| /* |
| * 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> |
| #include <net/netfilter/nf_conntrack_ecache.h> |
| |
| static struct ipv6hdr * |
| synproxy_build_ip(struct net *net, struct sk_buff *skb, |
| const struct in6_addr *saddr, |
| const struct in6_addr *daddr) |
| { |
| struct ipv6hdr *iph; |
| |
| skb_reset_network_header(skb); |
| iph = skb_put(skb, sizeof(*iph)); |
| ip6_flow_hdr(iph, 0, 0); |
| iph->hop_limit = net->ipv6.devconf_all->hop_limit; |
| iph->nexthdr = IPPROTO_TCP; |
| iph->saddr = *saddr; |
| iph->daddr = *daddr; |
| |
| return iph; |
| } |
| |
| static void |
| synproxy_send_tcp(struct net *net, |
| 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 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->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) { |
| nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo); |
| nf_conntrack_get(nfct); |
| } |
| |
| ip6_local_out(net, nskb->sk, nskb); |
| return; |
| |
| free_nskb: |
| kfree_skb(nskb); |
| } |
| |
| static void |
| synproxy_send_client_synack(struct net *net, |
| 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(net, nskb, &iph->daddr, &iph->saddr); |
| |
| skb_reset_transport_header(nskb); |
| nth = 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(net, skb, nskb, skb_nfct(skb), |
| IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size); |
| } |
| |
| static void |
| synproxy_send_server_syn(struct net *net, |
| const struct sk_buff *skb, const struct tcphdr *th, |
| const struct synproxy_options *opts, u32 recv_seq) |
| { |
| struct synproxy_net *snet = synproxy_pernet(net); |
| 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(net, nskb, &iph->saddr, &iph->daddr); |
| |
| skb_reset_transport_header(nskb); |
| nth = 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(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW, |
| niph, nth, tcp_hdr_size); |
| } |
| |
| static void |
| synproxy_send_server_ack(struct net *net, |
| 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(net, nskb, &iph->daddr, &iph->saddr); |
| |
| skb_reset_transport_header(nskb); |
| nth = 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(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); |
| } |
| |
| static void |
| synproxy_send_client_ack(struct net *net, |
| 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(net, nskb, &iph->saddr, &iph->daddr); |
| |
| skb_reset_transport_header(nskb); |
| nth = 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(net, skb, nskb, skb_nfct(skb), |
| IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size); |
| } |
| |
| static bool |
| synproxy_recv_client_ack(struct net *net, |
| const struct sk_buff *skb, const struct tcphdr *th, |
| struct synproxy_options *opts, u32 recv_seq) |
| { |
| struct synproxy_net *snet = synproxy_pernet(net); |
| 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; |
| opts->options |= XT_SYNPROXY_OPT_MSS; |
| |
| if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP) |
| synproxy_check_timestamp_cookie(opts); |
| |
| synproxy_send_server_syn(net, 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 net *net = xt_net(par); |
| struct synproxy_net *snet = synproxy_pernet(net); |
| struct synproxy_options opts = {}; |
| struct tcphdr *th, _th; |
| |
| if (nf_ip6_checksum(skb, xt_hooknum(par), 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(net, skb, th, &opts); |
| consume_skb(skb); |
| return NF_STOLEN; |
| |
| } else if (th->ack && !(th->fin || th->rst || th->syn)) { |
| /* ACK from client */ |
| if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) { |
| consume_skb(skb); |
| return NF_STOLEN; |
| } else { |
| return NF_DROP; |
| } |
| } |
| |
| return XT_CONTINUE; |
| } |
| |
| static unsigned int ipv6_synproxy_hook(void *priv, |
| struct sk_buff *skb, |
| const struct nf_hook_state *nhs) |
| { |
| struct net *net = nhs->net; |
| struct synproxy_net *snet = synproxy_pernet(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; |
| __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 || nexthdr != IPPROTO_TCP) |
| 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: |
| 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(net, skb, th, &opts, |
| ntohl(th->seq) + 1)) { |
| this_cpu_inc(snet->stats->cookie_retrans); |
| consume_skb(skb); |
| return NF_STOLEN; |
| } else { |
| return NF_DROP; |
| } |
| } |
| |
| synproxy->isn = ntohl(th->ack_seq); |
| if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) |
| synproxy->its = opts.tsecr; |
| |
| nf_conntrack_event_cache(IPCT_SYNPROXY, ct); |
| 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; |
| nf_conntrack_event_cache(IPCT_SYNPROXY, ct); |
| } |
| |
| opts.options &= ~(XT_SYNPROXY_OPT_MSS | |
| XT_SYNPROXY_OPT_WSCALE | |
| XT_SYNPROXY_OPT_SACK_PERM); |
| |
| swap(opts.tsval, opts.tsecr); |
| synproxy_send_server_ack(net, state, skb, th, &opts); |
| |
| nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); |
| nf_conntrack_event_cache(IPCT_SEQADJ, ct); |
| |
| swap(opts.tsval, opts.tsecr); |
| synproxy_send_client_ack(net, skb, th, &opts); |
| |
| consume_skb(skb); |
| return NF_STOLEN; |
| default: |
| break; |
| } |
| |
| synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); |
| return NF_ACCEPT; |
| } |
| |
| static const struct nf_hook_ops ipv6_synproxy_ops[] = { |
| { |
| .hook = ipv6_synproxy_hook, |
| .pf = NFPROTO_IPV6, |
| .hooknum = NF_INET_LOCAL_IN, |
| .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, |
| }, |
| { |
| .hook = ipv6_synproxy_hook, |
| .pf = NFPROTO_IPV6, |
| .hooknum = NF_INET_POST_ROUTING, |
| .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, |
| }, |
| }; |
| |
| static int synproxy_tg6_check(const struct xt_tgchk_param *par) |
| { |
| struct synproxy_net *snet = synproxy_pernet(par->net); |
| const struct ip6t_entry *e = par->entryinfo; |
| int err; |
| |
| if (!(e->ipv6.flags & IP6T_F_PROTO) || |
| e->ipv6.proto != IPPROTO_TCP || |
| e->ipv6.invflags & XT_INV_PROTO) |
| return -EINVAL; |
| |
| err = nf_ct_netns_get(par->net, par->family); |
| if (err) |
| return err; |
| |
| if (snet->hook_ref6 == 0) { |
| err = nf_register_net_hooks(par->net, ipv6_synproxy_ops, |
| ARRAY_SIZE(ipv6_synproxy_ops)); |
| if (err) { |
| nf_ct_netns_put(par->net, par->family); |
| return err; |
| } |
| } |
| |
| snet->hook_ref6++; |
| return err; |
| } |
| |
| static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par) |
| { |
| struct synproxy_net *snet = synproxy_pernet(par->net); |
| |
| snet->hook_ref6--; |
| if (snet->hook_ref6 == 0) |
| nf_unregister_net_hooks(par->net, ipv6_synproxy_ops, |
| ARRAY_SIZE(ipv6_synproxy_ops)); |
| nf_ct_netns_put(par->net, par->family); |
| } |
| |
| static struct xt_target synproxy_tg6_reg __read_mostly = { |
| .name = "SYNPROXY", |
| .family = NFPROTO_IPV6, |
| .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD), |
| .target = synproxy_tg6, |
| .targetsize = sizeof(struct xt_synproxy_info), |
| .checkentry = synproxy_tg6_check, |
| .destroy = synproxy_tg6_destroy, |
| .me = THIS_MODULE, |
| }; |
| |
| static int __init synproxy_tg6_init(void) |
| { |
| return xt_register_target(&synproxy_tg6_reg); |
| } |
| |
| static void __exit synproxy_tg6_exit(void) |
| { |
| xt_unregister_target(&synproxy_tg6_reg); |
| } |
| |
| module_init(synproxy_tg6_init); |
| module_exit(synproxy_tg6_exit); |
| |
| MODULE_LICENSE("GPL"); |
| MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>"); |