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