to avoid conntrack and server resource usage
+ during SYN-flood attacks.
+
+ To compile it as a module, choose M here. If unsure, say N.
+
config IP6_NF_MANGLE
tristate "Packet mangling"
default m if NETFILTER_ADVANCED=n
@@ -37,3 +37,4 @@ obj-$(CONFIG_IP6_NF_MATCH_RT) += ip6t_rt.o
obj-$(CONFIG_IP6_NF_TARGET_MASQUERADE) += ip6t_MASQUERADE.o
obj-$(CONFIG_IP6_NF_TARGET_NPT) += ip6t_NPT.o
obj-$(CONFIG_IP6_NF_TARGET_REJECT) += ip6t_REJECT.o
+obj-$(CONFIG_IP6_NF_TARGET_SYNPROXY) += ip6t_SYNPROXY.o
new file mode 100644
@@ -0,0 +1,495 @@
+/*
+ * 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/ip6_checksum.h>
+#include <net/ip6_route.h>
+#include <net/tcp.h>
+
+#include <linux/netfilter_ipv6/ip6_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 ipv6hdr *
+synproxy_build_ip(struct sk_buff *skb, const struct in6_addr *saddr,
+ const struct in6_addr *daddr)
+{
+ struct ipv6hdr *iph;
+
+ skb_reset_network_header(skb);
+ iph = (struct ipv6hdr *)skb_put(skb, sizeof(*iph));
+ ip6_flow_hdr(iph, 0, 0);
+ iph->hop_limit = 64; //XXX
+ iph->nexthdr = IPPROTO_TCP;
+ 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 ipv6hdr *niph, struct tcphdr *nth,
+ unsigned int tcp_hdr_size)
+{
+ struct net *net = nf_ct_net((struct nf_conn *)nfct);
+ struct dst_entry *dst;
+ struct flowi6 fl6;
+
+ nth->check = ~tcp_v6_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);
+
+ memset(&fl6, 0, sizeof(fl6));
+ fl6.flowi6_proto = IPPROTO_TCP;
+ fl6.saddr = niph->saddr;
+ fl6.daddr = niph->daddr;
+ fl6.fl6_sport = nth->source;
+ fl6.fl6_dport = nth->dest;
+ security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
+ dst = ip6_route_output(net, NULL, &fl6);
+ if (dst == NULL || dst->error) {
+ dst_release(dst);
+ goto free_nskb;
+ }
+ dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
+ if (IS_ERR(dst))
+ goto free_nskb;
+
+ skb_dst_set(nskb, dst);
+
+ if (nfct) {
+ nskb->nfct = nfct;
+ nskb->nfctinfo = ctinfo;
+ nf_conntrack_get(nfct);
+ }
+
+ ip6_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 ipv6hdr *iph, *niph;
+ struct tcphdr *nth;
+ unsigned int tcp_hdr_size;
+ u16 mss = opts->mss;
+
+ iph = ipv6_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_v6_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 ipv6hdr *iph, *niph;
+ struct tcphdr *nth;
+ unsigned int tcp_hdr_size;
+
+ iph = ipv6_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 ipv6hdr *iph, *niph;
+ struct tcphdr *nth;
+ unsigned int tcp_hdr_size;
+
+ iph = ipv6_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 ipv6hdr *iph, *niph;
+ struct tcphdr *nth;
+ unsigned int tcp_hdr_size;
+
+ iph = ipv6_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_v6_check(ipv6_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;
+
+ 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_tg6(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_ip6_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;
+
+ synproxy_parse_options(skb, par->thoff, th, &opts);
+
+ if (th->syn) {
+ /* 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);
+ } else if (th->ack && !(th->fin || th->rst))
+ /* ACK from client */
+ synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
+
+ return NF_DROP;
+}
+
+static unsigned int ipv6_synproxy_hook(unsigned int hooknum,
+ struct sk_buff *skb,
+ const struct net_device *in,
+ const struct net_device *out,
+ int (*okfn)(struct sk_buff *))
+{
+ struct synproxy_net *snet = synproxy_pernet(dev_net(in ? : 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;
+ __be16 frag_off;
+ u8 nexthdr;
+ 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;
+
+ nexthdr = ipv6_hdr(skb)->nexthdr;
+ thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
+ &frag_off);
+ if (thoff < 0)
+ return NF_ACCEPT;
+
+ 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:
+ synproxy_parse_options(skb, thoff, th, &opts);
+
+ 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;
+
+ synproxy_parse_options(skb, thoff, th, &opts);
+ 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_tg6_check(const struct xt_tgchk_param *par)
+{
+ const struct ip6t_entry *e = par->entryinfo;
+
+ if (!(e->ipv6.flags & IP6T_F_PROTO) ||
+ e->ipv6.proto != IPPROTO_TCP ||
+ e->ipv6.invflags & XT_INV_PROTO)
+ return -EINVAL;
+
+ return nf_ct_l3proto_try_module_get(par->family);
+}
+
+static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
+{
+ nf_ct_l3proto_module_put(par->family);
+}
+
+static struct xt_target synproxy_tg6_reg __read_mostly = {
+ .name = "SYNPROXY",
+ .family = NFPROTO_IPV6,
+ .target = synproxy_tg6,
+ .targetsize = sizeof(struct xt_synproxy_info),
+ .checkentry = synproxy_tg6_check,
+ .destroy = synproxy_tg6_destroy,
+ .me = THIS_MODULE,
+};
+
+static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
+ {
+ .hook = ipv6_synproxy_hook,
+ .owner = THIS_MODULE,
+ .pf = NFPROTO_IPV6,
+ .hooknum = NF_INET_LOCAL_IN,
+ .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+ },
+ {
+ .hook = ipv6_synproxy_hook,
+ .owner = THIS_MODULE,
+ .pf = NFPROTO_IPV6,
+ .hooknum = NF_INET_POST_ROUTING,
+ .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
+ },
+};
+
+static int __init synproxy_tg6_init(void)
+{
+ int err;
+
+ err = nf_register_hooks(ipv6_synproxy_ops,
+ ARRAY_SIZE(ipv6_synproxy_ops));
+ if (err < 0)
+ goto err1;
+
+ err = xt_register_target(&synproxy_tg6_reg);
+ if (err < 0)
+ goto err2;
+
+ return 0;
+
+err2:
+ nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
+err1:
+ return err;
+}
+
+static void __exit synproxy_tg6_exit(void)
+{
+ xt_unregister_target(&synproxy_tg6_reg);
+ nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
+}
+
+module_init(synproxy_tg6_init);
+module_exit(synproxy_tg6_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
Add an IPv6 version of the SYNPROXY target. The main differences to the IPv4 version is routing and IP header construction. Signed-off-by: Patrick McHardy <kaber@trash.net> --- net/ipv6/netfilter/Kconfig | 13 + net/ipv6/netfilter/Makefile | 1 + net/ipv6/netfilter/ip6t_SYNPROXY.c | 495 +++++++++++++++++++++++++++++++++++++ 3 files changed, 509 insertions(+) create mode 100644 net/ipv6/netfilter/ip6t_SYNPROXY.c