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