net/ipv4/netfilter/ip_conntrack_ftp.c

   1 /* FTP extension for IP connection tracking. */
   2
   3 /* (C) 1999-2001 Paul `Rusty' Russell
   4  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10
  11 #include <linux/config.h>
  12 #include <linux/module.h>
  13 #include <linux/netfilter.h>
  14 #include <linux/ip.h>
  15 #include <linux/ctype.h>
  16 #include <net/checksum.h>
  17 #include <net/tcp.h>
  18
  19 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  20 #include <linux/netfilter_ipv4/ip_conntrack_ftp.h>
  21 #include <linux/moduleparam.h>
  22
  23 MODULE_LICENSE("GPL");
  24 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  25 MODULE_DESCRIPTION("ftp connection tracking helper");
  26
  27 /* This is slow, but it's simple. --RR */
  28 static char ftp_buffer[65536];
  29
  30 static DEFINE_SPINLOCK(ip_ftp_lock);
  31
  32 #define MAX_PORTS 8
  33 static int ports[MAX_PORTS];
  34 static int ports_c;
  35 module_param_array(ports, int, &ports_c, 0400);
  36
  37 static int loose;
  38 module_param(loose, int, 0600);
  39
  40 unsigned int (*ip_nat_ftp_hook)(struct sk_buff **pskb,
  41                                 enum ip_conntrack_info ctinfo,
  42                                 enum ip_ct_ftp_type type,
  43                                 unsigned int matchoff,
  44                                 unsigned int matchlen,
  45                                 struct ip_conntrack_expect *exp,
  46                                 u32 *seq);
  47 EXPORT_SYMBOL_GPL(ip_nat_ftp_hook);
  48
  49 #if 0
  50 #define DEBUGP printk
  51 #else
  52 #define DEBUGP(format, args...)
  53 #endif
  54
  55 static int try_rfc959(const char *, size_t, u_int32_t [], char);
  56 static int try_eprt(const char *, size_t, u_int32_t [], char);
  57 static int try_epsv_response(const char *, size_t, u_int32_t [], char);
  58
  59 static struct ftp_search {
  60         enum ip_conntrack_dir dir;
  61         const char *pattern;
  62         size_t plen;
  63         char skip;
  64         char term;
  65         enum ip_ct_ftp_type ftptype;
  66         int (*getnum)(const char *, size_t, u_int32_t[], char);
  67 } search[] = {
  68         {
  69                 IP_CT_DIR_ORIGINAL,
  70                 "PORT", sizeof("PORT") - 1, ' ', '\r',
  71                 IP_CT_FTP_PORT,
  72                 try_rfc959,
  73         },
  74         {
  75                 IP_CT_DIR_REPLY,
  76                 "227 ", sizeof("227 ") - 1, '(', ')',
  77                 IP_CT_FTP_PASV,
  78                 try_rfc959,
  79         },
  80         {
  81                 IP_CT_DIR_ORIGINAL,
  82                 "EPRT", sizeof("EPRT") - 1, ' ', '\r',
  83                 IP_CT_FTP_EPRT,
  84                 try_eprt,
  85         },
  86         {
  87                 IP_CT_DIR_REPLY,
  88                 "229 ", sizeof("229 ") - 1, '(', ')',
  89                 IP_CT_FTP_EPSV,
  90                 try_epsv_response,
  91         },
  92 };
  93
  94 static int try_number(const char *data, size_t dlen, u_int32_t array[],
  95                       int array_size, char sep, char term)
  96 {
  97         u_int32_t i, len;
  98
  99         memset(array, 0, sizeof(array[0])*array_size);
 100
 101         /* Keep data pointing at next char. */
 102         for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 103                 if (*data >= '0' && *data <= '9') {
 104                         array[i] = array[i]*10 + *data - '0';
 105                 }
 106                 else if (*data == sep)
 107                         i++;
 108                 else {
 109                         /* Unexpected character; true if it's the
 110                            terminator and we're finished. */
 111                         if (*data == term && i == array_size - 1)
 112                                 return len;
 113
 114                         DEBUGP("Char %u (got %u nums) `%u' unexpected\n",
 115                                len, i, *data);
 116                         return 0;
 117                 }
 118         }
 119         DEBUGP("Failed to fill %u numbers separated by %c\n", array_size, sep);
 120
 121         return 0;
 122 }
 123
 124 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 125 static int try_rfc959(const char *data, size_t dlen, u_int32_t array[6],
 126                        char term)
 127 {
 128         return try_number(data, dlen, array, 6, ',', term);
 129 }
 130
 131 /* Grab port: number up to delimiter */
 132 static int get_port(const char *data, int start, size_t dlen, char delim,
 133                     u_int32_t array[2])
 134 {
 135         u_int16_t port = 0;
 136         int i;
 137
 138         for (i = start; i < dlen; i++) {
 139                 /* Finished? */
 140                 if (data[i] == delim) {
 141                         if (port == 0)
 142                                 break;
 143                         array[0] = port >> 8;
 144                         array[1] = port;
 145                         return i + 1;
 146                 }
 147                 else if (data[i] >= '0' && data[i] <= '9')
 148                         port = port*10 + data[i] - '0';
 149                 else /* Some other crap */
 150                         break;
 151         }
 152         return 0;
 153 }
 154
 155 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| */
 156 static int try_eprt(const char *data, size_t dlen, u_int32_t array[6],
 157                     char term)
 158 {
 159         char delim;
 160         int length;
 161
 162         /* First character is delimiter, then "1" for IPv4, then
 163            delimiter again. */
 164         if (dlen <= 3) return 0;
 165         delim = data[0];
 166         if (isdigit(delim) || delim < 33 || delim > 126
 167             || data[1] != '1' || data[2] != delim)
 168                 return 0;
 169
 170         DEBUGP("EPRT: Got |1|!\n");
 171         /* Now we have IP address. */
 172         length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 173         if (length == 0)
 174                 return 0;
 175
 176         DEBUGP("EPRT: Got IP address!\n");
 177         /* Start offset includes initial "|1|", and trailing delimiter */
 178         return get_port(data, 3 + length + 1, dlen, delim, array+4);
 179 }
 180
 181 /* Returns 0, or length of numbers: |||6446| */
 182 static int try_epsv_response(const char *data, size_t dlen, u_int32_t array[6],
 183                              char term)
 184 {
 185         char delim;
 186
 187         /* Three delimiters. */
 188         if (dlen <= 3) return 0;
 189         delim = data[0];
 190         if (isdigit(delim) || delim < 33 || delim > 126
 191             || data[1] != delim || data[2] != delim)
 192                 return 0;
 193
 194         return get_port(data, 3, dlen, delim, array+4);
 195 }
 196
 197 /* Return 1 for match, 0 for accept, -1 for partial. */
 198 static int find_pattern(const char *data, size_t dlen,
 199                         const char *pattern, size_t plen,
 200                         char skip, char term,
 201                         unsigned int *numoff,
 202                         unsigned int *numlen,
 203                         u_int32_t array[6],
 204                         int (*getnum)(const char *, size_t, u_int32_t[], char))
 205 {
 206         size_t i;
 207
 208         DEBUGP("find_pattern `%s': dlen = %u\n", pattern, dlen);
 209         if (dlen == 0)
 210                 return 0;
 211
 212         if (dlen <= plen) {
 213                 /* Short packet: try for partial? */
 214                 if (strnicmp(data, pattern, dlen) == 0)
 215                         return -1;
 216                 else return 0;
 217         }
 218
 219         if (strnicmp(data, pattern, plen) != 0) {
 220 #if 0
 221                 size_t i;
 222
 223                 DEBUGP("ftp: string mismatch\n");
 224                 for (i = 0; i < plen; i++) {
 225                         DEBUGP("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
 226                                 i, data[i], data[i],
 227                                 pattern[i], pattern[i]);
 228                 }
 229 #endif
 230                 return 0;
 231         }
 232
 233         DEBUGP("Pattern matches!\n");
 234         /* Now we've found the constant string, try to skip
 235            to the 'skip' character */
 236         for (i = plen; data[i] != skip; i++)
 237                 if (i == dlen - 1) return -1;
 238
 239         /* Skip over the last character */
 240         i++;
 241
 242         DEBUGP("Skipped up to `%c'!\n", skip);
 243
 244         *numoff = i;
 245         *numlen = getnum(data + i, dlen - i, array, term);
 246         if (!*numlen)
 247                 return -1;
 248
 249         DEBUGP("Match succeeded!\n");
 250         return 1;
 251 }
 252
 253 /* Look up to see if we're just after a \n. */
 254 static int find_nl_seq(u32 seq, const struct ip_ct_ftp_master *info, int dir)
 255 {
 256         unsigned int i;
 257
 258         for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 259                 if (info->seq_aft_nl[dir][i] == seq)
 260                         return 1;
 261         return 0;
 262 }
 263
 264 /* We don't update if it's older than what we have. */
 265 static void update_nl_seq(u32 nl_seq, struct ip_ct_ftp_master *info, int dir)
 266 {
 267         unsigned int i, oldest = NUM_SEQ_TO_REMEMBER;
 268
 269         /* Look for oldest: if we find exact match, we're done. */
 270         for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 271                 if (info->seq_aft_nl[dir][i] == nl_seq)
 272                         return;
 273
 274                 if (oldest == info->seq_aft_nl_num[dir]
 275                     || before(info->seq_aft_nl[dir][i], oldest))
 276                         oldest = i;
 277         }
 278
 279         if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER)
 280                 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 281         else if (oldest != NUM_SEQ_TO_REMEMBER)
 282                 info->seq_aft_nl[dir][oldest] = nl_seq;
 283 }
 284
 285 static int help(struct sk_buff **pskb,
 286                 struct ip_conntrack *ct,
 287                 enum ip_conntrack_info ctinfo)
 288 {
 289         unsigned int dataoff, datalen;
 290         struct tcphdr _tcph, *th;
 291         char *fb_ptr;
 292         int ret;
 293         u32 seq, array[6] = { 0 };
 294         int dir = CTINFO2DIR(ctinfo);
 295         unsigned int matchlen, matchoff;
 296         struct ip_ct_ftp_master *ct_ftp_info = &ct->help.ct_ftp_info;
 297         struct ip_conntrack_expect *exp;
 298         unsigned int i;
 299         int found = 0, ends_in_nl;
 300
 301         /* Until there's been traffic both ways, don't look in packets. */
 302         if (ctinfo != IP_CT_ESTABLISHED
 303             && ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_REPLY) {
 304                 DEBUGP("ftp: Conntrackinfo = %u\n", ctinfo);
 305                 return NF_ACCEPT;
 306         }
 307
 308         th = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
 309                                 sizeof(_tcph), &_tcph);
 310         if (th == NULL)
 311                 return NF_ACCEPT;
 312
 313         dataoff = (*pskb)->nh.iph->ihl*4 + th->doff*4;
 314         /* No data? */
 315         if (dataoff >= (*pskb)->len) {
 316                 DEBUGP("ftp: pskblen = %u\n", (*pskb)->len);
 317                 return NF_ACCEPT;
 318         }
 319         datalen = (*pskb)->len - dataoff;
 320
 321         spin_lock_bh(&ip_ftp_lock);
 322         fb_ptr = skb_header_pointer(*pskb, dataoff,
 323                                     (*pskb)->len - dataoff, ftp_buffer);
 324         BUG_ON(fb_ptr == NULL);
 325
 326         ends_in_nl = (fb_ptr[datalen - 1] == '\n');
 327         seq = ntohl(th->seq) + datalen;
 328
 329         /* Look up to see if we're just after a \n. */
 330         if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
 331                 /* Now if this ends in \n, update ftp info. */
 332                 DEBUGP("ip_conntrack_ftp_help: wrong seq pos %s(%u) or %s(%u)\n",
 333                        ct_ftp_info->seq_aft_nl[0][dir]
 334                        old_seq_aft_nl_set ? "":"(UNSET) ", old_seq_aft_nl);
 335                 ret = NF_ACCEPT;
 336                 goto out_update_nl;
 337         }
 338
 339         /* Initialize IP array to expected address (it's not mentioned
 340            in EPSV responses) */
 341         array[0] = (ntohl(ct->tuplehash[dir].tuple.src.ip) >> 24) & 0xFF;
 342         array[1] = (ntohl(ct->tuplehash[dir].tuple.src.ip) >> 16) & 0xFF;
 343         array[2] = (ntohl(ct->tuplehash[dir].tuple.src.ip) >> 8) & 0xFF;
 344         array[3] = ntohl(ct->tuplehash[dir].tuple.src.ip) & 0xFF;
 345
 346         for (i = 0; i < ARRAY_SIZE(search); i++) {
 347                 if (search[i].dir != dir) continue;
 348
 349                 found = find_pattern(fb_ptr, (*pskb)->len - dataoff,
 350                                      search[i].pattern,
 351                                      search[i].plen,
 352                                      search[i].skip,
 353                                      search[i].term,
 354                                      &matchoff, &matchlen,
 355                                      array,
 356                                      search[i].getnum);
 357                 if (found) break;
 358         }
 359         if (found == -1) {
 360                 /* We don't usually drop packets.  After all, this is
 361                    connection tracking, not packet filtering.
 362                    However, it is necessary for accurate tracking in
 363                    this case. */
 364                 if (net_ratelimit())
 365                         printk("conntrack_ftp: partial %s %u+%u\n",
 366                                search[i].pattern,
 367                                ntohl(th->seq), datalen);
 368                 ret = NF_DROP;
 369                 goto out;
 370         } else if (found == 0) { /* No match */
 371                 ret = NF_ACCEPT;
 372                 goto out_update_nl;
 373         }
 374
 375         DEBUGP("conntrack_ftp: match `%s' (%u bytes at %u)\n",
 376                fb_ptr + matchoff, matchlen, ntohl(th->seq) + matchoff);
 377
 378         /* Allocate expectation which will be inserted */
 379         exp = ip_conntrack_expect_alloc(ct);
 380         if (exp == NULL) {
 381                 ret = NF_DROP;
 382                 goto out;
 383         }
 384
 385         /* We refer to the reverse direction ("!dir") tuples here,
 386          * because we're expecting something in the other direction.
 387          * Doesn't matter unless NAT is happening.  */
 388         exp->tuple.dst.ip = ct->tuplehash[!dir].tuple.dst.ip;
 389
 390         if (htonl((array[0] << 24) | (array[1] << 16) | (array[2] << 8) | array[3])
 391             != ct->tuplehash[dir].tuple.src.ip) {
 392                 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 393                    server: it really wants us to connect to a
 394                    different IP address.  Simply don't record it for
 395                    NAT. */
 396                 DEBUGP("conntrack_ftp: NOT RECORDING: %u,%u,%u,%u != %u.%u.%u.%u\n",
 397                        array[0], array[1], array[2], array[3],
 398                        NIPQUAD(ct->tuplehash[dir].tuple.src.ip));
 399
 400                 /* Thanks to Cristiano Lincoln Mattos
 401                    <lincoln@cesar.org.br> for reporting this potential
 402                    problem (DMZ machines opening holes to internal
 403                    networks, or the packet filter itself). */
 404                 if (!loose) {
 405                         ret = NF_ACCEPT;
 406                         goto out_put_expect;
 407                 }
 408                 exp->tuple.dst.ip = htonl((array[0] << 24) | (array[1] << 16)
 409                                          | (array[2] << 8) | array[3]);
 410         }
 411
 412         exp->tuple.src.ip = ct->tuplehash[!dir].tuple.src.ip;
 413         exp->tuple.dst.u.tcp.port = htons(array[4] << 8 | array[5]);
 414         exp->tuple.src.u.tcp.port = 0; /* Don't care. */
 415         exp->tuple.dst.protonum = IPPROTO_TCP;
 416         exp->mask = ((struct ip_conntrack_tuple)
 417                 { { 0xFFFFFFFF, { 0 } },
 418                   { 0xFFFFFFFF, { .tcp = { 0xFFFF } }, 0xFF }});
 419
 420         exp->expectfn = NULL;
 421
 422         /* Now, NAT might want to mangle the packet, and register the
 423          * (possibly changed) expectation itself. */
 424         if (ip_nat_ftp_hook)
 425                 ret = ip_nat_ftp_hook(pskb, ctinfo, search[i].ftptype,
 426                                       matchoff, matchlen, exp, &seq);
 427         else {
 428                 /* Can't expect this?  Best to drop packet now. */
 429                 if (ip_conntrack_expect_related(exp) != 0)
 430                         ret = NF_DROP;
 431                 else
 432                         ret = NF_ACCEPT;
 433         }
 434
 435 out_put_expect:
 436         ip_conntrack_expect_put(exp);
 437
 438 out_update_nl:
 439         /* Now if this ends in \n, update ftp info.  Seq may have been
 440          * adjusted by NAT code. */
 441         if (ends_in_nl)
 442                 update_nl_seq(seq, ct_ftp_info,dir);
 443  out:
 444         spin_unlock_bh(&ip_ftp_lock);
 445         return ret;
 446 }
 447
 448 static struct ip_conntrack_helper ftp[MAX_PORTS];
 449 static char ftp_names[MAX_PORTS][10];
 450
 451 /* Not __exit: called from init() */
 452 static void fini(void)
 453 {
 454         int i;
 455         for (i = 0; i < ports_c; i++) {
 456                 DEBUGP("ip_ct_ftp: unregistering helper for port %d\n",
 457                                 ports[i]);
 458                 ip_conntrack_helper_unregister(&ftp[i]);
 459         }
 460 }
 461
 462 static int __init init(void)
 463 {
 464         int i, ret;
 465         char *tmpname;
 466
 467         if (ports_c == 0)
 468                 ports[ports_c++] = FTP_PORT;
 469
 470         for (i = 0; i < ports_c; i++) {
 471                 ftp[i].tuple.src.u.tcp.port = htons(ports[i]);
 472                 ftp[i].tuple.dst.protonum = IPPROTO_TCP;
 473                 ftp[i].mask.src.u.tcp.port = 0xFFFF;
 474                 ftp[i].mask.dst.protonum = 0xFF;
 475                 ftp[i].max_expected = 1;
 476                 ftp[i].timeout = 5 * 60; /* 5 minutes */
 477                 ftp[i].me = THIS_MODULE;
 478                 ftp[i].help = help;
 479
 480                 tmpname = &ftp_names[i][0];
 481                 if (ports[i] == FTP_PORT)
 482                         sprintf(tmpname, "ftp");
 483                 else
 484                         sprintf(tmpname, "ftp-%d", ports[i]);
 485                 ftp[i].name = tmpname;
 486
 487                 DEBUGP("ip_ct_ftp: registering helper for port %d\n",
 488                                 ports[i]);
 489                 ret = ip_conntrack_helper_register(&ftp[i]);
 490
 491                 if (ret) {
 492                         fini();
 493                         return ret;
 494                 }
 495         }
 496         return 0;
 497 }
 498
 499 module_init(init);
 500 module_exit(fini);