src/src/transports/smtp_socks.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) Jeremy Harris 2015 - 2018 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 /* SOCKS version 5 proxy, client-mode */
   9
  10 #include "../exim.h"
  11 #include "smtp.h"
  12
  13 #ifdef SUPPORT_SOCKS /* entire file */
  14
  15 #ifndef nelem
  16 # define nelem(arr) (sizeof(arr)/sizeof(*arr))
  17 #endif
  18
  19
  20 /* Defaults */
  21 #define SOCKS_PORT      1080
  22 #define SOCKS_TIMEOUT   5
  23 #define SOCKS_WEIGHT    1
  24 #define SOCKS_PRIORITY  1
  25
  26 #define AUTH_NONE       0
  27 #define AUTH_NAME       2               /* user/password per RFC 1929 */
  28 #define AUTH_NAME_VER   1
  29
  30 struct socks_err
  31   {
  32   uschar *      reason;
  33   int           errcode;
  34   } socks_errs[] =
  35   {
  36     {NULL, 0},
  37     {US"general SOCKS server failure",          EIO},
  38     {US"connection not allowed by ruleset",     EACCES},
  39     {US"Network unreachable",                   ENETUNREACH},
  40     {US"Host unreachable",                      EHOSTUNREACH},
  41     {US"Connection refused",                    ECONNREFUSED},
  42     {US"TTL expired",                           ECANCELED},
  43     {US"Command not supported",                 EOPNOTSUPP},
  44     {US"Address type not supported",            EAFNOSUPPORT}
  45   };
  46
  47 typedef struct
  48   {
  49   const uschar *        proxy_host;
  50   uschar                auth_type;      /* RFC 1928 encoding */
  51   const uschar *        auth_name;
  52   const uschar *        auth_pwd;
  53   short                 port;
  54   BOOL                  is_failed;
  55   unsigned              timeout;
  56   unsigned              weight;
  57   unsigned              priority;
  58   } socks_opts;
  59
  60 static void
  61 socks_option_defaults(socks_opts * sob)
  62 {
  63 sob->proxy_host = NULL;
  64 sob->auth_type =  AUTH_NONE;
  65 sob->auth_name =  US"";
  66 sob->auth_pwd =   US"";
  67 sob->is_failed =  FALSE;
  68 sob->port =       SOCKS_PORT;
  69 sob->timeout =    SOCKS_TIMEOUT;
  70 sob->weight =     SOCKS_WEIGHT;
  71 sob->priority =   SOCKS_PRIORITY;
  72 }
  73
  74 static void
  75 socks_option(socks_opts * sob, const uschar * opt)
  76 {
  77 if (Ustrncmp(opt, "auth=", 5) == 0)
  78   {
  79   opt += 5;
  80   if (Ustrcmp(opt, "none") == 0)        sob->auth_type = AUTH_NONE;
  81   else if (Ustrcmp(opt, "name") == 0)   sob->auth_type = AUTH_NAME;
  82   }
  83 else if (Ustrncmp(opt, "name=", 5) == 0)
  84   sob->auth_name = opt + 5;
  85 else if (Ustrncmp(opt, "pass=", 5) == 0)
  86   sob->auth_pwd = opt + 5;
  87 else if (Ustrncmp(opt, "port=", 5) == 0)
  88   sob->port = atoi(CCS opt + 5);
  89 else if (Ustrncmp(opt, "tmo=", 4) == 0)
  90   sob->timeout = atoi(CCS opt + 4);
  91 else if (Ustrncmp(opt, "pri=", 4) == 0)
  92   sob->priority = atoi(CCS opt + 4);
  93 else if (Ustrncmp(opt, "weight=", 7) == 0)
  94   sob->weight = atoi(CCS opt + 7);
  95 return;
  96 }
  97
  98 static int
  99 socks_auth(int fd, int method, socks_opts * sob, time_t tmo)
 100 {
 101 uschar * s;
 102 int len, i, j;
 103
 104 switch(method)
 105   {
 106   default:
 107     log_write(0, LOG_MAIN|LOG_PANIC,
 108       "Unrecognised socks auth method %d", method);
 109     return FAIL;
 110   case AUTH_NONE:
 111     return OK;
 112   case AUTH_NAME:
 113     HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  socks auth NAME '%s' '%s'\n",
 114       sob->auth_name, sob->auth_pwd);
 115     i = Ustrlen(sob->auth_name);
 116     j = Ustrlen(sob->auth_pwd);
 117     s = string_sprintf("%c%c%.255s%c%.255s", AUTH_NAME_VER,
 118       i, sob->auth_name, j, sob->auth_pwd);
 119     len = i + j + 3;
 120     HDEBUG(D_transport|D_acl|D_v)
 121       {
 122       debug_printf_indent("  SOCKS>>");
 123       for (int i = 0; i<len; i++) debug_printf(" %02x", s[i]);
 124       debug_printf("\n");
 125       }
 126     if (send(fd, s, len, 0) < 0)
 127       return FAIL;
 128 #ifdef TCP_QUICKACK
 129     (void) setsockopt(fd, IPPROTO_TCP, TCP_QUICKACK, US &off, sizeof(off));
 130 #endif
 131     if (!fd_ready(fd, tmo) || read(fd, s, 2) != 2)
 132       return FAIL;
 133     HDEBUG(D_transport|D_acl|D_v)
 134       debug_printf_indent("  SOCKS<< %02x %02x\n", s[0], s[1]);
 135     if (s[0] == AUTH_NAME_VER && s[1] == 0)
 136       {
 137       HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  socks auth OK\n");
 138       return OK;
 139       }
 140
 141     log_write(0, LOG_MAIN|LOG_PANIC, "socks auth failed");
 142     errno = EPROTO;
 143     return FAIL;
 144   }
 145 }
 146
 147
 148
 149 /* Find a suitable proxy to use from the list.
 150 Possible common code with spamd_get_server() ?
 151
 152 Return: index into proxy spec array, or -1
 153 */
 154
 155 static int
 156 socks_get_proxy(socks_opts * proxies, unsigned nproxies)
 157 {
 158 unsigned int i;
 159 socks_opts * sd;
 160 socks_opts * lim = &proxies[nproxies];
 161 long rnd, weights;
 162 unsigned pri;
 163 static BOOL srandomed = FALSE;
 164
 165 if (nproxies == 1)              /* shortcut, if we have only 1 server */
 166   return (proxies[0].is_failed ? -1 : 0);
 167
 168 /* init random */
 169 if (!srandomed)
 170   {
 171   struct timeval tv;
 172   gettimeofday(&tv, NULL);
 173   srandom((unsigned int)(tv.tv_usec/1000));
 174   srandomed = TRUE;
 175   }
 176
 177 /* scan for highest pri */
 178 for (pri = 0, sd = proxies; sd < lim; sd++)
 179   if (!sd->is_failed && sd->priority > pri)
 180     pri = sd->priority;
 181
 182 /* get sum of weights at this pri */
 183 for (weights = 0, sd = proxies; sd < lim; sd++)
 184   if (!sd->is_failed && sd->priority == pri)
 185     weights += sd->weight;
 186 if (weights == 0)       /* all servers failed */
 187   return -1;
 188
 189 for (rnd = random() % weights, i = 0; i < nproxies; i++)
 190   {
 191   sd = &proxies[i];
 192   if (!sd->is_failed && sd->priority == pri)
 193     if ((rnd -= sd->weight) <= 0)
 194       return i;
 195   }
 196
 197 log_write(0, LOG_MAIN|LOG_PANIC,
 198   "%s unknown error (memory/cpu corruption?)", __FUNCTION__);
 199 return -1;
 200 }
 201
 202
 203
 204 /* Make a connection via a socks proxy
 205
 206 Arguments:
 207  host           smtp target host
 208  host_af        address family
 209  port           remote tcp port number
 210  interface      local interface
 211  tb             transport
 212  timeout        connection timeout (zero for indefinite)
 213
 214 Return value:
 215  0 on success; -1 on failure, with errno set
 216 */
 217
 218 int
 219 socks_sock_connect(host_item * host, int host_af, int port, uschar * interface,
 220   transport_instance * tb, int timeout)
 221 {
 222 smtp_transport_options_block * ob =
 223   (smtp_transport_options_block *)tb->options_block;
 224 const uschar * proxy_list;
 225 const uschar * proxy_spec;
 226 int sep = 0;
 227 int fd;
 228 time_t tmo;
 229 const uschar * state;
 230 uschar buf[24];
 231 socks_opts proxies[32];                 /* max #proxies handled */
 232 unsigned nproxies;
 233 socks_opts * sob;
 234 unsigned size;
 235 blob early_data;
 236
 237 if (!timeout) timeout = 24*60*60;       /* use 1 day for "indefinite" */
 238 tmo = time(NULL) + timeout;
 239
 240 if (!(proxy_list = expand_string(ob->socks_proxy)))
 241   {
 242   log_write(0, LOG_MAIN|LOG_PANIC, "Bad expansion for socks_proxy in %s",
 243     tb->name);
 244   return -1;
 245   }
 246
 247 /* Read proxy list */
 248
 249 for (nproxies = 0;
 250         nproxies < nelem(proxies)
 251      && (proxy_spec = string_nextinlist(&proxy_list, &sep, NULL, 0));
 252      nproxies++)
 253   {
 254   int subsep = -' ';
 255   const uschar * option;
 256
 257   socks_option_defaults(sob = &proxies[nproxies]);
 258
 259   if (!(sob->proxy_host = string_nextinlist(&proxy_spec, &subsep, NULL, 0)))
 260     {
 261     /* paniclog config error */
 262     return -1;
 263     }
 264
 265   /*XXX consider global options eg. "hide socks_password = wibble" on the tpt */
 266   /* extract any further per-proxy options */
 267   while ((option = string_nextinlist(&proxy_spec, &subsep, NULL, 0)))
 268     socks_option(sob, option);
 269   }
 270
 271 /* Set up the socks protocol method-selection message,
 272 for sending on connection */
 273
 274 state = US"method select";
 275 buf[0] = 5; buf[1] = 1; buf[2] = sob->auth_type;
 276 early_data.data = buf;
 277 early_data.len = 3;
 278
 279 /* Try proxies until a connection succeeds */
 280
 281 for(;;)
 282   {
 283   int idx;
 284   host_item proxy;
 285   int proxy_af;
 286
 287   if ((idx = socks_get_proxy(proxies, nproxies)) < 0)
 288     {
 289     HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  no proxies left\n");
 290     errno = EBUSY;
 291     return -1;
 292     }
 293   sob = &proxies[idx];
 294
 295   /* bodge up a host struct for the proxy */
 296   proxy.address = proxy.name = sob->proxy_host;
 297   proxy_af = Ustrchr(sob->proxy_host, ':') ? AF_INET6 : AF_INET;
 298
 299   /*XXX we trust that the method-select command is idempotent */
 300   if ((fd = smtp_sock_connect(&proxy, proxy_af, sob->port,
 301               interface, tb, sob->timeout, &early_data)) >= 0)
 302     {
 303     proxy_local_address = string_copy(proxy.address);
 304     proxy_local_port = sob->port;
 305     break;
 306     }
 307
 308   log_write(0, LOG_MAIN, "%s: %s", __FUNCTION__, strerror(errno));
 309   sob->is_failed = TRUE;
 310   }
 311
 312 /* Do the socks protocol stuff */
 313
 314 HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SOCKS>> 05 01 %02x\n", sob->auth_type);
 315
 316 /* expect method response */
 317
 318 #ifdef TCP_QUICKACK
 319 (void) setsockopt(fd, IPPROTO_TCP, TCP_QUICKACK, US &off, sizeof(off));
 320 #endif
 321
 322 if (  !fd_ready(fd, tmo)
 323    || read(fd, buf, 2) != 2
 324    )
 325   goto rcv_err;
 326 HDEBUG(D_transport|D_acl|D_v)
 327   debug_printf_indent("  SOCKS<< %02x %02x\n", buf[0], buf[1]);
 328 if (  buf[0] != 5
 329    || socks_auth(fd, buf[1], sob, tmo) != OK
 330    )
 331   goto proxy_err;
 332
 333   {
 334   union sockaddr_46 sin;
 335   (void) ip_addr(&sin, host_af, host->address, port);
 336
 337   /* send connect (ipver, ipaddr, port) */
 338
 339   buf[0] = 5; buf[1] = 1; buf[2] = 0; buf[3] = host_af == AF_INET6 ? 4 : 1;
 340   #if HAVE_IPV6
 341   if (host_af == AF_INET6)
 342     {
 343     memcpy(buf+4, &sin.v6.sin6_addr,       sizeof(sin.v6.sin6_addr));
 344     memcpy(buf+4+sizeof(sin.v6.sin6_addr),
 345       &sin.v6.sin6_port, sizeof(sin.v6.sin6_port));
 346     size = 4+sizeof(sin.v6.sin6_addr)+sizeof(sin.v6.sin6_port);
 347     }
 348   else
 349   #endif
 350     {
 351     memcpy(buf+4, &sin.v4.sin_addr.s_addr, sizeof(sin.v4.sin_addr.s_addr));
 352     memcpy(buf+4+sizeof(sin.v4.sin_addr.s_addr),
 353       &sin.v4.sin_port, sizeof(sin.v4.sin_port));
 354     size = 4+sizeof(sin.v4.sin_addr.s_addr)+sizeof(sin.v4.sin_port);
 355     }
 356   }
 357
 358 state = US"connect";
 359 HDEBUG(D_transport|D_acl|D_v)
 360   {
 361   debug_printf_indent("  SOCKS>>");
 362   for (int i = 0; i<size; i++) debug_printf(" %02x", buf[i]);
 363   debug_printf("\n");
 364   }
 365 if (send(fd, buf, size, 0) < 0)
 366   goto snd_err;
 367
 368 /* expect conn-reply (success, local(ipver, addr, port))
 369 of same length as conn-request, or non-success fail code */
 370
 371 if (  !fd_ready(fd, tmo)
 372    || (size = read(fd, buf, size)) < 2
 373    )
 374   goto rcv_err;
 375 HDEBUG(D_transport|D_acl|D_v)
 376   {
 377   debug_printf_indent("  SOCKS>>");
 378   for (int i = 0; i<size; i++) debug_printf(" %02x", buf[i]);
 379   debug_printf("\n");
 380   }
 381 if (  buf[0] != 5
 382    || buf[1] != 0
 383    )
 384   goto proxy_err;
 385
 386 proxy_external_address = string_copy(
 387   host_ntoa(buf[3] == 4 ? AF_INET6 : AF_INET, buf+4, NULL, NULL));
 388 proxy_external_port = ntohs(*((uint16_t *)(buf + (buf[3] == 4 ? 20 : 8))));
 389 proxy_session = TRUE;
 390
 391 HDEBUG(D_transport|D_acl|D_v)
 392   debug_printf_indent("  proxy farside: [%s]:%d\n", proxy_external_address, proxy_external_port);
 393
 394 return fd;
 395
 396 snd_err:
 397   HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  proxy snd_err %s: %s\n", state, strerror(errno));
 398   return -1;
 399
 400 proxy_err:
 401   {
 402   struct socks_err * se =
 403     buf[1] > nelem(socks_errs) ? NULL : socks_errs + buf[1];
 404   HDEBUG(D_transport|D_acl|D_v)
 405     debug_printf_indent("  proxy %s: %s\n", state, se ? se->reason : US"unknown error code received");
 406   errno = se ? se->errcode : EPROTO;
 407   }
 408
 409 rcv_err:
 410   HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  proxy rcv_err %s: %s\n", state, strerror(errno));
 411   if (!errno) errno = EPROTO;
 412   else if (errno == ENOENT) errno = ECONNABORTED;
 413   return -1;
 414 }
 415
 416 #endif  /* entire file */
 417 /* vi: aw ai sw=2
 418 */