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 int ct_sip_get_info(const char *dptr, size_t dlen,
  56                                 unsigned int *matchoff,
  57                                 unsigned int *matchlen,
  58                                 struct sip_header_nfo *hnfo);
  59 EXPORT_SYMBOL_GPL(ct_sip_get_info);
  60
  61
  62 static int digits_len(const char *dptr, const char *limit, int *shift);
  63 static int epaddr_len(const char *dptr, const char *limit, int *shift);
  64 static int skp_digits_len(const char *dptr, const char *limit, int *shift);
  65 static int skp_epaddr_len(const char *dptr, const char *limit, int *shift);
  66
  67 struct sip_header_nfo ct_sip_hdrs[] = {
  68         {       /* Via header */
  69                 .lname          = "Via:",
  70                 .lnlen          = sizeof("Via:") - 1,
  71                 .sname          = "\r\nv:",
  72                 .snlen          = sizeof("\r\nv:") - 1, /* rfc3261 "\r\n" */
  73                 .ln_str         = "UDP ",
  74                 .ln_strlen      = sizeof("UDP ") - 1,
  75                 .match_len      = epaddr_len,
  76         },
  77         {       /* Contact header */
  78                 .lname          = "Contact:",
  79                 .lnlen          = sizeof("Contact:") - 1,
  80                 .sname          = "\r\nm:",
  81                 .snlen          = sizeof("\r\nm:") - 1,
  82                 .ln_str         = "sip:",
  83                 .ln_strlen      = sizeof("sip:") - 1,
  84                 .match_len      = skp_epaddr_len
  85         },
  86         {       /* Content length header */
  87                 .lname          = "Content-Length:",
  88                 .lnlen          = sizeof("Content-Length:") - 1,
  89                 .sname          = "\r\nl:",
  90                 .snlen          = sizeof("\r\nl:") - 1,
  91                 .ln_str         = ":",
  92                 .ln_strlen      = sizeof(":") - 1,
  93                 .match_len      = skp_digits_len
  94         },
  95         {       /* SDP media info */
  96                 .lname          = "\nm=",
  97                 .lnlen          = sizeof("\nm=") - 1,
  98                 .sname          = "\rm=",
  99                 .snlen          = sizeof("\rm=") - 1,
 100                 .ln_str         = "audio ",
 101                 .ln_strlen      = sizeof("audio ") - 1,
 102                 .match_len      = digits_len
 103         },
 104         {       /* SDP owner address*/
 105                 .lname          = "\no=",
 106                 .lnlen          = sizeof("\no=") - 1,
 107                 .sname          = "\ro=",
 108                 .snlen          = sizeof("\ro=") - 1,
 109                 .ln_str         = "IN IP4 ",
 110                 .ln_strlen      = sizeof("IN IP4 ") - 1,
 111                 .match_len      = epaddr_len
 112         },
 113         {       /* SDP connection info */
 114                 .lname          = "\nc=",
 115                 .lnlen          = sizeof("\nc=") - 1,
 116                 .sname          = "\rc=",
 117                 .snlen          = sizeof("\rc=") - 1,
 118                 .ln_str         = "IN IP4 ",
 119                 .ln_strlen      = sizeof("IN IP4 ") - 1,
 120                 .match_len      = epaddr_len
 121         },
 122         {       /* Requests headers */
 123                 .lname          = "sip:",
 124                 .lnlen          = sizeof("sip:") - 1,
 125                 .sname          = "sip:",
 126                 .snlen          = sizeof("sip:") - 1, /* yes, i know.. ;) */
 127                 .ln_str         = "@",
 128                 .ln_strlen      = sizeof("@") - 1,
 129                 .match_len      = epaddr_len
 130         },
 131         {       /* SDP version header */
 132                 .lname          = "\nv=",
 133                 .lnlen          = sizeof("\nv=") - 1,
 134                 .sname          = "\rv=",
 135                 .snlen          = sizeof("\rv=") - 1,
 136                 .ln_str         = "=",
 137                 .ln_strlen      = sizeof("=") - 1,
 138                 .match_len      = digits_len
 139         }
 140 };
 141 EXPORT_SYMBOL_GPL(ct_sip_hdrs);
 142
 143 /* get line lenght until first CR or LF seen. */
 144 int ct_sip_lnlen(const char *line, const char *limit)
 145 {
 146         const char *k = line;
 147
 148         while ((line <= limit) && (*line == '\r' || *line == '\n'))
 149                 line++;
 150
 151         while (line <= limit) {
 152                 if (*line == '\r' || *line == '\n')
 153                         break;
 154                 line++;
 155         }
 156         return line - k;
 157 }
 158 EXPORT_SYMBOL_GPL(ct_sip_lnlen);
 159
 160 /* Linear string search, case sensitive. */
 161 const char *ct_sip_search(const char *needle, const char *haystack,
 162                           size_t needle_len, size_t haystack_len)
 163 {
 164         const char *limit = haystack + (haystack_len - needle_len);
 165
 166         while (haystack <= limit) {
 167                 if (memcmp(haystack, needle, needle_len) == 0)
 168                         return haystack;
 169                 haystack++;
 170         }
 171         return NULL;
 172 }
 173 EXPORT_SYMBOL_GPL(ct_sip_search);
 174
 175 static int digits_len(const char *dptr, const char *limit, int *shift)
 176 {
 177         int len = 0;
 178         while (dptr <= limit && isdigit(*dptr)) {
 179                 dptr++;
 180                 len++;
 181         }
 182         return len;
 183 }
 184
 185 /* get digits lenght, skiping blank spaces. */
 186 static int skp_digits_len(const char *dptr, const char *limit, int *shift)
 187 {
 188         for (; dptr <= limit && *dptr == ' '; dptr++)
 189                 (*shift)++;
 190
 191         return digits_len(dptr, limit, shift);
 192 }
 193
 194 /* Simple ipaddr parser.. */
 195 static int parse_ipaddr(const char *cp, const char **endp,
 196                         u_int32_t *ipaddr, const char *limit)
 197 {
 198         unsigned long int val;
 199         int i, digit = 0;
 200
 201         for (i = 0, *ipaddr = 0; cp <= limit && i < 4; i++) {
 202                 digit = 0;
 203                 if (!isdigit(*cp))
 204                         break;
 205
 206                 val = simple_strtoul(cp, (char **)&cp, 10);
 207                 if (val > 0xFF)
 208                         return -1;
 209
 210                 ((u_int8_t *)ipaddr)[i] = val;
 211                 digit = 1;
 212
 213                 if (*cp != '.')
 214                         break;
 215                 cp++;
 216         }
 217         if (!digit)
 218                 return -1;
 219
 220         if (endp)
 221                 *endp = cp;
 222
 223         return 0;
 224 }
 225
 226 /* skip ip address. returns it lenght. */
 227 static int epaddr_len(const char *dptr, const char *limit, int *shift)
 228 {
 229         const char *aux = dptr;
 230         u_int32_t ip;
 231
 232         if (parse_ipaddr(dptr, &dptr, &ip, limit) < 0) {
 233                 DEBUGP("ip: %s parse failed.!\n", dptr);
 234                 return 0;
 235         }
 236
 237         /* Port number */
 238         if (*dptr == ':') {
 239                 dptr++;
 240                 dptr += digits_len(dptr, limit, shift);
 241         }
 242         return dptr - aux;
 243 }
 244
 245 /* get address length, skiping user info. */
 246 static int skp_epaddr_len(const char *dptr, const char *limit, int *shift)
 247 {
 248         int s = *shift;
 249
 250         for (; dptr <= limit && *dptr != '@'; dptr++)
 251                 (*shift)++;
 252
 253         if (*dptr == '@') {
 254                 dptr++;
 255                 (*shift)++;
 256         } else
 257                 *shift = s;
 258
 259         return epaddr_len(dptr, limit, shift);
 260 }
 261
 262 /* Returns 0 if not found, -1 error parsing. */
 263 int ct_sip_get_info(const char *dptr, size_t dlen,
 264                     unsigned int *matchoff,
 265                     unsigned int *matchlen,
 266                     struct sip_header_nfo *hnfo)
 267 {
 268         const char *limit, *aux, *k = dptr;
 269         int shift = 0;
 270
 271         limit = dptr + (dlen - hnfo->lnlen);
 272
 273         while (dptr <= limit) {
 274                 if ((strncmp(dptr, hnfo->lname, hnfo->lnlen) != 0) &&
 275                     (strncmp(dptr, hnfo->sname, hnfo->snlen) != 0)) {
 276                         dptr++;
 277                         continue;
 278                 }
 279                 aux = ct_sip_search(hnfo->ln_str, dptr, hnfo->ln_strlen,
 280                                     ct_sip_lnlen(dptr, limit));
 281                 if (!aux) {
 282                         DEBUGP("'%s' not found in '%s'.\n", hnfo->ln_str,
 283                                hnfo->lname);
 284                         return -1;
 285                 }
 286                 aux += hnfo->ln_strlen;
 287
 288                 *matchlen = hnfo->match_len(aux, limit, &shift);
 289                 if (!*matchlen)
 290                         return -1;
 291
 292                 *matchoff = (aux - k) + shift;
 293
 294                 DEBUGP("%s match succeeded! - len: %u\n", hnfo->lname,
 295                        *matchlen);
 296                 return 1;
 297         }
 298         DEBUGP("%s header not found.\n", hnfo->lname);
 299         return 0;
 300 }
 301
 302 static int set_expected_rtp(struct sk_buff **pskb,
 303                             struct ip_conntrack *ct,
 304                             enum ip_conntrack_info ctinfo,
 305                             u_int32_t ipaddr, u_int16_t port,
 306                             const char *dptr)
 307 {
 308         struct ip_conntrack_expect *exp;
 309         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 310         int ret;
 311
 312         exp = ip_conntrack_expect_alloc(ct);
 313         if (exp == NULL)
 314                 return NF_DROP;
 315
 316         exp->tuple.src.ip = ct->tuplehash[!dir].tuple.src.ip;
 317         exp->tuple.src.u.udp.port = 0;
 318         exp->tuple.dst.ip = ipaddr;
 319         exp->tuple.dst.u.udp.port = htons(port);
 320         exp->tuple.dst.protonum = IPPROTO_UDP;
 321
 322         exp->mask.src.ip = 0xFFFFFFFF;
 323         exp->mask.src.u.udp.port = 0;
 324         exp->mask.dst.ip = 0xFFFFFFFF;
 325         exp->mask.dst.u.udp.port = 0xFFFF;
 326         exp->mask.dst.protonum = 0xFF;
 327
 328         exp->expectfn = NULL;
 329         exp->flags = 0;
 330
 331         if (ip_nat_sdp_hook)
 332                 ret = ip_nat_sdp_hook(pskb, ctinfo, exp, dptr);
 333         else {
 334                 if (ip_conntrack_expect_related(exp) != 0)
 335                         ret = NF_DROP;
 336                 else
 337                         ret = NF_ACCEPT;
 338         }
 339         ip_conntrack_expect_put(exp);
 340
 341         return ret;
 342 }
 343
 344 static int sip_help(struct sk_buff **pskb,
 345                     struct ip_conntrack *ct,
 346                     enum ip_conntrack_info ctinfo)
 347 {
 348         unsigned int dataoff, datalen;
 349         const char *dptr;
 350         int ret = NF_ACCEPT;
 351         int matchoff, matchlen;
 352         u_int32_t ipaddr;
 353         u_int16_t port;
 354
 355         /* No Data ? */
 356         dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
 357         if (dataoff >= (*pskb)->len) {
 358                 DEBUGP("skb->len = %u\n", (*pskb)->len);
 359                 return NF_ACCEPT;
 360         }
 361
 362         ip_ct_refresh(ct, *pskb, sip_timeout * HZ);
 363
 364         if (!skb_is_nonlinear(*pskb))
 365                 dptr = (*pskb)->data + dataoff;
 366         else {
 367                 DEBUGP("Copy of skbuff not supported yet.\n");
 368                 goto out;
 369         }
 370
 371         if (ip_nat_sip_hook) {
 372                 if (!ip_nat_sip_hook(pskb, ctinfo, ct, &dptr)) {
 373                         ret = NF_DROP;
 374                         goto out;
 375                 }
 376         }
 377
 378         /* After this point NAT, could have mangled skb, so
 379            we need to recalculate payload lenght. */
 380         datalen = (*pskb)->len - dataoff;
 381
 382         if (datalen < (sizeof("SIP/2.0 200") - 1))
 383                 goto out;
 384
 385         /* RTP info only in some SDP pkts */
 386         if (memcmp(dptr, "INVITE", sizeof("INVITE") - 1) != 0 &&
 387             memcmp(dptr, "SIP/2.0 200", sizeof("SIP/2.0 200") - 1) != 0) {
 388                 goto out;
 389         }
 390         /* Get ip and port address from SDP packet. */
 391         if (ct_sip_get_info(dptr, datalen, &matchoff, &matchlen,
 392                             &ct_sip_hdrs[POS_CONNECTION]) > 0) {
 393
 394                 /* We'll drop only if there are parse problems. */
 395                 if (parse_ipaddr(dptr + matchoff, NULL, &ipaddr,
 396                                  dptr + datalen) < 0) {
 397                         ret = NF_DROP;
 398                         goto out;
 399                 }
 400                 if (ct_sip_get_info(dptr, datalen, &matchoff, &matchlen,
 401                                     &ct_sip_hdrs[POS_MEDIA]) > 0) {
 402
 403                         port = simple_strtoul(dptr + matchoff, NULL, 10);
 404                         if (port < 1024) {
 405                                 ret = NF_DROP;
 406                                 goto out;
 407                         }
 408                         ret = set_expected_rtp(pskb, ct, ctinfo,
 409                                                ipaddr, port, dptr);
 410                 }
 411         }
 412 out:
 413         return ret;
 414 }
 415
 416 static struct ip_conntrack_helper sip[MAX_PORTS];
 417 static char sip_names[MAX_PORTS][10];
 418
 419 static void fini(void)
 420 {
 421         int i;
 422         for (i = 0; i < ports_c; i++) {
 423                 DEBUGP("unregistering helper for port %d\n", ports[i]);
 424                 ip_conntrack_helper_unregister(&sip[i]);
 425         }
 426 }
 427
 428 static int __init init(void)
 429 {
 430         int i, ret;
 431         char *tmpname;
 432
 433         if (ports_c == 0)
 434                 ports[ports_c++] = SIP_PORT;
 435
 436         for (i = 0; i < ports_c; i++) {
 437                 /* Create helper structure */
 438                 memset(&sip[i], 0, sizeof(struct ip_conntrack_helper));
 439
 440                 sip[i].tuple.dst.protonum = IPPROTO_UDP;
 441                 sip[i].tuple.src.u.udp.port = htons(ports[i]);
 442                 sip[i].mask.src.u.udp.port = 0xFFFF;
 443                 sip[i].mask.dst.protonum = 0xFF;
 444                 sip[i].max_expected = 2;
 445                 sip[i].timeout = 3 * 60; /* 3 minutes */
 446                 sip[i].me = THIS_MODULE;
 447                 sip[i].help = sip_help;
 448
 449                 tmpname = &sip_names[i][0];
 450                 if (ports[i] == SIP_PORT)
 451                         sprintf(tmpname, "sip");
 452                 else
 453                         sprintf(tmpname, "sip-%d", i);
 454                 sip[i].name = tmpname;
 455
 456                 DEBUGP("port #%d: %d\n", i, ports[i]);
 457
 458                 ret = ip_conntrack_helper_register(&sip[i]);
 459                 if (ret) {
 460                         printk("ERROR registering helper for port %d\n",
 461                                 ports[i]);
 462                         fini();
 463                         return ret;
 464                 }
 465         }
 466         return 0;
 467 }
 468
 469 module_init(init);
 470 module_exit(fini);