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