net/netfilter/nf_synproxy_core.c

   1 /*
   2  * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <asm/unaligned.h>
  12 #include <net/tcp.h>
  13 #include <net/netns/generic.h>
  14
  15 #include <linux/netfilter_ipv4/ip_tables.h>
  16 #include <linux/netfilter/x_tables.h>
  17 #include <linux/netfilter/xt_tcpudp.h>
  18 #include <linux/netfilter/xt_SYNPROXY.h>
  19 #include <net/netfilter/nf_conntrack.h>
  20 #include <net/netfilter/nf_conntrack_extend.h>
  21 #include <net/netfilter/nf_conntrack_seqadj.h>
  22 #include <net/netfilter/nf_conntrack_synproxy.h>
  23
  24 int synproxy_net_id;
  25 EXPORT_SYMBOL_GPL(synproxy_net_id);
  26
  27 bool
  28 synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
  29                        const struct tcphdr *th, struct synproxy_options *opts)
  30 {
  31         int length = (th->doff * 4) - sizeof(*th);
  32         u8 buf[40], *ptr;
  33
  34         ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf);
  35         if (ptr == NULL)
  36                 return false;
  37
  38         opts->options = 0;
  39         while (length > 0) {
  40                 int opcode = *ptr++;
  41                 int opsize;
  42
  43                 switch (opcode) {
  44                 case TCPOPT_EOL:
  45                         return true;
  46                 case TCPOPT_NOP:
  47                         length--;
  48                         continue;
  49                 default:
  50                         opsize = *ptr++;
  51                         if (opsize < 2)
  52                                 return true;
  53                         if (opsize > length)
  54                                 return true;
  55
  56                         switch (opcode) {
  57                         case TCPOPT_MSS:
  58                                 if (opsize == TCPOLEN_MSS) {
  59                                         opts->mss = get_unaligned_be16(ptr);
  60                                         opts->options |= XT_SYNPROXY_OPT_MSS;
  61                                 }
  62                                 break;
  63                         case TCPOPT_WINDOW:
  64                                 if (opsize == TCPOLEN_WINDOW) {
  65                                         opts->wscale = *ptr;
  66                                         if (opts->wscale > 14)
  67                                                 opts->wscale = 14;
  68                                         opts->options |= XT_SYNPROXY_OPT_WSCALE;
  69                                 }
  70                                 break;
  71                         case TCPOPT_TIMESTAMP:
  72                                 if (opsize == TCPOLEN_TIMESTAMP) {
  73                                         opts->tsval = get_unaligned_be32(ptr);
  74                                         opts->tsecr = get_unaligned_be32(ptr + 4);
  75                                         opts->options |= XT_SYNPROXY_OPT_TIMESTAMP;
  76                                 }
  77                                 break;
  78                         case TCPOPT_SACK_PERM:
  79                                 if (opsize == TCPOLEN_SACK_PERM)
  80                                         opts->options |= XT_SYNPROXY_OPT_SACK_PERM;
  81                                 break;
  82                         }
  83
  84                         ptr += opsize - 2;
  85                         length -= opsize;
  86                 }
  87         }
  88         return true;
  89 }
  90 EXPORT_SYMBOL_GPL(synproxy_parse_options);
  91
  92 unsigned int synproxy_options_size(const struct synproxy_options *opts)
  93 {
  94         unsigned int size = 0;
  95
  96         if (opts->options & XT_SYNPROXY_OPT_MSS)
  97                 size += TCPOLEN_MSS_ALIGNED;
  98         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
  99                 size += TCPOLEN_TSTAMP_ALIGNED;
 100         else if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
 101                 size += TCPOLEN_SACKPERM_ALIGNED;
 102         if (opts->options & XT_SYNPROXY_OPT_WSCALE)
 103                 size += TCPOLEN_WSCALE_ALIGNED;
 104
 105         return size;
 106 }
 107 EXPORT_SYMBOL_GPL(synproxy_options_size);
 108
 109 void
 110 synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts)
 111 {
 112         __be32 *ptr = (__be32 *)(th + 1);
 113         u8 options = opts->options;
 114
 115         if (options & XT_SYNPROXY_OPT_MSS)
 116                 *ptr++ = htonl((TCPOPT_MSS << 24) |
 117                                (TCPOLEN_MSS << 16) |
 118                                opts->mss);
 119
 120         if (options & XT_SYNPROXY_OPT_TIMESTAMP) {
 121                 if (options & XT_SYNPROXY_OPT_SACK_PERM)
 122                         *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
 123                                        (TCPOLEN_SACK_PERM << 16) |
 124                                        (TCPOPT_TIMESTAMP << 8) |
 125                                        TCPOLEN_TIMESTAMP);
 126                 else
 127                         *ptr++ = htonl((TCPOPT_NOP << 24) |
 128                                        (TCPOPT_NOP << 16) |
 129                                        (TCPOPT_TIMESTAMP << 8) |
 130                                        TCPOLEN_TIMESTAMP);
 131
 132                 *ptr++ = htonl(opts->tsval);
 133                 *ptr++ = htonl(opts->tsecr);
 134         } else if (options & XT_SYNPROXY_OPT_SACK_PERM)
 135                 *ptr++ = htonl((TCPOPT_NOP << 24) |
 136                                (TCPOPT_NOP << 16) |
 137                                (TCPOPT_SACK_PERM << 8) |
 138                                TCPOLEN_SACK_PERM);
 139
 140         if (options & XT_SYNPROXY_OPT_WSCALE)
 141                 *ptr++ = htonl((TCPOPT_NOP << 24) |
 142                                (TCPOPT_WINDOW << 16) |
 143                                (TCPOLEN_WINDOW << 8) |
 144                                opts->wscale);
 145 }
 146 EXPORT_SYMBOL_GPL(synproxy_build_options);
 147
 148 void synproxy_init_timestamp_cookie(const struct xt_synproxy_info *info,
 149                                     struct synproxy_options *opts)
 150 {
 151         opts->tsecr = opts->tsval;
 152         opts->tsval = tcp_time_stamp & ~0x3f;
 153
 154         if (opts->options & XT_SYNPROXY_OPT_WSCALE)
 155                 opts->tsval |= info->wscale;
 156         else
 157                 opts->tsval |= 0xf;
 158
 159         if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
 160                 opts->tsval |= 1 << 4;
 161
 162         if (opts->options & XT_SYNPROXY_OPT_ECN)
 163                 opts->tsval |= 1 << 5;
 164 }
 165 EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie);
 166
 167 void synproxy_check_timestamp_cookie(struct synproxy_options *opts)
 168 {
 169         opts->wscale = opts->tsecr & 0xf;
 170         if (opts->wscale != 0xf)
 171                 opts->options |= XT_SYNPROXY_OPT_WSCALE;
 172
 173         opts->options |= opts->tsecr & (1 << 4) ? XT_SYNPROXY_OPT_SACK_PERM : 0;
 174
 175         opts->options |= opts->tsecr & (1 << 5) ? XT_SYNPROXY_OPT_ECN : 0;
 176 }
 177 EXPORT_SYMBOL_GPL(synproxy_check_timestamp_cookie);
 178
 179 unsigned int synproxy_tstamp_adjust(struct sk_buff *skb,
 180                                     unsigned int protoff,
 181                                     struct tcphdr *th,
 182                                     struct nf_conn *ct,
 183                                     enum ip_conntrack_info ctinfo,
 184                                     const struct nf_conn_synproxy *synproxy)
 185 {
 186         unsigned int optoff, optend;
 187         u32 *ptr, old;
 188
 189         if (synproxy->tsoff == 0)
 190                 return 1;
 191
 192         optoff = protoff + sizeof(struct tcphdr);
 193         optend = protoff + th->doff * 4;
 194
 195         if (!skb_make_writable(skb, optend))
 196                 return 0;
 197
 198         while (optoff < optend) {
 199                 unsigned char *op = skb->data + optoff;
 200
 201                 switch (op[0]) {
 202                 case TCPOPT_EOL:
 203                         return 1;
 204                 case TCPOPT_NOP:
 205                         optoff++;
 206                         continue;
 207                 default:
 208                         if (optoff + 1 == optend ||
 209                             optoff + op[1] > optend ||
 210                             op[1] < 2)
 211                                 return 0;
 212                         if (op[0] == TCPOPT_TIMESTAMP &&
 213                             op[1] == TCPOLEN_TIMESTAMP) {
 214                                 if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY) {
 215                                         ptr = (u32 *)&op[2];
 216                                         old = *ptr;
 217                                         *ptr = htonl(ntohl(*ptr) -
 218                                                      synproxy->tsoff);
 219                                 } else {
 220                                         ptr = (u32 *)&op[6];
 221                                         old = *ptr;
 222                                         *ptr = htonl(ntohl(*ptr) +
 223                                                      synproxy->tsoff);
 224                                 }
 225                                 inet_proto_csum_replace4(&th->check, skb,
 226                                                          old, *ptr, 0);
 227                                 return 1;
 228                         }
 229                         optoff += op[1];
 230                 }
 231         }
 232         return 1;
 233 }
 234 EXPORT_SYMBOL_GPL(synproxy_tstamp_adjust);
 235
 236 static struct nf_ct_ext_type nf_ct_synproxy_extend __read_mostly = {
 237         .len            = sizeof(struct nf_conn_synproxy),
 238         .align          = __alignof__(struct nf_conn_synproxy),
 239         .id             = NF_CT_EXT_SYNPROXY,
 240 };
 241
 242 #ifdef CONFIG_PROC_FS
 243 static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos)
 244 {
 245         struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
 246         int cpu;
 247
 248         if (*pos == 0)
 249                 return SEQ_START_TOKEN;
 250
 251         for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) {
 252                 if (!cpu_possible(cpu))
 253                         continue;
 254                 *pos = cpu + 1;
 255                 return per_cpu_ptr(snet->stats, cpu);
 256         }
 257
 258         return NULL;
 259 }
 260
 261 static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 262 {
 263         struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
 264         int cpu;
 265
 266         for (cpu = *pos; cpu < nr_cpu_ids; cpu++) {
 267                 if (!cpu_possible(cpu))
 268                         continue;
 269                 *pos = cpu + 1;
 270                 return per_cpu_ptr(snet->stats, cpu);
 271         }
 272
 273         return NULL;
 274 }
 275
 276 static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v)
 277 {
 278         return;
 279 }
 280
 281 static int synproxy_cpu_seq_show(struct seq_file *seq, void *v)
 282 {
 283         struct synproxy_stats *stats = v;
 284
 285         if (v == SEQ_START_TOKEN) {
 286                 seq_printf(seq, "entries\t\tsyn_received\t"
 287                                 "cookie_invalid\tcookie_valid\t"
 288                                 "cookie_retrans\tconn_reopened\n");
 289                 return 0;
 290         }
 291
 292         seq_printf(seq, "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0,
 293                    stats->syn_received,
 294                    stats->cookie_invalid,
 295                    stats->cookie_valid,
 296                    stats->cookie_retrans,
 297                    stats->conn_reopened);
 298
 299         return 0;
 300 }
 301
 302 static const struct seq_operations synproxy_cpu_seq_ops = {
 303         .start          = synproxy_cpu_seq_start,
 304         .next           = synproxy_cpu_seq_next,
 305         .stop           = synproxy_cpu_seq_stop,
 306         .show           = synproxy_cpu_seq_show,
 307 };
 308
 309 static int synproxy_cpu_seq_open(struct inode *inode, struct file *file)
 310 {
 311         return seq_open_net(inode, file, &synproxy_cpu_seq_ops,
 312                             sizeof(struct seq_net_private));
 313 }
 314
 315 static const struct file_operations synproxy_cpu_seq_fops = {
 316         .owner          = THIS_MODULE,
 317         .open           = synproxy_cpu_seq_open,
 318         .read           = seq_read,
 319         .llseek         = seq_lseek,
 320         .release        = seq_release_net,
 321 };
 322
 323 static int __net_init synproxy_proc_init(struct net *net)
 324 {
 325         if (!proc_create("synproxy", S_IRUGO, net->proc_net_stat,
 326                          &synproxy_cpu_seq_fops))
 327                 return -ENOMEM;
 328         return 0;
 329 }
 330
 331 static void __net_exit synproxy_proc_exit(struct net *net)
 332 {
 333         remove_proc_entry("synproxy", net->proc_net_stat);
 334 }
 335 #else
 336 static int __net_init synproxy_proc_init(struct net *net)
 337 {
 338         return 0;
 339 }
 340
 341 static void __net_exit synproxy_proc_exit(struct net *net)
 342 {
 343         return;
 344 }
 345 #endif /* CONFIG_PROC_FS */
 346
 347 static int __net_init synproxy_net_init(struct net *net)
 348 {
 349         struct synproxy_net *snet = synproxy_pernet(net);
 350         struct nf_conntrack_tuple t;
 351         struct nf_conn *ct;
 352         int err = -ENOMEM;
 353
 354         memset(&t, 0, sizeof(t));
 355         ct = nf_conntrack_alloc(net, 0, &t, &t, GFP_KERNEL);
 356         if (IS_ERR(ct)) {
 357                 err = PTR_ERR(ct);
 358                 goto err1;
 359         }
 360
 361         if (!nfct_seqadj_ext_add(ct))
 362                 goto err2;
 363         if (!nfct_synproxy_ext_add(ct))
 364                 goto err2;
 365         __set_bit(IPS_TEMPLATE_BIT, &ct->status);
 366         __set_bit(IPS_CONFIRMED_BIT, &ct->status);
 367
 368         snet->tmpl = ct;
 369
 370         snet->stats = alloc_percpu(struct synproxy_stats);
 371         if (snet->stats == NULL)
 372                 goto err2;
 373
 374         err = synproxy_proc_init(net);
 375         if (err < 0)
 376                 goto err3;
 377
 378         return 0;
 379
 380 err3:
 381         free_percpu(snet->stats);
 382 err2:
 383         nf_conntrack_free(ct);
 384 err1:
 385         return err;
 386 }
 387
 388 static void __net_exit synproxy_net_exit(struct net *net)
 389 {
 390         struct synproxy_net *snet = synproxy_pernet(net);
 391
 392         nf_conntrack_free(snet->tmpl);
 393         synproxy_proc_exit(net);
 394         free_percpu(snet->stats);
 395 }
 396
 397 static struct pernet_operations synproxy_net_ops = {
 398         .init           = synproxy_net_init,
 399         .exit           = synproxy_net_exit,
 400         .id             = &synproxy_net_id,
 401         .size           = sizeof(struct synproxy_net),
 402 };
 403
 404 static int __init synproxy_core_init(void)
 405 {
 406         int err;
 407
 408         err = nf_ct_extend_register(&nf_ct_synproxy_extend);
 409         if (err < 0)
 410                 goto err1;
 411
 412         err = register_pernet_subsys(&synproxy_net_ops);
 413         if (err < 0)
 414                 goto err2;
 415
 416         return 0;
 417
 418 err2:
 419         nf_ct_extend_unregister(&nf_ct_synproxy_extend);
 420 err1:
 421         return err;
 422 }
 423
 424 static void __exit synproxy_core_exit(void)
 425 {
 426         unregister_pernet_subsys(&synproxy_net_ops);
 427         nf_ct_extend_unregister(&nf_ct_synproxy_extend);
 428 }
 429
 430 module_init(synproxy_core_init);
 431 module_exit(synproxy_core_exit);
 432
 433 MODULE_LICENSE("GPL");
 434 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");