// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (c) 2013 Patrick McHardy <[email protected]>
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/unaligned.h>
#include <net/tcp.h>
#include <net/netns/generic.h>
#include <linux/proc_fs.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter/nf_synproxy.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_extend.h>
#include <net/netfilter/nf_conntrack_seqadj.h>
#include <net/netfilter/nf_conntrack_synproxy.h>
#include <net/netfilter/nf_conntrack_zones.h>
#include <net/netfilter/nf_synproxy.h>
unsigned int synproxy_net_id;
EXPORT_SYMBOL_GPL(synproxy_net_id);
bool
synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
const struct tcphdr *th, struct synproxy_options *opts)
{
int length = (th->doff * 4) - sizeof(*th);
u8 buf[40], *ptr;
if (unlikely(length < 0))
return false;
ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf);
if (ptr == NULL)
return false;
opts->options = 0;
while (length > 0) {
int opcode = *ptr++;
int opsize;
switch (opcode) {
case TCPOPT_EOL:
return true;
case TCPOPT_NOP:
length--;
continue;
default:
if (length < 2)
return true;
opsize = *ptr++;
if (opsize < 2)
return true;
if (opsize > length)
return true;
switch (opcode) {
case TCPOPT_MSS:
if (opsize == TCPOLEN_MSS) {
opts->mss_option = get_unaligned_be16(ptr);
opts->options |= NF_SYNPROXY_OPT_MSS;
}
break;
case TCPOPT_WINDOW:
if (opsize == TCPOLEN_WINDOW) {
opts->wscale = *ptr;
if (opts->wscale > TCP_MAX_WSCALE)
opts->wscale = TCP_MAX_WSCALE;
opts->options |= NF_SYNPROXY_OPT_WSCALE;
}
break;
case TCPOPT_TIMESTAMP:
if (opsize == TCPOLEN_TIMESTAMP) {
opts->tsval = get_unaligned_be32(ptr);
opts->tsecr = get_unaligned_be32(ptr + 4);
opts->options |= NF_SYNPROXY_OPT_TIMESTAMP;
}
break;
case TCPOPT_SACK_PERM:
if (opsize == TCPOLEN_SACK_PERM)
opts->options |= NF_SYNPROXY_OPT_SACK_PERM;
break;
}
ptr += opsize - 2;
length -= opsize;
}
}
return true;
}
EXPORT_SYMBOL_GPL(synproxy_parse_options);
static unsigned int
synproxy_options_size(const struct synproxy_options *opts)
{
unsigned int size = 0;
if (opts->options & NF_SYNPROXY_OPT_MSS)
size += TCPOLEN_MSS_ALIGNED;
if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
size += TCPOLEN_TSTAMP_ALIGNED;
else if (opts->options & NF_SYNPROXY_OPT_SACK_PERM)
size += TCPOLEN_SACKPERM_ALIGNED;
if (opts->options & NF_SYNPROXY_OPT_WSCALE)
size += TCPOLEN_WSCALE_ALIGNED;
return size;
}
static void
synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts)
{
__be32 *ptr = (__be32 *)(th + 1);
u8 options = opts->options;
if (options & NF_SYNPROXY_OPT_MSS)
*ptr++ = htonl((TCPOPT_MSS << 24) |
(TCPOLEN_MSS << 16) |
opts->mss_option);
if (options & NF_SYNPROXY_OPT_TIMESTAMP) {
if (options & NF_SYNPROXY_OPT_SACK_PERM)
*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
(TCPOLEN_SACK_PERM << 16) |
(TCPOPT_TIMESTAMP << 8) |
TCPOLEN_TIMESTAMP);
else
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_NOP << 16) |
(TCPOPT_TIMESTAMP << 8) |
TCPOLEN_TIMESTAMP);
*ptr++ = htonl(opts->tsval);
*ptr++ = htonl(opts->tsecr);
} else if (options & NF_SYNPROXY_OPT_SACK_PERM)
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_NOP << 16) |
(TCPOPT_SACK_PERM << 8) |
TCPOLEN_SACK_PERM);
if (options & NF_SYNPROXY_OPT_WSCALE)
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_WINDOW << 16) |
(TCPOLEN_WINDOW << 8) |
opts->wscale);
}
void synproxy_init_timestamp_cookie(const struct nf_synproxy_info *info,
struct synproxy_options *opts)
{
opts->tsecr = opts->tsval;
opts->tsval = tcp_clock_ms() & ~0x3f;
if (opts->options & NF_SYNPROXY_OPT_WSCALE) {
opts->tsval |= opts->wscale;
opts->wscale = info->wscale;
} else
opts->tsval |= 0xf;
if (opts->options & NF_SYNPROXY_OPT_SACK_PERM)
opts->tsval |= 1 << 4;
if (opts->options & NF_SYNPROXY_OPT_ECN)
opts->tsval |= 1 << 5;
}
EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie);
static void
synproxy_check_timestamp_cookie(struct synproxy_options *opts)
{
opts->wscale = opts->tsecr & 0xf;
if (opts->wscale != 0xf)
opts->options |= NF_SYNPROXY_OPT_WSCALE;
opts->options |= opts->tsecr & (1 << 4) ? NF_SYNPROXY_OPT_SACK_PERM : 0;
opts->options |= opts->tsecr & (1 << 5) ? NF_SYNPROXY_OPT_ECN : 0;
}
static unsigned int
synproxy_tstamp_adjust(struct sk_buff *skb, unsigned int protoff,
struct tcphdr *th, struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
const struct nf_conn_synproxy *synproxy)
{
unsigned int optoff, optend;
__be32 *ptr, old;
if (synproxy->tsoff == 0)
return 1;
optoff = protoff + sizeof(struct tcphdr);
optend = protoff + th->doff * 4;
if (skb_ensure_writable(skb, optend))
return 0;
while (optoff < optend) {
unsigned char *op = skb->data + optoff;
switch (op[0]) {
case TCPOPT_EOL:
return 1;
case TCPOPT_NOP:
optoff++;
continue;
default:
if (optoff + 1 == optend ||
optoff + op[1] > optend ||
op[1] < 2)
return 0;
if (op[0] == TCPOPT_TIMESTAMP &&
op[1] == TCPOLEN_TIMESTAMP) {
if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY) {
ptr = (__be32 *)&op[2];
old = *ptr;
*ptr = htonl(ntohl(*ptr) -
synproxy->tsoff);
} else {
ptr = (__be32 *)&op[6];
old = *ptr;
*ptr = htonl(ntohl(*ptr) +
synproxy->tsoff);
}
inet_proto_csum_replace4(&th->check, skb,
old, *ptr, false);
return 1;
}
optoff += op[1];
}
}
return 1;
}
#ifdef CONFIG_PROC_FS
static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos)
{
struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
int cpu;
if (*pos == 0)
return SEQ_START_TOKEN;
for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) {
if (!cpu_possible(cpu))
continue;
*pos = cpu + 1;
return per_cpu_ptr(snet->stats, cpu);
}
return NULL;
}
static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
int cpu;
for (cpu = *pos; cpu < nr_cpu_ids; cpu++) {
if (!cpu_possible(cpu))
continue;
*pos = cpu + 1;
return per_cpu_ptr(snet->stats, cpu);
}
(*pos)++;
return NULL;
}
static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v)
{
return;
}
static int synproxy_cpu_seq_show(struct seq_file *seq, void *v)
{
struct synproxy_stats *stats = v;
if (v == SEQ_START_TOKEN) {
seq_puts(seq, "entries\t\tsyn_received\t"
"cookie_invalid\tcookie_valid\t"
"cookie_retrans\tconn_reopened\n");
return 0;
}
seq_printf(seq, "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0,
stats->syn_received,
stats->cookie_invalid,
stats->cookie_valid,
stats->cookie_retrans,
stats->conn_reopened);
return 0;
}
static const struct seq_operations synproxy_cpu_seq_ops = {
.start = synproxy_cpu_seq_start,
.next = synproxy_cpu_seq_next,
.stop = synproxy_cpu_seq_stop,
.show = synproxy_cpu_seq_show,
};
static int __net_init synproxy_proc_init(struct net *net)
{
if (!proc_create_net("synproxy", 0444, net->proc_net_stat,
&synproxy_cpu_seq_ops, sizeof(struct seq_net_private)))
return -ENOMEM;
return 0;
}
static void __net_exit synproxy_proc_exit(struct net *net)
{
remove_proc_entry("synproxy", net->proc_net_stat);
}
#else
static int __net_init synproxy_proc_init(struct net *net)
{
return 0;
}
static void __net_exit synproxy_proc_exit(struct net *net)
{
return;
}
#endif /* CONFIG_PROC_FS */
static int __net_init synproxy_net_init(struct net *net)
{
struct synproxy_net *snet = synproxy_pernet(net);
struct nf_conn *ct;
int err = -ENOMEM;
ct = nf_ct_tmpl_alloc(net, &nf_ct_zone_dflt, GFP_KERNEL);
if (!ct)
goto err1;
if (!nfct_seqadj_ext_add(ct))
goto err2;
if (!nfct_synproxy_ext_add(ct))
goto err2;
__set_bit(IPS_CONFIRMED_BIT, &ct->status);
snet->tmpl = ct;
snet->stats = alloc_percpu(struct synproxy_stats);
if (snet->stats == NULL)
goto err2;
err = synproxy_proc_init(net);
if (err < 0)
goto err3;
return 0;
err3:
free_percpu(snet->stats);
err2:
nf_ct_tmpl_free(ct);
err1:
return err;
}
static void __net_exit synproxy_net_exit(struct net *net)
{
struct synproxy_net *snet = synproxy_pernet(net);
nf_ct_put(snet->tmpl);
synproxy_proc_exit(net);
free_percpu(snet->stats);
}
static struct pernet_operations synproxy_net_ops = {
.init = synproxy_net_init,
.exit = synproxy_net_exit,
.id = &synproxy_net_id,
.size = sizeof(struct synproxy_net),
};
static int __init synproxy_core_init(void)
{
return register_pernet_subsys(&synproxy_net_ops);
}
static void __exit synproxy_core_exit(void)
{
unregister_pernet_subsys(&synproxy_net_ops);
}
module_init(synproxy_core_init);
module_exit(synproxy_core_exit);
static struct iphdr *
synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
__be32 daddr)
{
struct iphdr *iph;
skb_reset_network_header(skb);
iph = 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 = READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
iph->protocol = IPPROTO_TCP;
iph->check = 0;
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 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(net, nskb->sk, nskb, RTN_UNSPEC))
goto free_nskb;
if (nfct) {
nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
nf_conntrack_get(nfct);
}
ip_local_out(net, nskb->sk, nskb);
return;
free_nskb:
kfree_skb(nskb);
}
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 iphdr *iph, *niph;
struct tcphdr *nth;
unsigned int tcp_hdr_size;
u16 mss = opts->mss_encode;
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)
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_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 & NF_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);
}
EXPORT_SYMBOL_GPL(synproxy_send_client_synack);
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 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)
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 & NF_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 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)
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 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)
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);
}
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_v4_check(ip_hdr(skb), th);
if (mss == 0) {
this_cpu_inc(snet->stats->cookie_invalid);
return false;
}
this_cpu_inc(snet->stats->cookie_valid);
opts->mss_option = mss;
opts->options |= NF_SYNPROXY_OPT_MSS;
if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
synproxy_check_timestamp_cookie(opts);
synproxy_send_server_syn(net, skb, th, opts, recv_seq);
return true;
}
EXPORT_SYMBOL_GPL(synproxy_recv_client_ack);
unsigned int
ipv4_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;
unsigned int thoff;
ct = nf_ct_get(skb, &ctinfo);
if (!ct)
return NF_ACCEPT;
synproxy = nfct_synproxy(ct);
if (!synproxy)
return NF_ACCEPT;
if (nf_is_loopback_packet(skb) ||
ip_hdr(skb)->protocol != IPPROTO_TCP)
return NF_ACCEPT;
thoff = ip_hdrlen(skb);
th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
if (!th)
return NF_DROP;
state = &ct->proto.tcp;
switch (state->state) {
case TCP_CONNTRACK_CLOSE:
if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
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);
fallthrough;
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 & NF_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 & NF_SYNPROXY_OPT_TIMESTAMP) {
synproxy->tsoff = opts.tsval - synproxy->its;
nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
}
opts.options &= ~(NF_SYNPROXY_OPT_MSS |
NF_SYNPROXY_OPT_WSCALE |
NF_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;
}
EXPORT_SYMBOL_GPL(ipv4_synproxy_hook);
static const struct nf_hook_ops ipv4_synproxy_ops[] = {
{
.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,
},
};
int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net)
{
int err;
if (snet->hook_ref4 == 0) {
err = nf_register_net_hooks(net, ipv4_synproxy_ops,
ARRAY_SIZE(ipv4_synproxy_ops));
if (err)
return err;
}
snet->hook_ref4++;
return 0;
}
EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_init);
void nf_synproxy_ipv4_fini(struct synproxy_net *snet, struct net *net)
{
snet->hook_ref4--;
if (snet->hook_ref4 == 0)
nf_unregister_net_hooks(net, ipv4_synproxy_ops,
ARRAY_SIZE(ipv4_synproxy_ops));
}
EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_fini);
#if IS_ENABLED(CONFIG_IPV6)
static struct ipv6hdr *
synproxy_build_ip_ipv6(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 = READ_ONCE(net->ipv6.devconf_all->hop_limit);
iph->nexthdr = IPPROTO_TCP;
iph->saddr = *saddr;
iph->daddr = *daddr;
return iph;
}
static void
synproxy_send_tcp_ipv6(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;
int err;
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_common(&fl6));
err = nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
if (err) {
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);
}
void
synproxy_send_client_synack_ipv6(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_encode;
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)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip_ipv6(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(nf_ipv6_cookie_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 & NF_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_ipv6(net, skb, nskb, skb_nfct(skb),
IP_CT_ESTABLISHED_REPLY, niph, nth,
tcp_hdr_size);
}
EXPORT_SYMBOL_GPL(synproxy_send_client_synack_ipv6);
static void
synproxy_send_server_syn_ipv6(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)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip_ipv6(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 & NF_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_ipv6(net, skb, nskb, &snet->tmpl->ct_general,
IP_CT_NEW, niph, nth, tcp_hdr_size);
}
static void
synproxy_send_server_ack_ipv6(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)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip_ipv6(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_ipv6(net, skb, nskb, NULL, 0, niph, nth,
tcp_hdr_size);
}
static void
synproxy_send_client_ack_ipv6(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)
return;
skb_reserve(nskb, MAX_TCP_HEADER);
niph = synproxy_build_ip_ipv6(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_ipv6(net, skb, nskb, skb_nfct(skb),
IP_CT_ESTABLISHED_REPLY, niph, nth,
tcp_hdr_size);
}
bool
synproxy_recv_client_ack_ipv6(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 = nf_cookie_v6_check(ipv6_hdr(skb), th);
if (mss == 0) {
this_cpu_inc(snet->stats->cookie_invalid);
return false;
}
this_cpu_inc(snet->stats->cookie_valid);
opts->mss_option = mss;
opts->options |= NF_SYNPROXY_OPT_MSS;
if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
synproxy_check_timestamp_cookie(opts);
synproxy_send_server_syn_ipv6(net, skb, th, opts, recv_seq);
return true;
}
EXPORT_SYMBOL_GPL(synproxy_recv_client_ack_ipv6);
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)
return NF_ACCEPT;
synproxy = nfct_synproxy(ct);
if (!synproxy)
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)
return NF_DROP;
state = &ct->proto.tcp;
switch (state->state) {
case TCP_CONNTRACK_CLOSE:
if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
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);
fallthrough;
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_ipv6(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 & NF_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 & NF_SYNPROXY_OPT_TIMESTAMP) {
synproxy->tsoff = opts.tsval - synproxy->its;
nf_conntrack_event_cache(IPCT_SYNPROXY, ct);
}
opts.options &= ~(NF_SYNPROXY_OPT_MSS |
NF_SYNPROXY_OPT_WSCALE |
NF_SYNPROXY_OPT_SACK_PERM);
swap(opts.tsval, opts.tsecr);
synproxy_send_server_ack_ipv6(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_ipv6(net, skb, th, &opts);
consume_skb(skb);
return NF_STOLEN;
default:
break;
}
synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
return NF_ACCEPT;
}
EXPORT_SYMBOL_GPL(ipv6_synproxy_hook);
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,
},
};
int
nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net)
{
int err;
if (snet->hook_ref6 == 0) {
err = nf_register_net_hooks(net, ipv6_synproxy_ops,
ARRAY_SIZE(ipv6_synproxy_ops));
if (err)
return err;
}
snet->hook_ref6++;
return 0;
}
EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_init);
void
nf_synproxy_ipv6_fini(struct synproxy_net *snet, struct net *net)
{
snet->hook_ref6--;
if (snet->hook_ref6 == 0)
nf_unregister_net_hooks(net, ipv6_synproxy_ops,
ARRAY_SIZE(ipv6_synproxy_ops));
}
EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_fini);
#endif /* CONFIG_IPV6 */
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Patrick McHardy <[email protected]>");
MODULE_DESCRIPTION("nftables SYNPROXY expression support");
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