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Linux/net/netfilter/ipvs/ip_vs_ftp.c

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  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 "
 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 int ports_count = 1;
 56 static unsigned short ports[IP_VS_APP_MAX_PORTS] = {21, 0};
 57 module_param_array(ports, ushort, &ports_count, 0444);
 58 MODULE_PARM_DESC(ports, "Ports to monitor for FTP control commands");
 59 
 60 
 61 /*      Dummy variable */
 62 static int ip_vs_ftp_pasv;
 63 
 64 
 65 static int
 66 ip_vs_ftp_init_conn(struct ip_vs_app *app, struct ip_vs_conn *cp)
 67 {
 68         /* We use connection tracking for the command connection */
 69         cp->flags |= IP_VS_CONN_F_NFCT;
 70         return 0;
 71 }
 72 
 73 
 74 static int
 75 ip_vs_ftp_done_conn(struct ip_vs_app *app, struct ip_vs_conn *cp)
 76 {
 77         return 0;
 78 }
 79 
 80 
 81 /*
 82  * Get <addr,port> from the string "xxx.xxx.xxx.xxx,ppp,ppp", started
 83  * with the "pattern", ignoring before "skip" and terminated with
 84  * the "term" character.
 85  * <addr,port> is in network order.
 86  */
 87 static int ip_vs_ftp_get_addrport(char *data, char *data_limit,
 88                                   const char *pattern, size_t plen,
 89                                   char skip, char term,
 90                                   __be32 *addr, __be16 *port,
 91                                   char **start, char **end)
 92 {
 93         char *s, c;
 94         unsigned char p[6];
 95         int i = 0;
 96 
 97         if (data_limit - data < plen) {
 98                 /* check if there is partial match */
 99                 if (strncasecmp(data, pattern, data_limit - data) == 0)
100                         return -1;
101                 else
102                         return 0;
103         }
104 
105         if (strncasecmp(data, pattern, plen) != 0) {
106                 return 0;
107         }
108         s = data + plen;
109         if (skip) {
110                 int found = 0;
111 
112                 for (;; s++) {
113                         if (s == data_limit)
114                                 return -1;
115                         if (!found) {
116                                 if (*s == skip)
117                                         found = 1;
118                         } else if (*s != skip) {
119                                 break;
120                         }
121                 }
122         }
123 
124         for (data = s; ; data++) {
125                 if (data == data_limit)
126                         return -1;
127                 if (*data == term)
128                         break;
129         }
130         *end = data;
131 
132         memset(p, 0, sizeof(p));
133         for (data = s; ; data++) {
134                 c = *data;
135                 if (c == term)
136                         break;
137                 if (c >= '' && c <= '9') {
138                         p[i] = p[i]*10 + c - '';
139                 } else if (c == ',' && i < 5) {
140                         i++;
141                 } else {
142                         /* unexpected character */
143                         return -1;
144                 }
145         }
146 
147         if (i != 5)
148                 return -1;
149 
150         *start = s;
151         *addr = get_unaligned((__be32 *) p);
152         *port = get_unaligned((__be16 *) (p + 4));
153         return 1;
154 }
155 
156 /*
157  * Look at outgoing ftp packets to catch the response to a PASV command
158  * from the server (inside-to-outside).
159  * When we see one, we build a connection entry with the client address,
160  * client port 0 (unknown at the moment), the server address and the
161  * server port.  Mark the current connection entry as a control channel
162  * of the new entry. All this work is just to make the data connection
163  * can be scheduled to the right server later.
164  *
165  * The outgoing packet should be something like
166  *   "227 Entering Passive Mode (xxx,xxx,xxx,xxx,ppp,ppp)".
167  * xxx,xxx,xxx,xxx is the server address, ppp,ppp is the server port number.
168  */
169 static int ip_vs_ftp_out(struct ip_vs_app *app, struct ip_vs_conn *cp,
170                          struct sk_buff *skb, int *diff)
171 {
172         struct iphdr *iph;
173         struct tcphdr *th;
174         char *data, *data_limit;
175         char *start, *end;
176         union nf_inet_addr from;
177         __be16 port;
178         struct ip_vs_conn *n_cp;
179         char buf[24];           /* xxx.xxx.xxx.xxx,ppp,ppp\000 */
180         unsigned int buf_len;
181         int ret = 0;
182         enum ip_conntrack_info ctinfo;
183         struct nf_conn *ct;
184 
185         *diff = 0;
186 
187 #ifdef CONFIG_IP_VS_IPV6
188         /* This application helper doesn't work with IPv6 yet,
189          * so turn this into a no-op for IPv6 packets
190          */
191         if (cp->af == AF_INET6)
192                 return 1;
193 #endif
194 
195         /* Only useful for established sessions */
196         if (cp->state != IP_VS_TCP_S_ESTABLISHED)
197                 return 1;
198 
199         /* Linear packets are much easier to deal with. */
200         if (!skb_make_writable(skb, skb->len))
201                 return 0;
202 
203         if (cp->app_data == &ip_vs_ftp_pasv) {
204                 iph = ip_hdr(skb);
205                 th = (struct tcphdr *)&(((char *)iph)[iph->ihl*4]);
206                 data = (char *)th + (th->doff << 2);
207                 data_limit = skb_tail_pointer(skb);
208 
209                 if (ip_vs_ftp_get_addrport(data, data_limit,
210                                            SERVER_STRING,
211                                            sizeof(SERVER_STRING)-1,
212                                            '(', ')',
213                                            &from.ip, &port,
214                                            &start, &end) != 1)
215                         return 1;
216 
217                 IP_VS_DBG(7, "PASV response (%pI4:%d) -> %pI4:%d detected\n",
218                           &from.ip, ntohs(port), &cp->caddr.ip, 0);
219 
220                 /*
221                  * Now update or create an connection entry for it
222                  */
223                 {
224                         struct ip_vs_conn_param p;
225                         ip_vs_conn_fill_param(cp->ipvs, AF_INET,
226                                               iph->protocol, &from, port,
227                                               &cp->caddr, 0, &p);
228                         n_cp = ip_vs_conn_out_get(&p);
229                 }
230                 if (!n_cp) {
231                         struct ip_vs_conn_param p;
232                         ip_vs_conn_fill_param(cp->ipvs,
233                                               AF_INET, IPPROTO_TCP, &cp->caddr,
234                                               0, &cp->vaddr, port, &p);
235                         /* As above, this is ipv4 only */
236                         n_cp = ip_vs_conn_new(&p, AF_INET, &from, port,
237                                               IP_VS_CONN_F_NO_CPORT |
238                                               IP_VS_CONN_F_NFCT,
239                                               cp->dest, skb->mark);
240                         if (!n_cp)
241                                 return 0;
242 
243                         /* add its controller */
244                         ip_vs_control_add(n_cp, cp);
245                 }
246 
247                 /*
248                  * Replace the old passive address with the new one
249                  */
250                 from.ip = n_cp->vaddr.ip;
251                 port = n_cp->vport;
252                 snprintf(buf, sizeof(buf), "%u,%u,%u,%u,%u,%u",
253                          ((unsigned char *)&from.ip)[0],
254                          ((unsigned char *)&from.ip)[1],
255                          ((unsigned char *)&from.ip)[2],
256                          ((unsigned char *)&from.ip)[3],
257                          ntohs(port) >> 8,
258                          ntohs(port) & 0xFF);
259 
260                 buf_len = strlen(buf);
261 
262                 ct = nf_ct_get(skb, &ctinfo);
263                 if (ct && !nf_ct_is_untracked(ct) && nfct_nat(ct)) {
264                         /* If mangling fails this function will return 0
265                          * which will cause the packet to be dropped.
266                          * Mangling can only fail under memory pressure,
267                          * hopefully it will succeed on the retransmitted
268                          * packet.
269                          */
270                         rcu_read_lock();
271                         ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
272                                                        iph->ihl * 4,
273                                                        start-data, end-start,
274                                                        buf, buf_len);
275                         rcu_read_unlock();
276                         if (ret) {
277                                 ip_vs_nfct_expect_related(skb, ct, n_cp,
278                                                           IPPROTO_TCP, 0, 0);
279                                 if (skb->ip_summed == CHECKSUM_COMPLETE)
280                                         skb->ip_summed = CHECKSUM_UNNECESSARY;
281                                 /* csum is updated */
282                                 ret = 1;
283                         }
284                 }
285 
286                 /*
287                  * Not setting 'diff' is intentional, otherwise the sequence
288                  * would be adjusted twice.
289                  */
290 
291                 cp->app_data = NULL;
292                 ip_vs_tcp_conn_listen(n_cp);
293                 ip_vs_conn_put(n_cp);
294                 return ret;
295         }
296         return 1;
297 }
298 
299 
300 /*
301  * Look at incoming ftp packets to catch the PASV/PORT command
302  * (outside-to-inside).
303  *
304  * The incoming packet having the PORT command should be something like
305  *      "PORT xxx,xxx,xxx,xxx,ppp,ppp\n".
306  * xxx,xxx,xxx,xxx is the client address, ppp,ppp is the client port number.
307  * In this case, we create a connection entry using the client address and
308  * port, so that the active ftp data connection from the server can reach
309  * the client.
310  */
311 static int ip_vs_ftp_in(struct ip_vs_app *app, struct ip_vs_conn *cp,
312                         struct sk_buff *skb, int *diff)
313 {
314         struct iphdr *iph;
315         struct tcphdr *th;
316         char *data, *data_start, *data_limit;
317         char *start, *end;
318         union nf_inet_addr to;
319         __be16 port;
320         struct ip_vs_conn *n_cp;
321 
322         /* no diff required for incoming packets */
323         *diff = 0;
324 
325 #ifdef CONFIG_IP_VS_IPV6
326         /* This application helper doesn't work with IPv6 yet,
327          * so turn this into a no-op for IPv6 packets
328          */
329         if (cp->af == AF_INET6)
330                 return 1;
331 #endif
332 
333         /* Only useful for established sessions */
334         if (cp->state != IP_VS_TCP_S_ESTABLISHED)
335                 return 1;
336 
337         /* Linear packets are much easier to deal with. */
338         if (!skb_make_writable(skb, skb->len))
339                 return 0;
340 
341         /*
342          * Detecting whether it is passive
343          */
344         iph = ip_hdr(skb);
345         th = (struct tcphdr *)&(((char *)iph)[iph->ihl*4]);
346 
347         /* Since there may be OPTIONS in the TCP packet and the HLEN is
348            the length of the header in 32-bit multiples, it is accurate
349            to calculate data address by th+HLEN*4 */
350         data = data_start = (char *)th + (th->doff << 2);
351         data_limit = skb_tail_pointer(skb);
352 
353         while (data <= data_limit - 6) {
354                 if (strncasecmp(data, "PASV\r\n", 6) == 0) {
355                         /* Passive mode on */
356                         IP_VS_DBG(7, "got PASV at %td of %td\n",
357                                   data - data_start,
358                                   data_limit - data_start);
359                         cp->app_data = &ip_vs_ftp_pasv;
360                         return 1;
361                 }
362                 data++;
363         }
364 
365         /*
366          * To support virtual FTP server, the scenerio is as follows:
367          *       FTP client ----> Load Balancer ----> FTP server
368          * First detect the port number in the application data,
369          * then create a new connection entry for the coming data
370          * connection.
371          */
372         if (ip_vs_ftp_get_addrport(data_start, data_limit,
373                                    CLIENT_STRING, sizeof(CLIENT_STRING)-1,
374                                    ' ', '\r', &to.ip, &port,
375                                    &start, &end) != 1)
376                 return 1;
377 
378         IP_VS_DBG(7, "PORT %pI4:%d detected\n", &to.ip, ntohs(port));
379 
380         /* Passive mode off */
381         cp->app_data = NULL;
382 
383         /*
384          * Now update or create a connection entry for it
385          */
386         IP_VS_DBG(7, "protocol %s %pI4:%d %pI4:%d\n",
387                   ip_vs_proto_name(iph->protocol),
388                   &to.ip, ntohs(port), &cp->vaddr.ip, 0);
389 
390         {
391                 struct ip_vs_conn_param p;
392                 ip_vs_conn_fill_param(cp->ipvs, AF_INET,
393                                       iph->protocol, &to, port, &cp->vaddr,
394                                       htons(ntohs(cp->vport)-1), &p);
395                 n_cp = ip_vs_conn_in_get(&p);
396                 if (!n_cp) {
397                         /* This is ipv4 only */
398                         n_cp = ip_vs_conn_new(&p, AF_INET, &cp->daddr,
399                                               htons(ntohs(cp->dport)-1),
400                                               IP_VS_CONN_F_NFCT, cp->dest,
401                                               skb->mark);
402                         if (!n_cp)
403                                 return 0;
404 
405                         /* add its controller */
406                         ip_vs_control_add(n_cp, cp);
407                 }
408         }
409 
410         /*
411          *      Move tunnel to listen state
412          */
413         ip_vs_tcp_conn_listen(n_cp);
414         ip_vs_conn_put(n_cp);
415 
416         return 1;
417 }
418 
419 
420 static struct ip_vs_app ip_vs_ftp = {
421         .name =         "ftp",
422         .type =         IP_VS_APP_TYPE_FTP,
423         .protocol =     IPPROTO_TCP,
424         .module =       THIS_MODULE,
425         .incs_list =    LIST_HEAD_INIT(ip_vs_ftp.incs_list),
426         .init_conn =    ip_vs_ftp_init_conn,
427         .done_conn =    ip_vs_ftp_done_conn,
428         .bind_conn =    NULL,
429         .unbind_conn =  NULL,
430         .pkt_out =      ip_vs_ftp_out,
431         .pkt_in =       ip_vs_ftp_in,
432 };
433 
434 /*
435  *      per netns ip_vs_ftp initialization
436  */
437 static int __net_init __ip_vs_ftp_init(struct net *net)
438 {
439         int i, ret;
440         struct ip_vs_app *app;
441         struct netns_ipvs *ipvs = net_ipvs(net);
442 
443         if (!ipvs)
444                 return -ENOENT;
445 
446         app = register_ip_vs_app(ipvs, &ip_vs_ftp);
447         if (IS_ERR(app))
448                 return PTR_ERR(app);
449 
450         for (i = 0; i < ports_count; i++) {
451                 if (!ports[i])
452                         continue;
453                 ret = register_ip_vs_app_inc(ipvs, app, app->protocol, ports[i]);
454                 if (ret)
455                         goto err_unreg;
456                 pr_info("%s: loaded support on port[%d] = %d\n",
457                         app->name, i, ports[i]);
458         }
459         return 0;
460 
461 err_unreg:
462         unregister_ip_vs_app(ipvs, &ip_vs_ftp);
463         return ret;
464 }
465 /*
466  *      netns exit
467  */
468 static void __ip_vs_ftp_exit(struct net *net)
469 {
470         struct netns_ipvs *ipvs = net_ipvs(net);
471 
472         if (!ipvs)
473                 return;
474 
475         unregister_ip_vs_app(ipvs, &ip_vs_ftp);
476 }
477 
478 static struct pernet_operations ip_vs_ftp_ops = {
479         .init = __ip_vs_ftp_init,
480         .exit = __ip_vs_ftp_exit,
481 };
482 
483 static int __init ip_vs_ftp_init(void)
484 {
485         int rv;
486 
487         rv = register_pernet_subsys(&ip_vs_ftp_ops);
488         /* rcu_barrier() is called by netns on error */
489         return rv;
490 }
491 
492 /*
493  *      ip_vs_ftp finish.
494  */
495 static void __exit ip_vs_ftp_exit(void)
496 {
497         unregister_pernet_subsys(&ip_vs_ftp_ops);
498         /* rcu_barrier() is called by netns */
499 }
500 
501 
502 module_init(ip_vs_ftp_init);
503 module_exit(ip_vs_ftp_exit);
504 MODULE_LICENSE("GPL");
505 

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