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