net/ipv4/netfilter/ip_conntrack_sip.c

   1 /* SIP extension for IP connection tracking.
   2  *
   3  * (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
   4  * based on RR's ip_conntrack_ftp.c and other modules.
   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/module.h>
  12 #include <linux/ctype.h>
  13 #include <linux/skbuff.h>
  14 #include <linux/in.h>
  15 #include <linux/ip.h>
  16 #include <linux/udp.h>
  17
  18 #include <linux/netfilter.h>
  19 #include <linux/netfilter_ipv4.h>
  20 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  21 #include <linux/netfilter_ipv4/ip_conntrack_sip.h>
  22
  23 #if 0
  24 #define DEBUGP printk
  25 #else
  26 #define DEBUGP(format, args...)
  27 #endif
  28
  29 MODULE_LICENSE("GPL");
  30 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  31 MODULE_DESCRIPTION("SIP connection tracking helper");
  32
  33 #define MAX_PORTS       8
  34 static unsigned short ports[MAX_PORTS];
  35 static int ports_c;
  36 module_param_array(ports, ushort, &ports_c, 0400);
  37 MODULE_PARM_DESC(ports, "port numbers of sip servers");
  38
  39 static unsigned int sip_timeout = SIP_TIMEOUT;
  40 module_param(sip_timeout, uint, 0600);
  41 MODULE_PARM_DESC(sip_timeout, "timeout for the master SIP session");
  42
  43 unsigned int (*ip_nat_sip_hook)(struct sk_buff **pskb,
  44                                 enum ip_conntrack_info ctinfo,
  45                                 struct ip_conntrack *ct,
  46                                 const char **dptr);
  47 EXPORT_SYMBOL_GPL(ip_nat_sip_hook);
  48
  49 unsigned int (*ip_nat_sdp_hook)(struct sk_buff **pskb,
  50                                 enum ip_conntrack_info ctinfo,
  51                                 struct ip_conntrack_expect *exp,
  52                                 const char *dptr);
  53 EXPORT_SYMBOL_GPL(ip_nat_sdp_hook);
  54
  55 static int digits_len(const char *dptr, const char *limit, int *shift);
  56 static int epaddr_len(const char *dptr, const char *limit, int *shift);
  57 static int skp_digits_len(const char *dptr, const char *limit, int *shift);
  58 static int skp_epaddr_len(const char *dptr, const char *limit, int *shift);
  59
  60 struct sip_header_nfo {
  61         const char      *lname;
  62         const char      *sname;
  63         const char      *ln_str;
  64         size_t          lnlen;
  65         size_t          snlen;
  66         size_t          ln_strlen;
  67         int             case_sensitive;
  68         int             (*match_len)(const char *, const char *, int *);
  69 };
  70
  71 static struct sip_header_nfo ct_sip_hdrs[] = {
  72         [POS_REG_REQ_URI] = {   /* SIP REGISTER request URI */
  73                 .lname          = "sip:",
  74                 .lnlen          = sizeof("sip:") - 1,
  75                 .ln_str         = ":",
  76                 .ln_strlen      = sizeof(":") - 1,
  77                 .match_len      = epaddr_len
  78         },
  79         [POS_REQ_URI] = {       /* SIP request URI */
  80                 .lname          = "sip:",
  81                 .lnlen          = sizeof("sip:") - 1,
  82                 .ln_str         = "@",
  83                 .ln_strlen      = sizeof("@") - 1,
  84                 .match_len      = epaddr_len
  85         },
  86         [POS_FROM] = {          /* SIP From header */
  87                 .lname          = "From:",
  88                 .lnlen          = sizeof("From:") - 1,
  89                 .sname          = "\r\nf:",
  90                 .snlen          = sizeof("\r\nf:") - 1,
  91                 .ln_str         = "sip:",
  92                 .ln_strlen      = sizeof("sip:") - 1,
  93                 .match_len      = skp_epaddr_len,
  94         },
  95         [POS_TO] = {            /* SIP To header */
  96                 .lname          = "To:",
  97                 .lnlen          = sizeof("To:") - 1,
  98                 .sname          = "\r\nt:",
  99                 .snlen          = sizeof("\r\nt:") - 1,
 100                 .ln_str         = "sip:",
 101                 .ln_strlen      = sizeof("sip:") - 1,
 102                 .match_len      = skp_epaddr_len,
 103         },
 104         [POS_VIA] = {           /* SIP Via header */
 105                 .lname          = "Via:",
 106                 .lnlen          = sizeof("Via:") - 1,
 107                 .sname          = "\r\nv:",
 108                 .snlen          = sizeof("\r\nv:") - 1, /* rfc3261 "\r\n" */
 109                 .ln_str         = "UDP ",
 110                 .ln_strlen      = sizeof("UDP ") - 1,
 111                 .match_len      = epaddr_len,
 112         },
 113         [POS_CONTACT] = {       /* SIP Contact header */
 114                 .lname          = "Contact:",
 115                 .lnlen          = sizeof("Contact:") - 1,
 116                 .sname          = "\r\nm:",
 117                 .snlen          = sizeof("\r\nm:") - 1,
 118                 .ln_str         = "sip:",
 119                 .ln_strlen      = sizeof("sip:") - 1,
 120                 .match_len      = skp_epaddr_len
 121         },
 122         [POS_CONTENT] = {       /* SIP Content length header */
 123                 .lname          = "Content-Length:",
 124                 .lnlen          = sizeof("Content-Length:") - 1,
 125                 .sname          = "\r\nl:",
 126                 .snlen          = sizeof("\r\nl:") - 1,
 127                 .ln_str         = ":",
 128                 .ln_strlen      = sizeof(":") - 1,
 129                 .match_len      = skp_digits_len
 130         },
 131         [POS_MEDIA] = {         /* SDP media info */
 132                 .case_sensitive = 1,
 133                 .lname          = "\nm=",
 134                 .lnlen          = sizeof("\nm=") - 1,
 135                 .sname          = "\rm=",
 136                 .snlen          = sizeof("\rm=") - 1,
 137                 .ln_str         = "audio ",
 138                 .ln_strlen      = sizeof("audio ") - 1,
 139                 .match_len      = digits_len
 140         },
 141         [POS_OWNER] = {         /* SDP owner address*/
 142                 .case_sensitive = 1,
 143                 .lname          = "\no=",
 144                 .lnlen          = sizeof("\no=") - 1,
 145                 .sname          = "\ro=",
 146                 .snlen          = sizeof("\ro=") - 1,
 147                 .ln_str         = "IN IP4 ",
 148                 .ln_strlen      = sizeof("IN IP4 ") - 1,
 149                 .match_len      = epaddr_len
 150         },
 151         [POS_CONNECTION] = {    /* SDP connection info */
 152                 .case_sensitive = 1,
 153                 .lname          = "\nc=",
 154                 .lnlen          = sizeof("\nc=") - 1,
 155                 .sname          = "\rc=",
 156                 .snlen          = sizeof("\rc=") - 1,
 157                 .ln_str         = "IN IP4 ",
 158                 .ln_strlen      = sizeof("IN IP4 ") - 1,
 159                 .match_len      = epaddr_len
 160         },
 161         [POS_SDP_HEADER] = {    /* SDP version header */
 162                 .case_sensitive = 1,
 163                 .lname          = "\nv=",
 164                 .lnlen          = sizeof("\nv=") - 1,
 165                 .sname          = "\rv=",
 166                 .snlen          = sizeof("\rv=") - 1,
 167                 .ln_str         = "=",
 168                 .ln_strlen      = sizeof("=") - 1,
 169                 .match_len      = digits_len
 170         }
 171 };
 172
 173 /* get line lenght until first CR or LF seen. */
 174 int ct_sip_lnlen(const char *line, const char *limit)
 175 {
 176         const char *k = line;
 177
 178         while ((line <= limit) && (*line == '\r' || *line == '\n'))
 179                 line++;
 180
 181         while (line <= limit) {
 182                 if (*line == '\r' || *line == '\n')
 183                         break;
 184                 line++;
 185         }
 186         return line - k;
 187 }
 188 EXPORT_SYMBOL_GPL(ct_sip_lnlen);
 189
 190 /* Linear string search, case sensitive. */
 191 const char *ct_sip_search(const char *needle, const char *haystack,
 192                           size_t needle_len, size_t haystack_len,
 193                           int case_sensitive)
 194 {
 195         const char *limit = haystack + (haystack_len - needle_len);
 196
 197         while (haystack <= limit) {
 198                 if (case_sensitive) {
 199                         if (strncmp(haystack, needle, needle_len) == 0)
 200                                 return haystack;
 201                 } else {
 202                         if (strnicmp(haystack, needle, needle_len) == 0)
 203                                 return haystack;
 204                 }
 205                 haystack++;
 206         }
 207         return NULL;
 208 }
 209 EXPORT_SYMBOL_GPL(ct_sip_search);
 210
 211 static int digits_len(const char *dptr, const char *limit, int *shift)
 212 {
 213         int len = 0;
 214         while (dptr <= limit && isdigit(*dptr)) {
 215                 dptr++;
 216                 len++;
 217         }
 218         return len;
 219 }
 220
 221 /* get digits lenght, skiping blank spaces. */
 222 static int skp_digits_len(const char *dptr, const char *limit, int *shift)
 223 {
 224         for (; dptr <= limit && *dptr == ' '; dptr++)
 225                 (*shift)++;
 226
 227         return digits_len(dptr, limit, shift);
 228 }
 229
 230 /* Simple ipaddr parser.. */
 231 static int parse_ipaddr(const char *cp, const char **endp,
 232                         __be32 *ipaddr, const char *limit)
 233 {
 234         unsigned long int val;
 235         int i, digit = 0;
 236
 237         for (i = 0, *ipaddr = 0; cp <= limit && i < 4; i++) {
 238                 digit = 0;
 239                 if (!isdigit(*cp))
 240                         break;
 241
 242                 val = simple_strtoul(cp, (char **)&cp, 10);
 243                 if (val > 0xFF)
 244                         return -1;
 245
 246                 ((u_int8_t *)ipaddr)[i] = val;
 247                 digit = 1;
 248
 249                 if (*cp != '.')
 250                         break;
 251                 cp++;
 252         }
 253         if (!digit)
 254                 return -1;
 255
 256         if (endp)
 257                 *endp = cp;
 258
 259         return 0;
 260 }
 261
 262 /* skip ip address. returns it lenght. */
 263 static int epaddr_len(const char *dptr, const char *limit, int *shift)
 264 {
 265         const char *aux = dptr;
 266         __be32 ip;
 267
 268         if (parse_ipaddr(dptr, &dptr, &ip, limit) < 0) {
 269                 DEBUGP("ip: %s parse failed.!\n", dptr);
 270                 return 0;
 271         }
 272
 273         /* Port number */
 274         if (*dptr == ':') {
 275                 dptr++;
 276                 dptr += digits_len(dptr, limit, shift);
 277         }
 278         return dptr - aux;
 279 }
 280
 281 /* get address length, skiping user info. */
 282 static int skp_epaddr_len(const char *dptr, const char *limit, int *shift)
 283 {
 284         int s = *shift;
 285
 286         /* Search for @, but stop at the end of the line.
 287          * We are inside a sip: URI, so we don't need to worry about
 288          * continuation lines. */
 289         while (dptr <= limit &&
 290                *dptr != '@' && *dptr != '\r' && *dptr != '\n') {
 291                 (*shift)++;
 292                 dptr++;
 293         }
 294
 295         if (dptr <= limit && *dptr == '@') {
 296                 dptr++;
 297                 (*shift)++;
 298         } else
 299                 *shift = s;
 300
 301         return epaddr_len(dptr, limit, shift);
 302 }
 303
 304 /* Returns 0 if not found, -1 error parsing. */
 305 int ct_sip_get_info(const char *dptr, size_t dlen,
 306                     unsigned int *matchoff,
 307                     unsigned int *matchlen,
 308                     enum sip_header_pos pos)
 309 {
 310         struct sip_header_nfo *hnfo = &ct_sip_hdrs[pos];
 311         const char *limit, *aux, *k = dptr;
 312         int shift = 0;
 313
 314         limit = dptr + (dlen - hnfo->lnlen);
 315
 316         while (dptr <= limit) {
 317                 if ((strncmp(dptr, hnfo->lname, hnfo->lnlen) != 0) &&
 318                     (hnfo->sname == NULL ||
 319                      strncmp(dptr, hnfo->sname, hnfo->snlen) != 0)) {
 320                         dptr++;
 321                         continue;
 322                 }
 323                 aux = ct_sip_search(hnfo->ln_str, dptr, hnfo->ln_strlen,
 324                                     ct_sip_lnlen(dptr, limit),
 325                                     hnfo->case_sensitive);
 326                 if (!aux) {
 327                         DEBUGP("'%s' not found in '%s'.\n", hnfo->ln_str,
 328                                hnfo->lname);
 329                         return -1;
 330                 }
 331                 aux += hnfo->ln_strlen;
 332
 333                 *matchlen = hnfo->match_len(aux, limit, &shift);
 334                 if (!*matchlen)
 335                         return -1;
 336
 337                 *matchoff = (aux - k) + shift;
 338
 339                 DEBUGP("%s match succeeded! - len: %u\n", hnfo->lname,
 340                        *matchlen);
 341                 return 1;
 342         }
 343         DEBUGP("%s header not found.\n", hnfo->lname);
 344         return 0;
 345 }
 346 EXPORT_SYMBOL_GPL(ct_sip_get_info);
 347
 348 static int set_expected_rtp(struct sk_buff **pskb,
 349                             struct ip_conntrack *ct,
 350                             enum ip_conntrack_info ctinfo,
 351                             __be32 ipaddr, u_int16_t port,
 352                             const char *dptr)
 353 {
 354         struct ip_conntrack_expect *exp;
 355         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 356         int ret;
 357         typeof(ip_nat_sdp_hook) ip_nat_sdp;
 358
 359         exp = ip_conntrack_expect_alloc(ct);
 360         if (exp == NULL)
 361                 return NF_DROP;
 362
 363         exp->tuple.src.ip = ct->tuplehash[!dir].tuple.src.ip;
 364         exp->tuple.src.u.udp.port = 0;
 365         exp->tuple.dst.ip = ipaddr;
 366         exp->tuple.dst.u.udp.port = htons(port);
 367         exp->tuple.dst.protonum = IPPROTO_UDP;
 368
 369         exp->mask.src.ip = htonl(0xFFFFFFFF);
 370         exp->mask.src.u.udp.port = 0;
 371         exp->mask.dst.ip = htonl(0xFFFFFFFF);
 372         exp->mask.dst.u.udp.port = htons(0xFFFF);
 373         exp->mask.dst.protonum = 0xFF;
 374
 375         exp->expectfn = NULL;
 376         exp->flags = 0;
 377
 378         ip_nat_sdp = rcu_dereference(ip_nat_sdp_hook);
 379         if (ip_nat_sdp)
 380                 ret = ip_nat_sdp(pskb, ctinfo, exp, dptr);
 381         else {
 382                 if (ip_conntrack_expect_related(exp) != 0)
 383                         ret = NF_DROP;
 384                 else
 385                         ret = NF_ACCEPT;
 386         }
 387         ip_conntrack_expect_put(exp);
 388
 389         return ret;
 390 }
 391
 392 static int sip_help(struct sk_buff **pskb,
 393                     struct ip_conntrack *ct,
 394                     enum ip_conntrack_info ctinfo)
 395 {
 396         unsigned int dataoff, datalen;
 397         const char *dptr;
 398         int ret = NF_ACCEPT;
 399         int matchoff, matchlen;
 400         __be32 ipaddr;
 401         u_int16_t port;
 402         typeof(ip_nat_sip_hook) ip_nat_sip;
 403
 404         /* No Data ? */
 405         dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
 406         if (dataoff >= (*pskb)->len) {
 407                 DEBUGP("skb->len = %u\n", (*pskb)->len);
 408                 return NF_ACCEPT;
 409         }
 410
 411         ip_ct_refresh(ct, *pskb, sip_timeout * HZ);
 412
 413         if (!skb_is_nonlinear(*pskb))
 414                 dptr = (*pskb)->data + dataoff;
 415         else {
 416                 DEBUGP("Copy of skbuff not supported yet.\n");
 417                 goto out;
 418         }
 419
 420         ip_nat_sip = rcu_dereference(ip_nat_sip_hook);
 421         if (ip_nat_sip) {
 422                 if (!ip_nat_sip(pskb, ctinfo, ct, &dptr)) {
 423                         ret = NF_DROP;
 424                         goto out;
 425                 }
 426         }
 427
 428         /* After this point NAT, could have mangled skb, so
 429            we need to recalculate payload lenght. */
 430         datalen = (*pskb)->len - dataoff;
 431
 432         if (datalen < (sizeof("SIP/2.0 200") - 1))
 433                 goto out;
 434
 435         /* RTP info only in some SDP pkts */
 436         if (memcmp(dptr, "INVITE", sizeof("INVITE") - 1) != 0 &&
 437             memcmp(dptr, "SIP/2.0 200", sizeof("SIP/2.0 200") - 1) != 0) {
 438                 goto out;
 439         }
 440         /* Get ip and port address from SDP packet. */
 441         if (ct_sip_get_info(dptr, datalen, &matchoff, &matchlen,
 442                             POS_CONNECTION) > 0) {
 443
 444                 /* We'll drop only if there are parse problems. */
 445                 if (parse_ipaddr(dptr + matchoff, NULL, &ipaddr,
 446                                  dptr + datalen) < 0) {
 447                         ret = NF_DROP;
 448                         goto out;
 449                 }
 450                 if (ct_sip_get_info(dptr, datalen, &matchoff, &matchlen,
 451                                     POS_MEDIA) > 0) {
 452
 453                         port = simple_strtoul(dptr + matchoff, NULL, 10);
 454                         if (port < 1024) {
 455                                 ret = NF_DROP;
 456                                 goto out;
 457                         }
 458                         ret = set_expected_rtp(pskb, ct, ctinfo,
 459                                                ipaddr, port, dptr);
 460                 }
 461         }
 462 out:
 463         return ret;
 464 }
 465
 466 static struct ip_conntrack_helper sip[MAX_PORTS];
 467 static char sip_names[MAX_PORTS][10];
 468
 469 static void fini(void)
 470 {
 471         int i;
 472         for (i = 0; i < ports_c; i++) {
 473                 DEBUGP("unregistering helper for port %d\n", ports[i]);
 474                 ip_conntrack_helper_unregister(&sip[i]);
 475         }
 476 }
 477
 478 static int __init init(void)
 479 {
 480         int i, ret;
 481         char *tmpname;
 482
 483         if (ports_c == 0)
 484                 ports[ports_c++] = SIP_PORT;
 485
 486         for (i = 0; i < ports_c; i++) {
 487                 /* Create helper structure */
 488                 memset(&sip[i], 0, sizeof(struct ip_conntrack_helper));
 489
 490                 sip[i].tuple.dst.protonum = IPPROTO_UDP;
 491                 sip[i].tuple.src.u.udp.port = htons(ports[i]);
 492                 sip[i].mask.src.u.udp.port = htons(0xFFFF);
 493                 sip[i].mask.dst.protonum = 0xFF;
 494                 sip[i].max_expected = 2;
 495                 sip[i].timeout = 3 * 60; /* 3 minutes */
 496                 sip[i].me = THIS_MODULE;
 497                 sip[i].help = sip_help;
 498
 499                 tmpname = &sip_names[i][0];
 500                 if (ports[i] == SIP_PORT)
 501                         sprintf(tmpname, "sip");
 502                 else
 503                         sprintf(tmpname, "sip-%d", i);
 504                 sip[i].name = tmpname;
 505
 506                 DEBUGP("port #%d: %d\n", i, ports[i]);
 507
 508                 ret = ip_conntrack_helper_register(&sip[i]);
 509                 if (ret) {
 510                         printk("ERROR registering helper for port %d\n",
 511                                 ports[i]);
 512                         fini();
 513                         return ret;
 514                 }
 515         }
 516         return 0;
 517 }
 518
 519 module_init(init);
 520 module_exit(fini);