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/lockhelp.h>
  20 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  21 #include <linux/netfilter_ipv4/ip_conntrack_ftp.h>
  22 #include <linux/moduleparam.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  26 MODULE_DESCRIPTION("ftp connection tracking helper");
  27
  28 /* This is slow, but it's simple. --RR */
  29 static char ftp_buffer[65536];
  30
  31 static DECLARE_LOCK(ip_ftp_lock);
  32
  33 #define MAX_PORTS 8
  34 static int ports[MAX_PORTS];
  35 static int ports_c;
  36 module_param_array(ports, int, &ports_c, 0400);
  37
  38 static int loose;
  39 module_param(loose, int, 0600);
  40
  41 unsigned int (*ip_nat_ftp_hook)(struct sk_buff **pskb,
  42                                 enum ip_conntrack_info ctinfo,
  43                                 enum ip_ct_ftp_type type,
  44                                 unsigned int matchoff,
  45                                 unsigned int matchlen,
  46                                 struct ip_conntrack_expect *exp,
  47                                 u32 *seq);
  48 EXPORT_SYMBOL_GPL(ip_nat_ftp_hook);
  49
  50 #if 0
  51 #define DEBUGP printk
  52 #else
  53 #define DEBUGP(format, args...)
  54 #endif
  55
  56 static int try_rfc959(const char *, size_t, u_int32_t [], char);
  57 static int try_eprt(const char *, size_t, u_int32_t [], char);
  58 static int try_epsv_response(const char *, size_t, u_int32_t [], char);
  59
  60 static struct ftp_search {
  61         enum ip_conntrack_dir dir;
  62         const char *pattern;
  63         size_t plen;
  64         char skip;
  65         char term;
  66         enum ip_ct_ftp_type ftptype;
  67         int (*getnum)(const char *, size_t, u_int32_t[], char);
  68 } search[] = {
  69         {
  70                 IP_CT_DIR_ORIGINAL,
  71                 "PORT", sizeof("PORT") - 1, ' ', '\r',
  72                 IP_CT_FTP_PORT,
  73                 try_rfc959,
  74         },
  75         {
  76                 IP_CT_DIR_REPLY,
  77                 "227 ", sizeof("227 ") - 1, '(', ')',
  78                 IP_CT_FTP_PASV,
  79                 try_rfc959,
  80         },
  81         {
  82                 IP_CT_DIR_ORIGINAL,
  83                 "EPRT", sizeof("EPRT") - 1, ' ', '\r',
  84                 IP_CT_FTP_EPRT,
  85                 try_eprt,
  86         },
  87         {
  88                 IP_CT_DIR_REPLY,
  89                 "229 ", sizeof("229 ") - 1, '(', ')',
  90                 IP_CT_FTP_EPSV,
  91                 try_epsv_response,
  92         },
  93 };
  94
  95 static int try_number(const char *data, size_t dlen, u_int32_t array[],
  96                       int array_size, char sep, char term)
  97 {
  98         u_int32_t i, len;
  99
 100         memset(array, 0, sizeof(array[0])*array_size);
 101
 102         /* Keep data pointing at next char. */
 103         for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 104                 if (*data >= '0' && *data <= '9') {
 105                         array[i] = array[i]*10 + *data - '0';
 106                 }
 107                 else if (*data == sep)
 108                         i++;
 109                 else {
 110                         /* Unexpected character; true if it's the
 111                            terminator and we're finished. */
 112                         if (*data == term && i == array_size - 1)
 113                                 return len;
 114
 115                         DEBUGP("Char %u (got %u nums) `%u' unexpected\n",
 116                                len, i, *data);
 117                         return 0;
 118                 }
 119         }
 120         DEBUGP("Failed to fill %u numbers separated by %c\n", array_size, sep);
 121
 122         return 0;
 123 }
 124
 125 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 126 static int try_rfc959(const char *data, size_t dlen, u_int32_t array[6],
 127                        char term)
 128 {
 129         return try_number(data, dlen, array, 6, ',', term);
 130 }
 131
 132 /* Grab port: number up to delimiter */
 133 static int get_port(const char *data, int start, size_t dlen, char delim,
 134                     u_int32_t array[2])
 135 {
 136         u_int16_t port = 0;
 137         int i;
 138
 139         for (i = start; i < dlen; i++) {
 140                 /* Finished? */
 141                 if (data[i] == delim) {
 142                         if (port == 0)
 143                                 break;
 144                         array[0] = port >> 8;
 145                         array[1] = port;
 146                         return i + 1;
 147                 }
 148                 else if (data[i] >= '0' && data[i] <= '9')
 149                         port = port*10 + data[i] - '0';
 150                 else /* Some other crap */
 151                         break;
 152         }
 153         return 0;
 154 }
 155
 156 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| */
 157 static int try_eprt(const char *data, size_t dlen, u_int32_t array[6],
 158                     char term)
 159 {
 160         char delim;
 161         int length;
 162
 163         /* First character is delimiter, then "1" for IPv4, then
 164            delimiter again. */
 165         if (dlen <= 3) return 0;
 166         delim = data[0];
 167         if (isdigit(delim) || delim < 33 || delim > 126
 168             || data[1] != '1' || data[2] != delim)
 169                 return 0;
 170
 171         DEBUGP("EPRT: Got |1|!\n");
 172         /* Now we have IP address. */
 173         length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 174         if (length == 0)
 175                 return 0;
 176
 177         DEBUGP("EPRT: Got IP address!\n");
 178         /* Start offset includes initial "|1|", and trailing delimiter */
 179         return get_port(data, 3 + length + 1, dlen, delim, array+4);
 180 }
 181
 182 /* Returns 0, or length of numbers: |||6446| */
 183 static int try_epsv_response(const char *data, size_t dlen, u_int32_t array[6],
 184                              char term)
 185 {
 186         char delim;
 187
 188         /* Three delimiters. */
 189         if (dlen <= 3) return 0;
 190         delim = data[0];
 191         if (isdigit(delim) || delim < 33 || delim > 126
 192             || data[1] != delim || data[2] != delim)
 193                 return 0;
 194
 195         return get_port(data, 3, dlen, delim, array+4);
 196 }
 197
 198 /* Return 1 for match, 0 for accept, -1 for partial. */
 199 static int find_pattern(const char *data, size_t dlen,
 200                         const char *pattern, size_t plen,
 201                         char skip, char term,
 202                         unsigned int *numoff,
 203                         unsigned int *numlen,
 204                         u_int32_t array[6],
 205                         int (*getnum)(const char *, size_t, u_int32_t[], char))
 206 {
 207         size_t i;
 208
 209         DEBUGP("find_pattern `%s': dlen = %u\n", pattern, dlen);
 210         if (dlen == 0)
 211                 return 0;
 212
 213         if (dlen <= plen) {
 214                 /* Short packet: try for partial? */
 215                 if (strnicmp(data, pattern, dlen) == 0)
 216                         return -1;
 217                 else return 0;
 218         }
 219
 220         if (strnicmp(data, pattern, plen) != 0) {
 221 #if 0
 222                 size_t i;
 223
 224                 DEBUGP("ftp: string mismatch\n");
 225                 for (i = 0; i < plen; i++) {
 226                         DEBUGP("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
 227                                 i, data[i], data[i],
 228                                 pattern[i], pattern[i]);
 229                 }
 230 #endif
 231                 return 0;
 232         }
 233
 234         DEBUGP("Pattern matches!\n");
 235         /* Now we've found the constant string, try to skip
 236            to the 'skip' character */
 237         for (i = plen; data[i] != skip; i++)
 238                 if (i == dlen - 1) return -1;
 239
 240         /* Skip over the last character */
 241         i++;
 242
 243         DEBUGP("Skipped up to `%c'!\n", skip);
 244
 245         *numoff = i;
 246         *numlen = getnum(data + i, dlen - i, array, term);
 247         if (!*numlen)
 248                 return -1;
 249
 250         DEBUGP("Match succeeded!\n");
 251         return 1;
 252 }
 253
 254 /* Look up to see if we're just after a \n. */
 255 static int find_nl_seq(u16 seq, const struct ip_ct_ftp_master *info, int dir)
 256 {
 257         unsigned int i;
 258
 259         for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 260                 if (info->seq_aft_nl[dir][i] == seq)
 261                         return 1;
 262         return 0;
 263 }
 264
 265 /* We don't update if it's older than what we have. */
 266 static void update_nl_seq(u16 nl_seq, struct ip_ct_ftp_master *info, int dir)
 267 {
 268         unsigned int i, oldest = NUM_SEQ_TO_REMEMBER;
 269
 270         /* Look for oldest: if we find exact match, we're done. */
 271         for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 272                 if (info->seq_aft_nl[dir][i] == nl_seq)
 273                         return;
 274
 275                 if (oldest == info->seq_aft_nl_num[dir]
 276                     || before(info->seq_aft_nl[dir][i], oldest))
 277                         oldest = i;
 278         }
 279
 280         if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER)
 281                 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 282         else if (oldest != NUM_SEQ_TO_REMEMBER)
 283                 info->seq_aft_nl[dir][oldest] = nl_seq;
 284 }
 285
 286 static int help(struct sk_buff **pskb,
 287                 struct ip_conntrack *ct,
 288                 enum ip_conntrack_info ctinfo)
 289 {
 290         unsigned int dataoff, datalen;
 291         struct tcphdr _tcph, *th;
 292         char *fb_ptr;
 293         int ret;
 294         u32 seq, array[6] = { 0 };
 295         int dir = CTINFO2DIR(ctinfo);
 296         unsigned int matchlen, matchoff;
 297         struct ip_ct_ftp_master *ct_ftp_info = &ct->help.ct_ftp_info;
 298         struct ip_conntrack_expect *exp;
 299         unsigned int i;
 300         int found = 0, ends_in_nl;
 301
 302         /* Until there's been traffic both ways, don't look in packets. */
 303         if (ctinfo != IP_CT_ESTABLISHED
 304             && ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_REPLY) {
 305                 DEBUGP("ftp: Conntrackinfo = %u\n", ctinfo);
 306                 return NF_ACCEPT;
 307         }
 308
 309         th = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
 310                                 sizeof(_tcph), &_tcph);
 311         if (th == NULL)
 312                 return NF_ACCEPT;
 313
 314         dataoff = (*pskb)->nh.iph->ihl*4 + th->doff*4;
 315         /* No data? */
 316         if (dataoff >= (*pskb)->len) {
 317                 DEBUGP("ftp: pskblen = %u\n", (*pskb)->len);
 318                 return NF_ACCEPT;
 319         }
 320         datalen = (*pskb)->len - dataoff;
 321
 322         LOCK_BH(&ip_ftp_lock);
 323         fb_ptr = skb_header_pointer(*pskb, dataoff,
 324                                     (*pskb)->len - dataoff, ftp_buffer);
 325         BUG_ON(fb_ptr == NULL);
 326
 327         ends_in_nl = (fb_ptr[datalen - 1] == '\n');
 328         seq = ntohl(th->seq) + datalen;
 329
 330         /* Look up to see if we're just after a \n. */
 331         if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
 332                 /* Now if this ends in \n, update ftp info. */
 333                 DEBUGP("ip_conntrack_ftp_help: wrong seq pos %s(%u) or %s(%u)\n",
 334                        ct_ftp_info->seq_aft_nl[0][dir]
 335                        old_seq_aft_nl_set ? "":"(UNSET) ", old_seq_aft_nl);
 336                 ret = NF_ACCEPT;
 337                 goto out_update_nl;
 338         }
 339
 340         /* Initialize IP array to expected address (it's not mentioned
 341            in EPSV responses) */
 342         array[0] = (ntohl(ct->tuplehash[dir].tuple.src.ip) >> 24) & 0xFF;
 343         array[1] = (ntohl(ct->tuplehash[dir].tuple.src.ip) >> 16) & 0xFF;
 344         array[2] = (ntohl(ct->tuplehash[dir].tuple.src.ip) >> 8) & 0xFF;
 345         array[3] = ntohl(ct->tuplehash[dir].tuple.src.ip) & 0xFF;
 346
 347         for (i = 0; i < ARRAY_SIZE(search); i++) {
 348                 if (search[i].dir != dir) continue;
 349
 350                 found = find_pattern(fb_ptr, (*pskb)->len - dataoff,
 351                                      search[i].pattern,
 352                                      search[i].plen,
 353                                      search[i].skip,
 354                                      search[i].term,
 355                                      &matchoff, &matchlen,
 356                                      array,
 357                                      search[i].getnum);
 358                 if (found) break;
 359         }
 360         if (found == -1) {
 361                 /* We don't usually drop packets.  After all, this is
 362                    connection tracking, not packet filtering.
 363                    However, it is necessary for accurate tracking in
 364                    this case. */
 365                 if (net_ratelimit())
 366                         printk("conntrack_ftp: partial %s %u+%u\n",
 367                                search[i].pattern,
 368                                ntohl(th->seq), datalen);
 369                 ret = NF_DROP;
 370                 goto out;
 371         } else if (found == 0) { /* No match */
 372                 ret = NF_ACCEPT;
 373                 goto out_update_nl;
 374         }
 375
 376         DEBUGP("conntrack_ftp: match `%s' (%u bytes at %u)\n",
 377                fb_ptr + matchoff, matchlen, ntohl(th->seq) + matchoff);
 378
 379         /* Allocate expectation which will be inserted */
 380         exp = ip_conntrack_expect_alloc();
 381         if (exp == NULL) {
 382                 ret = NF_DROP;
 383                 goto out;
 384         }
 385
 386         /* We refer to the reverse direction ("!dir") tuples here,
 387          * because we're expecting something in the other direction.
 388          * Doesn't matter unless NAT is happening.  */
 389         exp->tuple.dst.ip = ct->tuplehash[!dir].tuple.dst.ip;
 390
 391         if (htonl((array[0] << 24) | (array[1] << 16) | (array[2] << 8) | array[3])
 392             != ct->tuplehash[dir].tuple.src.ip) {
 393                 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 394                    server: it really wants us to connect to a
 395                    different IP address.  Simply don't record it for
 396                    NAT. */
 397                 DEBUGP("conntrack_ftp: NOT RECORDING: %u,%u,%u,%u != %u.%u.%u.%u\n",
 398                        array[0], array[1], array[2], array[3],
 399                        NIPQUAD(ct->tuplehash[dir].tuple.src.ip));
 400
 401                 /* Thanks to Cristiano Lincoln Mattos
 402                    <lincoln@cesar.org.br> for reporting this potential
 403                    problem (DMZ machines opening holes to internal
 404                    networks, or the packet filter itself). */
 405                 if (!loose) {
 406                         ret = NF_ACCEPT;
 407                         ip_conntrack_expect_free(exp);
 408                         goto out_update_nl;
 409                 }
 410                 exp->tuple.dst.ip = htonl((array[0] << 24) | (array[1] << 16)
 411                                          | (array[2] << 8) | array[3]);
 412         }
 413
 414         exp->tuple.src.ip = ct->tuplehash[!dir].tuple.src.ip;
 415         exp->tuple.dst.u.tcp.port = htons(array[4] << 8 | array[5]);
 416         exp->tuple.src.u.tcp.port = 0; /* Don't care. */
 417         exp->tuple.dst.protonum = IPPROTO_TCP;
 418         exp->mask = ((struct ip_conntrack_tuple)
 419                 { { 0xFFFFFFFF, { 0 } },
 420                   { 0xFFFFFFFF, { .tcp = { 0xFFFF } }, 0xFF }});
 421
 422         exp->expectfn = NULL;
 423         exp->master = ct;
 424
 425         /* Now, NAT might want to mangle the packet, and register the
 426          * (possibly changed) expectation itself. */
 427         if (ip_nat_ftp_hook)
 428                 ret = ip_nat_ftp_hook(pskb, ctinfo, search[i].ftptype,
 429                                       matchoff, matchlen, exp, &seq);
 430         else {
 431                 /* Can't expect this?  Best to drop packet now. */
 432                 if (ip_conntrack_expect_related(exp) != 0) {
 433                         ip_conntrack_expect_free(exp);
 434                         ret = NF_DROP;
 435                 } else
 436                         ret = NF_ACCEPT;
 437         }
 438
 439 out_update_nl:
 440         /* Now if this ends in \n, update ftp info.  Seq may have been
 441          * adjusted by NAT code. */
 442         if (ends_in_nl)
 443                 update_nl_seq(seq, ct_ftp_info,dir);
 444  out:
 445         UNLOCK_BH(&ip_ftp_lock);
 446         return ret;
 447 }
 448
 449 static struct ip_conntrack_helper ftp[MAX_PORTS];
 450 static char ftp_names[MAX_PORTS][10];
 451
 452 /* Not __exit: called from init() */
 453 static void fini(void)
 454 {
 455         int i;
 456         for (i = 0; i < ports_c; i++) {
 457                 DEBUGP("ip_ct_ftp: unregistering helper for port %d\n",
 458                                 ports[i]);
 459                 ip_conntrack_helper_unregister(&ftp[i]);
 460         }
 461 }
 462
 463 static int __init init(void)
 464 {
 465         int i, ret;
 466         char *tmpname;
 467
 468         if (ports_c == 0)
 469                 ports[ports_c++] = FTP_PORT;
 470
 471         for (i = 0; i < ports_c; i++) {
 472                 ftp[i].tuple.src.u.tcp.port = htons(ports[i]);
 473                 ftp[i].tuple.dst.protonum = IPPROTO_TCP;
 474                 ftp[i].mask.src.u.tcp.port = 0xFFFF;
 475                 ftp[i].mask.dst.protonum = 0xFF;
 476                 ftp[i].max_expected = 1;
 477                 ftp[i].timeout = 5 * 60; /* 5 minutes */
 478                 ftp[i].me = THIS_MODULE;
 479                 ftp[i].help = help;
 480
 481                 tmpname = &ftp_names[i][0];
 482                 if (ports[i] == FTP_PORT)
 483                         sprintf(tmpname, "ftp");
 484                 else
 485                         sprintf(tmpname, "ftp-%d", ports[i]);
 486                 ftp[i].name = tmpname;
 487
 488                 DEBUGP("ip_ct_ftp: registering helper for port %d\n",
 489                                 ports[i]);
 490                 ret = ip_conntrack_helper_register(&ftp[i]);
 491
 492                 if (ret) {
 493                         fini();
 494                         return ret;
 495                 }
 496         }
 497         return 0;
 498 }
 499
 500 module_init(init);
 501 module_exit(fini);