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
  21 #include <net/netfilter/nf_conntrack.h>
  22 #include <net/netfilter/nf_conntrack_extend.h>
  23 #include <net/netfilter/nf_conntrack_seqadj.h>
  24 #include <net/netfilter/nf_conntrack_synproxy.h>
  25 #include <net/netfilter/nf_conntrack_zones.h>
  26
  27 unsigned int synproxy_net_id;
  28 EXPORT_SYMBOL_GPL(synproxy_net_id);
  29
  30 bool
  31 synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
  32                        const struct tcphdr *th, struct synproxy_options *opts)
  33 {
  34         int length = (th->doff * 4) - sizeof(*th);
  35         u8 buf[40], *ptr;
  36
  37         ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf);
  38         if (ptr == NULL)
  39                 return false;
  40
  41         opts->options = 0;
  42         while (length > 0) {
  43                 int opcode = *ptr++;
  44                 int opsize;
  45
  46                 switch (opcode) {
  47                 case TCPOPT_EOL:
  48                         return true;
  49                 case TCPOPT_NOP:
  50                         length--;
  51                         continue;
  52                 default:
  53                         opsize = *ptr++;
  54                         if (opsize < 2)
  55                                 return true;
  56                         if (opsize > length)
  57                                 return true;
  58
  59                         switch (opcode) {
  60                         case TCPOPT_MSS:
  61                                 if (opsize == TCPOLEN_MSS) {
  62                                         opts->mss = get_unaligned_be16(ptr);
  63                                         opts->options |= XT_SYNPROXY_OPT_MSS;
  64                                 }
  65                                 break;
  66                         case TCPOPT_WINDOW:
  67                                 if (opsize == TCPOLEN_WINDOW) {
  68                                         opts->wscale = *ptr;
  69                                         if (opts->wscale > TCP_MAX_WSCALE)
  70                                                 opts->wscale = TCP_MAX_WSCALE;
  71                                         opts->options |= XT_SYNPROXY_OPT_WSCALE;
  72                                 }
  73                                 break;
  74                         case TCPOPT_TIMESTAMP:
  75                                 if (opsize == TCPOLEN_TIMESTAMP) {
  76                                         opts->tsval = get_unaligned_be32(ptr);
  77                                         opts->tsecr = get_unaligned_be32(ptr + 4);
  78                                         opts->options |= XT_SYNPROXY_OPT_TIMESTAMP;
  79                                 }
  80                                 break;
  81                         case TCPOPT_SACK_PERM:
  82                                 if (opsize == TCPOLEN_SACK_PERM)
  83                                         opts->options |= XT_SYNPROXY_OPT_SACK_PERM;
  84                                 break;
  85                         }
  86
  87                         ptr += opsize - 2;
  88                         length -= opsize;
  89                 }
  90         }
  91         return true;
  92 }
  93 EXPORT_SYMBOL_GPL(synproxy_parse_options);
  94
  95 unsigned int synproxy_options_size(const struct synproxy_options *opts)
  96 {
  97         unsigned int size = 0;
  98
  99         if (opts->options & XT_SYNPROXY_OPT_MSS)
 100                 size += TCPOLEN_MSS_ALIGNED;
 101         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
 102                 size += TCPOLEN_TSTAMP_ALIGNED;
 103         else if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
 104                 size += TCPOLEN_SACKPERM_ALIGNED;
 105         if (opts->options & XT_SYNPROXY_OPT_WSCALE)
 106                 size += TCPOLEN_WSCALE_ALIGNED;
 107
 108         return size;
 109 }
 110 EXPORT_SYMBOL_GPL(synproxy_options_size);
 111
 112 void
 113 synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts)
 114 {
 115         __be32 *ptr = (__be32 *)(th + 1);
 116         u8 options = opts->options;
 117
 118         if (options & XT_SYNPROXY_OPT_MSS)
 119                 *ptr++ = htonl((TCPOPT_MSS << 24) |
 120                                (TCPOLEN_MSS << 16) |
 121                                opts->mss);
 122
 123         if (options & XT_SYNPROXY_OPT_TIMESTAMP) {
 124                 if (options & XT_SYNPROXY_OPT_SACK_PERM)
 125                         *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
 126                                        (TCPOLEN_SACK_PERM << 16) |
 127                                        (TCPOPT_TIMESTAMP << 8) |
 128                                        TCPOLEN_TIMESTAMP);
 129                 else
 130                         *ptr++ = htonl((TCPOPT_NOP << 24) |
 131                                        (TCPOPT_NOP << 16) |
 132                                        (TCPOPT_TIMESTAMP << 8) |
 133                                        TCPOLEN_TIMESTAMP);
 134
 135                 *ptr++ = htonl(opts->tsval);
 136                 *ptr++ = htonl(opts->tsecr);
 137         } else if (options & XT_SYNPROXY_OPT_SACK_PERM)
 138                 *ptr++ = htonl((TCPOPT_NOP << 24) |
 139                                (TCPOPT_NOP << 16) |
 140                                (TCPOPT_SACK_PERM << 8) |
 141                                TCPOLEN_SACK_PERM);
 142
 143         if (options & XT_SYNPROXY_OPT_WSCALE)
 144                 *ptr++ = htonl((TCPOPT_NOP << 24) |
 145                                (TCPOPT_WINDOW << 16) |
 146                                (TCPOLEN_WINDOW << 8) |
 147                                opts->wscale);
 148 }
 149 EXPORT_SYMBOL_GPL(synproxy_build_options);
 150
 151 void synproxy_init_timestamp_cookie(const struct xt_synproxy_info *info,
 152                                     struct synproxy_options *opts)
 153 {
 154         opts->tsecr = opts->tsval;
 155         opts->tsval = tcp_time_stamp_raw() & ~0x3f;
 156
 157         if (opts->options & XT_SYNPROXY_OPT_WSCALE) {
 158                 opts->tsval |= opts->wscale;
 159                 opts->wscale = info->wscale;
 160         } else
 161                 opts->tsval |= 0xf;
 162
 163         if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
 164                 opts->tsval |= 1 << 4;
 165
 166         if (opts->options & XT_SYNPROXY_OPT_ECN)
 167                 opts->tsval |= 1 << 5;
 168 }
 169 EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie);
 170
 171 void synproxy_check_timestamp_cookie(struct synproxy_options *opts)
 172 {
 173         opts->wscale = opts->tsecr & 0xf;
 174         if (opts->wscale != 0xf)
 175                 opts->options |= XT_SYNPROXY_OPT_WSCALE;
 176
 177         opts->options |= opts->tsecr & (1 << 4) ? XT_SYNPROXY_OPT_SACK_PERM : 0;
 178
 179         opts->options |= opts->tsecr & (1 << 5) ? XT_SYNPROXY_OPT_ECN : 0;
 180 }
 181 EXPORT_SYMBOL_GPL(synproxy_check_timestamp_cookie);
 182
 183 unsigned int synproxy_tstamp_adjust(struct sk_buff *skb,
 184                                     unsigned int protoff,
 185                                     struct tcphdr *th,
 186                                     struct nf_conn *ct,
 187                                     enum ip_conntrack_info ctinfo,
 188                                     const struct nf_conn_synproxy *synproxy)
 189 {
 190         unsigned int optoff, optend;
 191         __be32 *ptr, old;
 192
 193         if (synproxy->tsoff == 0)
 194                 return 1;
 195
 196         optoff = protoff + sizeof(struct tcphdr);
 197         optend = protoff + th->doff * 4;
 198
 199         if (!skb_make_writable(skb, optend))
 200                 return 0;
 201
 202         while (optoff < optend) {
 203                 unsigned char *op = skb->data + optoff;
 204
 205                 switch (op[0]) {
 206                 case TCPOPT_EOL:
 207                         return 1;
 208                 case TCPOPT_NOP:
 209                         optoff++;
 210                         continue;
 211                 default:
 212                         if (optoff + 1 == optend ||
 213                             optoff + op[1] > optend ||
 214                             op[1] < 2)
 215                                 return 0;
 216                         if (op[0] == TCPOPT_TIMESTAMP &&
 217                             op[1] == TCPOLEN_TIMESTAMP) {
 218                                 if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY) {
 219                                         ptr = (__be32 *)&op[2];
 220                                         old = *ptr;
 221                                         *ptr = htonl(ntohl(*ptr) -
 222                                                      synproxy->tsoff);
 223                                 } else {
 224                                         ptr = (__be32 *)&op[6];
 225                                         old = *ptr;
 226                                         *ptr = htonl(ntohl(*ptr) +
 227                                                      synproxy->tsoff);
 228                                 }
 229                                 inet_proto_csum_replace4(&th->check, skb,
 230                                                          old, *ptr, false);
 231                                 return 1;
 232                         }
 233                         optoff += op[1];
 234                 }
 235         }
 236         return 1;
 237 }
 238 EXPORT_SYMBOL_GPL(synproxy_tstamp_adjust);
 239
 240 static struct nf_ct_ext_type nf_ct_synproxy_extend __read_mostly = {
 241         .len            = sizeof(struct nf_conn_synproxy),
 242         .align          = __alignof__(struct nf_conn_synproxy),
 243         .id             = NF_CT_EXT_SYNPROXY,
 244 };
 245
 246 #ifdef CONFIG_PROC_FS
 247 static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos)
 248 {
 249         struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
 250         int cpu;
 251
 252         if (*pos == 0)
 253                 return SEQ_START_TOKEN;
 254
 255         for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) {
 256                 if (!cpu_possible(cpu))
 257                         continue;
 258                 *pos = cpu + 1;
 259                 return per_cpu_ptr(snet->stats, cpu);
 260         }
 261
 262         return NULL;
 263 }
 264
 265 static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 266 {
 267         struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
 268         int cpu;
 269
 270         for (cpu = *pos; cpu < nr_cpu_ids; cpu++) {
 271                 if (!cpu_possible(cpu))
 272                         continue;
 273                 *pos = cpu + 1;
 274                 return per_cpu_ptr(snet->stats, cpu);
 275         }
 276
 277         return NULL;
 278 }
 279
 280 static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v)
 281 {
 282         return;
 283 }
 284
 285 static int synproxy_cpu_seq_show(struct seq_file *seq, void *v)
 286 {
 287         struct synproxy_stats *stats = v;
 288
 289         if (v == SEQ_START_TOKEN) {
 290                 seq_puts(seq, "entries\t\tsyn_received\t"
 291                               "cookie_invalid\tcookie_valid\t"
 292                               "cookie_retrans\tconn_reopened\n");
 293                 return 0;
 294         }
 295
 296         seq_printf(seq, "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0,
 297                    stats->syn_received,
 298                    stats->cookie_invalid,
 299                    stats->cookie_valid,
 300                    stats->cookie_retrans,
 301                    stats->conn_reopened);
 302
 303         return 0;
 304 }
 305
 306 static const struct seq_operations synproxy_cpu_seq_ops = {
 307         .start          = synproxy_cpu_seq_start,
 308         .next           = synproxy_cpu_seq_next,
 309         .stop           = synproxy_cpu_seq_stop,
 310         .show           = synproxy_cpu_seq_show,
 311 };
 312
 313 static int __net_init synproxy_proc_init(struct net *net)
 314 {
 315         if (!proc_create_net("synproxy", 0444, net->proc_net_stat,
 316                         &synproxy_cpu_seq_ops, sizeof(struct seq_net_private)))
 317                 return -ENOMEM;
 318         return 0;
 319 }
 320
 321 static void __net_exit synproxy_proc_exit(struct net *net)
 322 {
 323         remove_proc_entry("synproxy", net->proc_net_stat);
 324 }
 325 #else
 326 static int __net_init synproxy_proc_init(struct net *net)
 327 {
 328         return 0;
 329 }
 330
 331 static void __net_exit synproxy_proc_exit(struct net *net)
 332 {
 333         return;
 334 }
 335 #endif /* CONFIG_PROC_FS */
 336
 337 static int __net_init synproxy_net_init(struct net *net)
 338 {
 339         struct synproxy_net *snet = synproxy_pernet(net);
 340         struct nf_conn *ct;
 341         int err = -ENOMEM;
 342
 343         ct = nf_ct_tmpl_alloc(net, &nf_ct_zone_dflt, GFP_KERNEL);
 344         if (!ct)
 345                 goto err1;
 346
 347         if (!nfct_seqadj_ext_add(ct))
 348                 goto err2;
 349         if (!nfct_synproxy_ext_add(ct))
 350                 goto err2;
 351
 352         __set_bit(IPS_CONFIRMED_BIT, &ct->status);
 353         nf_conntrack_get(&ct->ct_general);
 354         snet->tmpl = ct;
 355
 356         snet->stats = alloc_percpu(struct synproxy_stats);
 357         if (snet->stats == NULL)
 358                 goto err2;
 359
 360         err = synproxy_proc_init(net);
 361         if (err < 0)
 362                 goto err3;
 363
 364         return 0;
 365
 366 err3:
 367         free_percpu(snet->stats);
 368 err2:
 369         nf_ct_tmpl_free(ct);
 370 err1:
 371         return err;
 372 }
 373
 374 static void __net_exit synproxy_net_exit(struct net *net)
 375 {
 376         struct synproxy_net *snet = synproxy_pernet(net);
 377
 378         nf_ct_put(snet->tmpl);
 379         synproxy_proc_exit(net);
 380         free_percpu(snet->stats);
 381 }
 382
 383 static struct pernet_operations synproxy_net_ops = {
 384         .init           = synproxy_net_init,
 385         .exit           = synproxy_net_exit,
 386         .id             = &synproxy_net_id,
 387         .size           = sizeof(struct synproxy_net),
 388 };
 389
 390 static int __init synproxy_core_init(void)
 391 {
 392         int err;
 393
 394         err = nf_ct_extend_register(&nf_ct_synproxy_extend);
 395         if (err < 0)
 396                 goto err1;
 397
 398         err = register_pernet_subsys(&synproxy_net_ops);
 399         if (err < 0)
 400                 goto err2;
 401
 402         return 0;
 403
 404 err2:
 405         nf_ct_extend_unregister(&nf_ct_synproxy_extend);
 406 err1:
 407         return err;
 408 }
 409
 410 static void __exit synproxy_core_exit(void)
 411 {
 412         unregister_pernet_subsys(&synproxy_net_ops);
 413         nf_ct_extend_unregister(&nf_ct_synproxy_extend);
 414 }
 415
 416 module_init(synproxy_core_init);
 417 module_exit(synproxy_core_exit);
 418
 419 MODULE_LICENSE("GPL");
 420 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");