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 void
  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         BUG_ON(ptr == NULL);
  36
  37         opts->options = 0;
  38         while (length > 0) {
  39                 int opcode = *ptr++;
  40                 int opsize;
  41
  42                 switch (opcode) {
  43                 case TCPOPT_EOL:
  44                         return;
  45                 case TCPOPT_NOP:
  46                         length--;
  47                         continue;
  48                 default:
  49                         opsize = *ptr++;
  50                         if (opsize < 2)
  51                                 return;
  52                         if (opsize > length)
  53                                 return;
  54
  55                         switch (opcode) {
  56                         case TCPOPT_MSS:
  57                                 if (opsize == TCPOLEN_MSS) {
  58                                         opts->mss = get_unaligned_be16(ptr);
  59                                         opts->options |= XT_SYNPROXY_OPT_MSS;
  60                                 }
  61                                 break;
  62                         case TCPOPT_WINDOW:
  63                                 if (opsize == TCPOLEN_WINDOW) {
  64                                         opts->wscale = *ptr;
  65                                         if (opts->wscale > 14)
  66                                                 opts->wscale = 14;
  67                                         opts->options |= XT_SYNPROXY_OPT_WSCALE;
  68                                 }
  69                                 break;
  70                         case TCPOPT_TIMESTAMP:
  71                                 if (opsize == TCPOLEN_TIMESTAMP) {
  72                                         opts->tsval = get_unaligned_be32(ptr);
  73                                         opts->tsecr = get_unaligned_be32(ptr + 4);
  74                                         opts->options |= XT_SYNPROXY_OPT_TIMESTAMP;
  75                                 }
  76                                 break;
  77                         case TCPOPT_SACK_PERM:
  78                                 if (opsize == TCPOLEN_SACK_PERM)
  79                                         opts->options |= XT_SYNPROXY_OPT_SACK_PERM;
  80                                 break;
  81                         }
  82
  83                         ptr += opsize - 2;
  84                         length -= opsize;
  85                 }
  86         }
  87 }
  88 EXPORT_SYMBOL_GPL(synproxy_parse_options);
  89
  90 unsigned int synproxy_options_size(const struct synproxy_options *opts)
  91 {
  92         unsigned int size = 0;
  93
  94         if (opts->options & XT_SYNPROXY_OPT_MSS)
  95                 size += TCPOLEN_MSS_ALIGNED;
  96         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
  97                 size += TCPOLEN_TSTAMP_ALIGNED;
  98         else if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
  99                 size += TCPOLEN_SACKPERM_ALIGNED;
 100         if (opts->options & XT_SYNPROXY_OPT_WSCALE)
 101                 size += TCPOLEN_WSCALE_ALIGNED;
 102
 103         return size;
 104 }
 105 EXPORT_SYMBOL_GPL(synproxy_options_size);
 106
 107 void
 108 synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts)
 109 {
 110         __be32 *ptr = (__be32 *)(th + 1);
 111         u8 options = opts->options;
 112
 113         if (options & XT_SYNPROXY_OPT_MSS)
 114                 *ptr++ = htonl((TCPOPT_MSS << 24) |
 115                                (TCPOLEN_MSS << 16) |
 116                                opts->mss);
 117
 118         if (options & XT_SYNPROXY_OPT_TIMESTAMP) {
 119                 if (options & XT_SYNPROXY_OPT_SACK_PERM)
 120                         *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
 121                                        (TCPOLEN_SACK_PERM << 16) |
 122                                        (TCPOPT_TIMESTAMP << 8) |
 123                                        TCPOLEN_TIMESTAMP);
 124                 else
 125                         *ptr++ = htonl((TCPOPT_NOP << 24) |
 126                                        (TCPOPT_NOP << 16) |
 127                                        (TCPOPT_TIMESTAMP << 8) |
 128                                        TCPOLEN_TIMESTAMP);
 129
 130                 *ptr++ = htonl(opts->tsval);
 131                 *ptr++ = htonl(opts->tsecr);
 132         } else if (options & XT_SYNPROXY_OPT_SACK_PERM)
 133                 *ptr++ = htonl((TCPOPT_NOP << 24) |
 134                                (TCPOPT_NOP << 16) |
 135                                (TCPOPT_SACK_PERM << 8) |
 136                                TCPOLEN_SACK_PERM);
 137
 138         if (options & XT_SYNPROXY_OPT_WSCALE)
 139                 *ptr++ = htonl((TCPOPT_NOP << 24) |
 140                                (TCPOPT_WINDOW << 16) |
 141                                (TCPOLEN_WINDOW << 8) |
 142                                opts->wscale);
 143 }
 144 EXPORT_SYMBOL_GPL(synproxy_build_options);
 145
 146 void synproxy_init_timestamp_cookie(const struct xt_synproxy_info *info,
 147                                     struct synproxy_options *opts)
 148 {
 149         opts->tsecr = opts->tsval;
 150         opts->tsval = tcp_time_stamp & ~0x3f;
 151
 152         if (opts->options & XT_SYNPROXY_OPT_WSCALE)
 153                 opts->tsval |= info->wscale;
 154         else
 155                 opts->tsval |= 0xf;
 156
 157         if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
 158                 opts->tsval |= 1 << 4;
 159
 160         if (opts->options & XT_SYNPROXY_OPT_ECN)
 161                 opts->tsval |= 1 << 5;
 162 }
 163 EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie);
 164
 165 void synproxy_check_timestamp_cookie(struct synproxy_options *opts)
 166 {
 167         opts->wscale = opts->tsecr & 0xf;
 168         if (opts->wscale != 0xf)
 169                 opts->options |= XT_SYNPROXY_OPT_WSCALE;
 170
 171         opts->options |= opts->tsecr & (1 << 4) ? XT_SYNPROXY_OPT_SACK_PERM : 0;
 172
 173         opts->options |= opts->tsecr & (1 << 5) ? XT_SYNPROXY_OPT_ECN : 0;
 174 }
 175 EXPORT_SYMBOL_GPL(synproxy_check_timestamp_cookie);
 176
 177 unsigned int synproxy_tstamp_adjust(struct sk_buff *skb,
 178                                     unsigned int protoff,
 179                                     struct tcphdr *th,
 180                                     struct nf_conn *ct,
 181                                     enum ip_conntrack_info ctinfo,
 182                                     const struct nf_conn_synproxy *synproxy)
 183 {
 184         unsigned int optoff, optend;
 185         u32 *ptr, old;
 186
 187         if (synproxy->tsoff == 0)
 188                 return 1;
 189
 190         optoff = protoff + sizeof(struct tcphdr);
 191         optend = protoff + th->doff * 4;
 192
 193         if (!skb_make_writable(skb, optend))
 194                 return 0;
 195
 196         while (optoff < optend) {
 197                 unsigned char *op = skb->data + optoff;
 198
 199                 switch (op[0]) {
 200                 case TCPOPT_EOL:
 201                         return 1;
 202                 case TCPOPT_NOP:
 203                         optoff++;
 204                         continue;
 205                 default:
 206                         if (optoff + 1 == optend ||
 207                             optoff + op[1] > optend ||
 208                             op[1] < 2)
 209                                 return 0;
 210                         if (op[0] == TCPOPT_TIMESTAMP &&
 211                             op[1] == TCPOLEN_TIMESTAMP) {
 212                                 if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY) {
 213                                         ptr = (u32 *)&op[2];
 214                                         old = *ptr;
 215                                         *ptr = htonl(ntohl(*ptr) -
 216                                                      synproxy->tsoff);
 217                                 } else {
 218                                         ptr = (u32 *)&op[6];
 219                                         old = *ptr;
 220                                         *ptr = htonl(ntohl(*ptr) +
 221                                                      synproxy->tsoff);
 222                                 }
 223                                 inet_proto_csum_replace4(&th->check, skb,
 224                                                          old, *ptr, 0);
 225                                 return 1;
 226                         }
 227                         optoff += op[1];
 228                 }
 229         }
 230         return 1;
 231 }
 232 EXPORT_SYMBOL_GPL(synproxy_tstamp_adjust);
 233
 234 static struct nf_ct_ext_type nf_ct_synproxy_extend __read_mostly = {
 235         .len            = sizeof(struct nf_conn_synproxy),
 236         .align          = __alignof__(struct nf_conn_synproxy),
 237         .id             = NF_CT_EXT_SYNPROXY,
 238 };
 239
 240 #ifdef CONFIG_PROC_FS
 241 static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos)
 242 {
 243         struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
 244         int cpu;
 245
 246         if (*pos == 0)
 247                 return SEQ_START_TOKEN;
 248
 249         for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) {
 250                 if (!cpu_possible(cpu))
 251                         continue;
 252                 *pos = cpu + 1;
 253                 return per_cpu_ptr(snet->stats, cpu);
 254         }
 255
 256         return NULL;
 257 }
 258
 259 static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 260 {
 261         struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
 262         int cpu;
 263
 264         for (cpu = *pos; cpu < nr_cpu_ids; cpu++) {
 265                 if (!cpu_possible(cpu))
 266                         continue;
 267                 *pos = cpu + 1;
 268                 return per_cpu_ptr(snet->stats, cpu);
 269         }
 270
 271         return NULL;
 272 }
 273
 274 static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v)
 275 {
 276         return;
 277 }
 278
 279 static int synproxy_cpu_seq_show(struct seq_file *seq, void *v)
 280 {
 281         struct synproxy_stats *stats = v;
 282
 283         if (v == SEQ_START_TOKEN) {
 284                 seq_printf(seq, "entries\t\tsyn_received\t"
 285                                 "cookie_invalid\tcookie_valid\t"
 286                                 "cookie_retrans\tconn_reopened\n");
 287                 return 0;
 288         }
 289
 290         seq_printf(seq, "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0,
 291                    stats->syn_received,
 292                    stats->cookie_invalid,
 293                    stats->cookie_valid,
 294                    stats->cookie_retrans,
 295                    stats->conn_reopened);
 296
 297         return 0;
 298 }
 299
 300 static const struct seq_operations synproxy_cpu_seq_ops = {
 301         .start          = synproxy_cpu_seq_start,
 302         .next           = synproxy_cpu_seq_next,
 303         .stop           = synproxy_cpu_seq_stop,
 304         .show           = synproxy_cpu_seq_show,
 305 };
 306
 307 static int synproxy_cpu_seq_open(struct inode *inode, struct file *file)
 308 {
 309         return seq_open_net(inode, file, &synproxy_cpu_seq_ops,
 310                             sizeof(struct seq_net_private));
 311 }
 312
 313 static const struct file_operations synproxy_cpu_seq_fops = {
 314         .owner          = THIS_MODULE,
 315         .open           = synproxy_cpu_seq_open,
 316         .read           = seq_read,
 317         .llseek         = seq_lseek,
 318         .release        = seq_release_net,
 319 };
 320
 321 static int __net_init synproxy_proc_init(struct net *net)
 322 {
 323         if (!proc_create("synproxy", S_IRUGO, net->proc_net_stat,
 324                          &synproxy_cpu_seq_fops))
 325                 return -ENOMEM;
 326         return 0;
 327 }
 328
 329 static void __net_exit synproxy_proc_exit(struct net *net)
 330 {
 331         remove_proc_entry("synproxy", net->proc_net_stat);
 332 }
 333 #else
 334 static int __net_init synproxy_proc_init(struct net *net)
 335 {
 336         return 0;
 337 }
 338
 339 static void __net_exit synproxy_proc_exit(struct net *net)
 340 {
 341         return;
 342 }
 343 #endif /* CONFIG_PROC_FS */
 344
 345 static int __net_init synproxy_net_init(struct net *net)
 346 {
 347         struct synproxy_net *snet = synproxy_pernet(net);
 348         struct nf_conntrack_tuple t;
 349         struct nf_conn *ct;
 350         int err = -ENOMEM;
 351
 352         memset(&t, 0, sizeof(t));
 353         ct = nf_conntrack_alloc(net, 0, &t, &t, GFP_KERNEL);
 354         if (IS_ERR(ct)) {
 355                 err = PTR_ERR(ct);
 356                 goto err1;
 357         }
 358
 359         if (!nfct_seqadj_ext_add(ct))
 360                 goto err2;
 361         if (!nfct_synproxy_ext_add(ct))
 362                 goto err2;
 363         __set_bit(IPS_TEMPLATE_BIT, &ct->status);
 364         __set_bit(IPS_CONFIRMED_BIT, &ct->status);
 365
 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_conntrack_free(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>");