net/netfilter/ipvs/ip_vs_ftp.c

   1 /*
   2  * ip_vs_ftp.c: IPVS ftp application module
   3  *
   4  * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
   5  *
   6  * Changes:
   7  *
   8  *
   9  *      This program is free software; you can redistribute it and/or
  10  *      modify it under the terms of the GNU General Public License
  11  *      as published by the Free Software Foundation; either version
  12  *      2 of the License, or (at your option) any later version.
  13  *
  14  * Most code here is taken from ip_masq_ftp.c in kernel 2.2. The difference
  15  * is that ip_vs_ftp module handles the reverse direction to ip_masq_ftp.
  16  *
  17  *              IP_MASQ_FTP ftp masquerading module
  18  *
  19  * Version:     @(#)ip_masq_ftp.c 0.04   02/05/96
  20  *
  21  * Author:      Wouter Gadeyne
  22  *
  23  */
  24
  25 #define KMSG_COMPONENT "IPVS"
  26 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
  27
  28 #include <linux/module.h>
  29 #include <linux/moduleparam.h>
  30 #include <linux/kernel.h>
  31 #include <linux/skbuff.h>
  32 #include <linux/in.h>
  33 #include <linux/ip.h>
  34 #include <linux/netfilter.h>
  35 #include <net/netfilter/nf_conntrack.h>
  36 #include <net/netfilter/nf_conntrack_expect.h>
  37 #include <net/netfilter/nf_nat.h>
  38 #include <net/netfilter/nf_nat_helper.h>
  39 #include <linux/gfp.h>
  40 #include <net/protocol.h>
  41 #include <net/tcp.h>
  42 #include <asm/unaligned.h>
  43
  44 #include <net/ip_vs.h>
  45
  46
  47 #define SERVER_STRING "227 Entering Passive Mode ("
  48 #define CLIENT_STRING "PORT "
  49
  50
  51 /*
  52  * List of ports (up to IP_VS_APP_MAX_PORTS) to be handled by helper
  53  * First port is set to the default port.
  54  */
  55 static unsigned short ports[IP_VS_APP_MAX_PORTS] = {21, 0};
  56 module_param_array(ports, ushort, NULL, 0);
  57 MODULE_PARM_DESC(ports, "Ports to monitor for FTP control commands");
  58
  59
  60 /*      Dummy variable */
  61 static int ip_vs_ftp_pasv;
  62
  63
  64 static int
  65 ip_vs_ftp_init_conn(struct ip_vs_app *app, struct ip_vs_conn *cp)
  66 {
  67         /* We use connection tracking for the command connection */
  68         cp->flags |= IP_VS_CONN_F_NFCT;
  69         return 0;
  70 }
  71
  72
  73 static int
  74 ip_vs_ftp_done_conn(struct ip_vs_app *app, struct ip_vs_conn *cp)
  75 {
  76         return 0;
  77 }
  78
  79
  80 /*
  81  * Get <addr,port> from the string "xxx.xxx.xxx.xxx,ppp,ppp", started
  82  * with the "pattern" and terminated with the "term" character.
  83  * <addr,port> is in network order.
  84  */
  85 static int ip_vs_ftp_get_addrport(char *data, char *data_limit,
  86                                   const char *pattern, size_t plen, char term,
  87                                   __be32 *addr, __be16 *port,
  88                                   char **start, char **end)
  89 {
  90         unsigned char p[6];
  91         int i = 0;
  92
  93         if (data_limit - data < plen) {
  94                 /* check if there is partial match */
  95                 if (strnicmp(data, pattern, data_limit - data) == 0)
  96                         return -1;
  97                 else
  98                         return 0;
  99         }
 100
 101         if (strnicmp(data, pattern, plen) != 0) {
 102                 return 0;
 103         }
 104         *start = data + plen;
 105
 106         for (data = *start; *data != term; data++) {
 107                 if (data == data_limit)
 108                         return -1;
 109         }
 110         *end = data;
 111
 112         memset(p, 0, sizeof(p));
 113         for (data = *start; data != *end; data++) {
 114                 if (*data >= '0' && *data <= '9') {
 115                         p[i] = p[i]*10 + *data - '0';
 116                 } else if (*data == ',' && i < 5) {
 117                         i++;
 118                 } else {
 119                         /* unexpected character */
 120                         return -1;
 121                 }
 122         }
 123
 124         if (i != 5)
 125                 return -1;
 126
 127         *addr = get_unaligned((__be32 *)p);
 128         *port = get_unaligned((__be16 *)(p + 4));
 129         return 1;
 130 }
 131
 132 /*
 133  * Look at outgoing ftp packets to catch the response to a PASV command
 134  * from the server (inside-to-outside).
 135  * When we see one, we build a connection entry with the client address,
 136  * client port 0 (unknown at the moment), the server address and the
 137  * server port.  Mark the current connection entry as a control channel
 138  * of the new entry. All this work is just to make the data connection
 139  * can be scheduled to the right server later.
 140  *
 141  * The outgoing packet should be something like
 142  *   "227 Entering Passive Mode (xxx,xxx,xxx,xxx,ppp,ppp)".
 143  * xxx,xxx,xxx,xxx is the server address, ppp,ppp is the server port number.
 144  */
 145 static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
 146                          struct sk_buff *skb, int *diff)
 147 {
 148         struct iphdr *iph;
 149         struct tcphdr *th;
 150         char *data, *data_limit;
 151         char *start, *end;
 152         union nf_inet_addr from;
 153         __be16 port;
 154         struct ip_vs_conn *n_cp;
 155         char buf[24];           /* xxx.xxx.xxx.xxx,ppp,ppp\000 */
 156         unsigned buf_len;
 157         int ret = 0;
 158         enum ip_conntrack_info ctinfo;
 159         struct nf_conn *ct;
 160
 161 #ifdef CONFIG_IP_VS_IPV6
 162         /* This application helper doesn't work with IPv6 yet,
 163          * so turn this into a no-op for IPv6 packets
 164          */
 165         if (cp->af == AF_INET6)
 166                 return 1;
 167 #endif
 168
 169         *diff = 0;
 170
 171         /* Only useful for established sessions */
 172         if (cp->state != IP_VS_TCP_S_ESTABLISHED)
 173                 return 1;
 174
 175         /* Linear packets are much easier to deal with. */
 176         if (!skb_make_writable(skb, skb->len))
 177                 return 0;
 178
 179         if (cp->app_data == &ip_vs_ftp_pasv) {
 180                 iph = ip_hdr(skb);
 181                 th = (struct tcphdr *)&(((char *)iph)[iph->ihl*4]);
 182                 data = (char *)th + (th->doff << 2);
 183                 data_limit = skb_tail_pointer(skb);
 184
 185                 if (ip_vs_ftp_get_addrport(data, data_limit,
 186                                            SERVER_STRING,
 187                                            sizeof(SERVER_STRING)-1, ')',
 188                                            &from.ip, &port,
 189                                            &start, &end) != 1)
 190                         return 1;
 191
 192                 IP_VS_DBG(7, "PASV response (%pI4:%d) -> %pI4:%d detected\n",
 193                           &from.ip, ntohs(port), &cp->caddr.ip, 0);
 194
 195                 /*
 196                  * Now update or create an connection entry for it
 197                  */
 198                 {
 199                         struct ip_vs_conn_param p;
 200                         ip_vs_conn_fill_param(AF_INET, iph->protocol,
 201                                               &from, port, &cp->caddr, 0, &p);
 202                         n_cp = ip_vs_conn_out_get(&p);
 203                 }
 204                 if (!n_cp) {
 205                         struct ip_vs_conn_param p;
 206                         ip_vs_conn_fill_param(AF_INET, IPPROTO_TCP, &cp->caddr,
 207                                               0, &cp->vaddr, port, &p);
 208                         n_cp = ip_vs_conn_new(&p, &from, port,
 209                                               IP_VS_CONN_F_NO_CPORT |
 210                                               IP_VS_CONN_F_NFCT,
 211                                               cp->dest);
 212                         if (!n_cp)
 213                                 return 0;
 214
 215                         /* add its controller */
 216                         ip_vs_control_add(n_cp, cp);
 217                 }
 218
 219                 /*
 220                  * Replace the old passive address with the new one
 221                  */
 222                 from.ip = n_cp->vaddr.ip;
 223                 port = n_cp->vport;
 224                 snprintf(buf, sizeof(buf), "%u,%u,%u,%u,%u,%u",
 225                          ((unsigned char *)&from.ip)[0],
 226                          ((unsigned char *)&from.ip)[1],
 227                          ((unsigned char *)&from.ip)[2],
 228                          ((unsigned char *)&from.ip)[3],
 229                          ntohs(port) >> 8,
 230                          ntohs(port) & 0xFF);
 231
 232                 buf_len = strlen(buf);
 233
 234                 ct = nf_ct_get(skb, &ctinfo);
 235                 if (ct && !nf_ct_is_untracked(ct) && nfct_nat(ct)) {
 236                         /* If mangling fails this function will return 0
 237                          * which will cause the packet to be dropped.
 238                          * Mangling can only fail under memory pressure,
 239                          * hopefully it will succeed on the retransmitted
 240                          * packet.
 241                          */
 242                         ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
 243                                                        start-data, end-start,
 244                                                        buf, buf_len);
 245                         if (ret) {
 246                                 ip_vs_nfct_expect_related(skb, ct, n_cp,
 247                                                           IPPROTO_TCP, 0, 0);
 248                                 if (skb->ip_summed == CHECKSUM_COMPLETE)
 249                                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 250                                 /* csum is updated */
 251                                 ret = 1;
 252                         }
 253                 }
 254
 255                 /*
 256                  * Not setting 'diff' is intentional, otherwise the sequence
 257                  * would be adjusted twice.
 258                  */
 259
 260                 cp->app_data = NULL;
 261                 ip_vs_tcp_conn_listen(n_cp);
 262                 ip_vs_conn_put(n_cp);
 263                 return ret;
 264         }
 265         return 1;
 266 }
 267
 268
 269 /*
 270  * Look at incoming ftp packets to catch the PASV/PORT command
 271  * (outside-to-inside).
 272  *
 273  * The incoming packet having the PORT command should be something like
 274  *      "PORT xxx,xxx,xxx,xxx,ppp,ppp\n".
 275  * xxx,xxx,xxx,xxx is the client address, ppp,ppp is the client port number.
 276  * In this case, we create a connection entry using the client address and
 277  * port, so that the active ftp data connection from the server can reach
 278  * the client.
 279  */
 280 static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
 281                         struct sk_buff *skb, int *diff)
 282 {
 283         struct iphdr *iph;
 284         struct tcphdr *th;
 285         char *data, *data_start, *data_limit;
 286         char *start, *end;
 287         union nf_inet_addr to;
 288         __be16 port;
 289         struct ip_vs_conn *n_cp;
 290
 291 #ifdef CONFIG_IP_VS_IPV6
 292         /* This application helper doesn't work with IPv6 yet,
 293          * so turn this into a no-op for IPv6 packets
 294          */
 295         if (cp->af == AF_INET6)
 296                 return 1;
 297 #endif
 298
 299         /* no diff required for incoming packets */
 300         *diff = 0;
 301
 302         /* Only useful for established sessions */
 303         if (cp->state != IP_VS_TCP_S_ESTABLISHED)
 304                 return 1;
 305
 306         /* Linear packets are much easier to deal with. */
 307         if (!skb_make_writable(skb, skb->len))
 308                 return 0;
 309
 310         /*
 311          * Detecting whether it is passive
 312          */
 313         iph = ip_hdr(skb);
 314         th = (struct tcphdr *)&(((char *)iph)[iph->ihl*4]);
 315
 316         /* Since there may be OPTIONS in the TCP packet and the HLEN is
 317            the length of the header in 32-bit multiples, it is accurate
 318            to calculate data address by th+HLEN*4 */
 319         data = data_start = (char *)th + (th->doff << 2);
 320         data_limit = skb_tail_pointer(skb);
 321
 322         while (data <= data_limit - 6) {
 323                 if (strnicmp(data, "PASV\r\n", 6) == 0) {
 324                         /* Passive mode on */
 325                         IP_VS_DBG(7, "got PASV at %td of %td\n",
 326                                   data - data_start,
 327                                   data_limit - data_start);
 328                         cp->app_data = &ip_vs_ftp_pasv;
 329                         return 1;
 330                 }
 331                 data++;
 332         }
 333
 334         /*
 335          * To support virtual FTP server, the scenerio is as follows:
 336          *       FTP client ----> Load Balancer ----> FTP server
 337          * First detect the port number in the application data,
 338          * then create a new connection entry for the coming data
 339          * connection.
 340          */
 341         if (ip_vs_ftp_get_addrport(data_start, data_limit,
 342                                    CLIENT_STRING, sizeof(CLIENT_STRING)-1,
 343                                    '\r', &to.ip, &port,
 344                                    &start, &end) != 1)
 345                 return 1;
 346
 347         IP_VS_DBG(7, "PORT %pI4:%d detected\n", &to.ip, ntohs(port));
 348
 349         /* Passive mode off */
 350         cp->app_data = NULL;
 351
 352         /*
 353          * Now update or create a connection entry for it
 354          */
 355         IP_VS_DBG(7, "protocol %s %pI4:%d %pI4:%d\n",
 356                   ip_vs_proto_name(iph->protocol),
 357                   &to.ip, ntohs(port), &cp->vaddr.ip, 0);
 358
 359         {
 360                 struct ip_vs_conn_param p;
 361                 ip_vs_conn_fill_param(AF_INET, iph->protocol, &to, port,
 362                                       &cp->vaddr, htons(ntohs(cp->vport)-1),
 363                                       &p);
 364                 n_cp = ip_vs_conn_in_get(&p);
 365                 if (!n_cp) {
 366                         n_cp = ip_vs_conn_new(&p, &cp->daddr,
 367                                               htons(ntohs(cp->dport)-1),
 368                                               IP_VS_CONN_F_NFCT, cp->dest);
 369                         if (!n_cp)
 370                                 return 0;
 371
 372                         /* add its controller */
 373                         ip_vs_control_add(n_cp, cp);
 374                 }
 375         }
 376
 377         /*
 378          *      Move tunnel to listen state
 379          */
 380         ip_vs_tcp_conn_listen(n_cp);
 381         ip_vs_conn_put(n_cp);
 382
 383         return 1;
 384 }
 385
 386
 387 static struct ip_vs_app ip_vs_ftp = {
 388         .name =         "ftp",
 389         .type =         IP_VS_APP_TYPE_FTP,
 390         .protocol =     IPPROTO_TCP,
 391         .module =       THIS_MODULE,
 392         .incs_list =    LIST_HEAD_INIT(ip_vs_ftp.incs_list),
 393         .init_conn =    ip_vs_ftp_init_conn,
 394         .done_conn =    ip_vs_ftp_done_conn,
 395         .bind_conn =    NULL,
 396         .unbind_conn =  NULL,
 397         .pkt_out =      ip_vs_ftp_out,
 398         .pkt_in =       ip_vs_ftp_in,
 399 };
 400
 401
 402 /*
 403  *      ip_vs_ftp initialization
 404  */
 405 static int __init ip_vs_ftp_init(void)
 406 {
 407         int i, ret;
 408         struct ip_vs_app *app = &ip_vs_ftp;
 409
 410         ret = register_ip_vs_app(app);
 411         if (ret)
 412                 return ret;
 413
 414         for (i=0; i<IP_VS_APP_MAX_PORTS; i++) {
 415                 if (!ports[i])
 416                         continue;
 417                 ret = register_ip_vs_app_inc(app, app->protocol, ports[i]);
 418                 if (ret)
 419                         break;
 420                 pr_info("%s: loaded support on port[%d] = %d\n",
 421                         app->name, i, ports[i]);
 422         }
 423
 424         if (ret)
 425                 unregister_ip_vs_app(app);
 426
 427         return ret;
 428 }
 429
 430
 431 /*
 432  *      ip_vs_ftp finish.
 433  */
 434 static void __exit ip_vs_ftp_exit(void)
 435 {
 436         unregister_ip_vs_app(&ip_vs_ftp);
 437 }
 438
 439
 440 module_init(ip_vs_ftp_init);
 441 module_exit(ip_vs_ftp_exit);
 442 MODULE_LICENSE("GPL");