mdw@git.distorted.org.uk Git - become/blob - src/check.c

   1 /* -*-c-*-
   2  *
   3  * $Id: check.c,v 1.14 2004/04/17 10:46:08 mdw Exp $
   4  *
   5  * Check validity of requests
   6  *
   7  * (c) 1998 EBI
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of `become'
  13  *
  14  * `Become' is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU General Public License as published by
  16  * the Free Software Foundation; either version 2 of the License, or
  17  * (at your option) any later version.
  18  *
  19  * `Become' is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with `become'; if not, write to the Free Software Foundation,
  26  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  27  */
  28
  29 /*----- Header files ------------------------------------------------------*/
  30
  31 /* --- ANSI headers --- */
  32
  33 #include <ctype.h>
  34 #include <errno.h>
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <time.h>
  39
  40 /* --- Unix headers --- */
  41
  42 #include <sys/time.h>
  43 #include <sys/types.h>
  44 #include <sys/socket.h>
  45
  46 #include <netinet/in.h>
  47
  48 #include <arpa/inet.h>
  49
  50 #include <fcntl.h>
  51 #include <netdb.h>
  52 #include <unistd.h>
  53
  54 /* --- mLib headers --- */
  55
  56 #include <mLib/alloc.h>
  57 #include <mLib/quis.h>
  58 #include <mLib/report.h>
  59 #include <mLib/sym.h>
  60 #include <mLib/trace.h>
  61
  62 /* --- Catacomb headers --- */
  63
  64 #include <catacomb/buf.h>
  65 #include <catacomb/gdsa.h>
  66 #include <catacomb/key.h>
  67 #include <catacomb/dh.h>
  68 #include <catacomb/ec-keys.h>
  69 #include <catacomb/mp.h>
  70 #include <catacomb/noise.h>
  71 #include <catacomb/rand.h>
  72
  73 /* --- Local headers --- */
  74
  75 #include "become.h"
  76 #include "config.h"
  77 #include "lexer.h"
  78 #include "name.h"
  79 #include "netg.h"
  80 #include "rule.h"
  81 #include "parse.h"
  82 #include "userdb.h"
  83
  84 /*----- Client-end network support ----------------------------------------*/
  85
  86 #ifndef NONETWORK
  87
  88 /* --- @check__send@ --- *
  89  *
  90  * Arguments:   @char *buf@ = pointer to encrypted request
  91  *              @size_t sz@ = size of request
  92  *              @int fd@ = socket to send from
  93  *              @struct sockaddr_in *serv@ = pointer to table of servers
  94  *              @size_t n_serv@ = number of servers
  95  *
  96  * Returns:     ---
  97  *
  98  * Use:         Sends the request packet to the list of servers.  If the
  99  *              message couldn't be sent to any of them, an error is
 100  *              reported.
 101  */
 102
 103 static void check__send(char *buf, size_t sz, int fd,
 104                         struct sockaddr_in *serv, size_t n_serv)
 105 {
 106   size_t i;
 107   int ok = 0;
 108   int err = 0;
 109
 110   for (i = 0; i < n_serv; i++) {
 111     if (sendto(fd, buf, sz, 0,
 112                (struct sockaddr *)(serv + i), sizeof(serv[i])) < 0) {
 113       T( trace(TRACE_CLIENT, "client: send to %s failed: %s",
 114                inet_ntoa(serv[i].sin_addr), strerror(errno)); )
 115       err = errno;
 116     } else
 117       ok = 1;
 118   }
 119
 120   if (!ok)
 121     die(1, "couldn't send request to server: %s", strerror(err));
 122 }
 123
 124 /* --- @check__ask@ --- *
 125  *
 126  * Arguments:   @request *rq@ = pointer to request buffer
 127  *              @struct sockaddr_in *serv@ = pointer to table of servers
 128  *              @size_t n_serv@ = number of servers
 129  *
 130  * Returns:     Nonzero if OK, zero if forbidden
 131  *
 132  * Use:         Contacts a number of servers to decide whether the request
 133  *              is OK.
 134  */
 135
 136 static int check__ask(request *rq, struct sockaddr_in *serv, size_t n_serv)
 137 {
 138   static int tbl[] = { 0, 5, 10, 20, -1 };
 139
 140   char buff[2048], rbuff[2048];
 141   size_t rqlen;
 142   gdsa g;
 143   const char *p;
 144   ghash *h;
 145   key_packdef *kp;
 146   buf b;
 147   int fd;
 148   struct sockaddr_in sin;
 149   socklen_t slen;
 150   ssize_t sz;
 151   int ans;
 152   fd_set fds;
 153   struct timeval start, now, tv;
 154   gdsa_sig s;
 155   key_file f;
 156   key *k;
 157   key_iter ki;
 158   int ind;
 159   size_t i;
 160
 161   /* --- Open the public keyring --- */
 162
 163   if ((key_open(&f, file_PUBKEY, KOPEN_READ, key_moan, 0)) != 0)
 164     die(1, "couldn't open public keyring");
 165
 166   /* --- Build the request packet --- */
 167
 168   rand_noisesrc(RAND_GLOBAL, &noise_source);
 169   rand_seed(RAND_GLOBAL, 160);
 170   buf_init(&b, buff, sizeof(buff));
 171   rand_get(RAND_GLOBAL, buf_get(&b, 64), 64);
 172   buf_putu32(&b, rq->from);
 173   buf_putu32(&b, rq->to);
 174   buf_putu16(&b, strlen(rq->cmd));
 175   buf_put(&b, rq->cmd, strlen(rq->cmd));
 176   rqlen = BLEN(&b);
 177
 178   /* --- Create my socket --- */
 179
 180   if ((fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
 181     die(1, "couldn't create socket: %s", strerror(errno));
 182   if (fcntl(fd, F_SETFD, 1) < 0)
 183     die(1, "couldn't set close-on-exec flag for socket: %s", strerror(errno));
 184
 185   /* --- Bind myself to some address --- */
 186
 187   sin.sin_family = AF_INET;
 188   sin.sin_port = 0;
 189   sin.sin_addr.s_addr = htonl(INADDR_ANY);
 190
 191   if (bind(fd, (struct sockaddr *)&sin, sizeof(sin)) < 0)
 192     die(1, "couldn't bind socket to address: %s", strerror(errno));
 193
 194   /* --- Find out when we are --- */
 195
 196   gettimeofday(&start, 0);
 197   ind = 0;
 198
 199   /* --- Now loop until everything's done --- */
 200
 201   for (;;) {
 202     gettimeofday(&now, 0);
 203
 204     /* --- If the current timer has expired, find one that hasn't --- *
 205      *
 206      * Also resend the request after I've found a timer which is still
 207      * extant.  If there aren't any, report an error.
 208      */
 209
 210     if (now.tv_sec >= start.tv_sec + tbl[ind] &&
 211         now.tv_usec >= start.tv_usec) {
 212       do {
 213         ind++;
 214         if (tbl[ind] < 0)
 215           die(1, "no reply from servers");
 216       } while (now.tv_sec >= start.tv_sec + tbl[ind] &&
 217                now.tv_usec >= start.tv_usec);
 218       check__send(buff, rqlen, fd, serv, n_serv);
 219       T( trace(TRACE_CLIENT, "client: send request to servers"); )
 220     }
 221
 222     /* --- Now wait for a packet to arrive --- */
 223
 224     if (now.tv_usec > start.tv_usec) {
 225       now.tv_usec -= 1000000;
 226       now.tv_sec += 1;
 227     }
 228     tv.tv_sec = start.tv_sec + tbl[ind] - now.tv_sec;
 229     tv.tv_usec = start.tv_usec - now.tv_usec;
 230
 231     /* --- Sort out file descriptors to watch --- */
 232
 233     FD_ZERO(&fds);
 234     FD_SET(fd, &fds);
 235
 236     /* --- Wait for them --- */
 237
 238     i = select(FD_SETSIZE, &fds, 0, 0, &tv);
 239     if (i == 0 || (i < 0 && errno == EINTR))
 240       continue;
 241     if (i < 0)
 242       die(1, "error waiting for reply: %s", strerror(errno));
 243
 244     /* --- Read the reply data --- */
 245
 246     slen = sizeof(sin);
 247     if ((sz = recvfrom(fd, (char *)rbuff, sizeof(rbuff), 0,
 248                        (struct sockaddr *)&sin, &slen)) < 0)
 249       die(1, "error reading server's reply: %s", strerror(errno));
 250
 251     IF_TRACING(TRACE_CLIENT, {
 252       struct hostent *h = gethostbyaddr((char *)&sin.sin_addr,
 253                                         sizeof(sin.sin_addr), AF_INET);
 254       trace(TRACE_CLIENT, "client: reply received from %s port %i",
 255             h ? h->h_name : inet_ntoa(sin.sin_addr),
 256             ntohs(sin.sin_port));
 257     })
 258
 259     /* --- Verify the sender --- *
 260      *
 261      * This is more to avoid confusion than for security: an active
 262      * attacker is quite capable of forging the source address.  We rely
 263      * on the signature in the reply packet for authentication.
 264      */
 265
 266     for (i = 0; i < n_serv; i++) {
 267       if (sin.sin_addr.s_addr == serv[i].sin_addr.s_addr &&
 268           sin.sin_port == serv[i].sin_port)
 269         break;
 270     }
 271     if (i >= n_serv) {
 272       T( trace(TRACE_CLIENT, "client: reply from unknown host"); )
 273       continue;
 274     }
 275
 276     /* --- The hash length varies with the key --- *
 277      *
 278      * So we have to unpack once for each key.  This isn't too bad.
 279      */
 280
 281     g.r = &rand_global;
 282     g.u = 0;
 283     key_mkiter(&ki, &f);
 284     while ((k = key_next(&ki)) != 0) {
 285       if (key_expired(k)) continue;
 286       if (strcmp(k->type, "become") != 0) continue;
 287
 288       /* --- Get a hash function --- */
 289
 290       if ((p = key_getattr(&f, k, "hash")) == 0)
 291         p = "sha";
 292       if ((g.h = ghash_byname(p)) == 0)
 293         continue;
 294
 295       /* --- Unpack the key --- */
 296
 297       p = key_getattr(&f, k, "sig");
 298       if (!p || strcmp(p, "dsa") == 0) {
 299         dh_pub dp;
 300         kp = key_fetchinit(dh_pubfetch, 0, &dp);
 301         if (key_fetch(kp, k)) goto fail_1;
 302         if ((g.g = group_prime(&dp.dp)) == 0) goto fail_1;
 303         g.p = G_CREATE(g.g);
 304         if (G_FROMINT(g.g, g.p, dp.y)) goto fail_2;
 305       } else if (strcmp(p, "ecdsa") == 0) {
 306         ec_pub ep;
 307         ec_info ei;
 308         kp = key_fetchinit(ec_pubfetch, 0, &ep);
 309         if (key_fetch(kp, k)) goto fail_1;
 310         if (ec_getinfo(&ei, ep.cstr)) goto fail_1;
 311         g.g = group_ec(&ei);
 312         g.p = G_CREATE(g.g);
 313         if (G_FROMEC(g.g, g.p, &ep.p)) goto fail_2;
 314       } else
 315         goto fail_0;
 316
 317       /* --- Unpack the response --- */
 318
 319       h = GH_INIT(g.h);
 320       GH_HASH(h, buff, rqlen);
 321       buf_init(&b, rbuff, sz);
 322       if (buf_ensure(&b, g.h->hashsz)) goto fail_3;
 323       if (memcmp(BCUR(&b), GH_DONE(h, 0), g.h->hashsz) != 0) goto fail_3;
 324       BSTEP(&b, g.h->hashsz);
 325       if ((ans = buf_getbyte(&b)) < 0) goto fail_3;
 326       GH_DESTROY(h);
 327
 328       /* --- Verify the signature --- */
 329
 330       h = gdsa_beginhash(&g);
 331       GH_HASH(h, BBASE(&b), BLEN(&b));
 332       gdsa_endhash(&g, h);
 333       s.r = s.s = 0;
 334       if ((s.r = buf_getmp(&b)) == 0 ||
 335           (s.s = buf_getmp(&b)) == 0)
 336         goto fail_4;
 337       if (gdsa_verify(&g, &s, GH_DONE(h, 0)))
 338         goto fail_4;
 339
 340       mp_drop(s.r); mp_drop(s.s);
 341       GH_DESTROY(h);
 342       G_DESTROY(g.g, g.p);
 343       G_DESTROYGROUP(g.g);
 344       key_fetchdone(kp);
 345       key_close(&f);
 346       return (ans);
 347
 348       /* --- Tidy up and try again --- */
 349
 350     fail_4:
 351       mp_drop(s.r); mp_drop(s.s);
 352     fail_3:
 353       GH_DESTROY(h);
 354       G_DESTROY(g.g, g.p);
 355     fail_2:
 356       G_DESTROYGROUP(g.g);
 357     fail_1:
 358       key_fetchdone(kp);
 359     fail_0:
 360       continue;
 361     }
 362
 363     T( trace(TRACE_CLIENT,
 364              "client: invalid or corrupt reply packet"); )
 365   }
 366
 367   die(1, "internal error: can't get here in check__ask");
 368   return (0);
 369 }
 370
 371 /* --- @check__client@ --- *
 372  *
 373  * Arguments:   @request *rq@ = pointer to a request block
 374  *              @FILE *fp@ = file containing server configuration
 375  *
 376  * Returns:     Nonzero if OK, zero if forbidden
 377  *
 378  * Use:         Asks one or several servers whether a request is acceptable.
 379  */
 380
 381 int check__client(request *rq, FILE *fp)
 382 {
 383   /* --- Format of the file --- *
 384    *
 385    * The `servers' file contains entries of the form
 386    *
 387    *    %%\syntax{<host> [`:' <port>]}%%
 388    *
 389    * separates by whitespace.  I build them all into an array of socket
 390    * addresses and pass the whole lot to another function.
 391    */
 392
 393   struct sockaddr_in *serv;             /* Array of servers */
 394   size_t n_serv, max_serv;              /* Number and maximum number */
 395
 396   /* --- Initialise the server array --- */
 397
 398   T( trace(TRACE_CLIENT, "client: reading server definitions"); )
 399   n_serv = 0; max_serv = 4;             /* Four seems reasonable */
 400   serv = xmalloc(sizeof(*serv) * max_serv);
 401
 402   /* --- Start reading the file --- */
 403
 404   {
 405     char buff[256], *p, *l;             /* A buffer and pointers for it */
 406     int port;                           /* Default port for servers */
 407     int state;                          /* Current parser state */
 408     struct in_addr t_host;              /* Temp place for an address*/
 409     int t_port;                         /* Temp place for a port */
 410     int ch;                             /* The current character */
 411
 412     /* --- Parser states --- */
 413
 414     enum {
 415       st_start,                         /* Waiting to begin */
 416       st_host,                          /* Reading a new hostname */
 417       st_colon,                         /* Expecting a colon, maybe */
 418       st_preport,                       /* Waiting before reading port */
 419       st_port,                          /* Reading a port number */
 420       st_commit,                        /* Commit a newly read server */
 421       st_done                           /* Finished reading the file */
 422     };
 423
 424     /* --- Find a default port --- */
 425
 426     {
 427       struct servent *s = getservbyname(quis(), "udp");
 428       port = (s ? s->s_port : htons(SERVER_PORT));
 429     }
 430
 431     /* --- Initialise for scanning the file --- */
 432
 433     state = st_host;
 434     p = buff;
 435     l = buff + sizeof(buff);
 436     t_port = port;
 437     ch = getc(fp);
 438
 439     /* --- Go for it --- */
 440
 441     while (state != st_done) {
 442       switch (state) {
 443
 444         /* --- Initial whitespace before hostname --- */
 445
 446         case st_start:
 447           if (ch == EOF)
 448             state = st_done;
 449           else if (isspace((unsigned char)ch))
 450             ch = getc(fp);
 451           else
 452             state = st_host;
 453           break;
 454
 455         /* --- Read a host name --- */
 456
 457         case st_host:
 458           if (p == l)
 459             die(1, "string too long in `" file_SERVER "'");
 460           if (ch != EOF && !isspace((unsigned char)ch) && ch != ':') {
 461             *p++ = ch;
 462             ch = getc(fp);
 463           } else {
 464             struct hostent *h;
 465
 466             *p++ = 0;
 467             if ((h = gethostbyname(buff)) == 0)
 468               die(1, "unknown host `%s' in `" file_SERVER "'", buff);
 469             memcpy(&t_host, h->h_addr, sizeof(t_host));
 470             state = st_colon;
 471           }
 472           break;
 473
 474         /* --- Waiting for a colon coming up --- */
 475
 476         case st_colon:
 477           if (ch == EOF)
 478             state = st_commit;
 479           else if (isspace((unsigned char)ch))
 480             ch = getc(fp);
 481           else if (ch == ':') {
 482             state = st_preport;
 483             ch = getc(fp);
 484           }
 485           else
 486             state = st_commit;
 487           break;
 488
 489         /* --- Clearing whitespace before a port number --- */
 490
 491         case st_preport:
 492           if (ch == EOF)
 493             state = st_commit;
 494           else if (isspace((unsigned char)ch))
 495             ch = getc(fp);
 496           else {
 497             state = st_port;
 498             p = buff;
 499           }
 500           break;
 501
 502         /* --- Read a port number --- */
 503
 504         case st_port:
 505           if (p == l)
 506             die(1, "string too long in `" file_SERVER "'");
 507           if (ch != EOF && !isspace((unsigned char)ch) && ch != ':') {
 508             *p++ = ch;
 509             ch = getc(fp);
 510           } else {
 511             struct servent *s;
 512
 513             *p++ = 0;
 514             s = getservbyname(buff, "udp");
 515             if (!s && isdigit((unsigned char)buff[0]))
 516               t_port = htons(atoi(buff));
 517             else if (!s)
 518               die(1, "unknown service `%s' in `" file_SERVER "'", buff);
 519             else
 520               t_port = s->s_port;
 521             state = st_commit;
 522           }
 523           break;
 524
 525         /* --- A server has been read successfully --- */
 526
 527         case st_commit:
 528           if (n_serv == max_serv) {
 529             max_serv *= 2;
 530             serv = xrealloc(serv, n_serv * sizeof(*serv),
 531                             max_serv * sizeof(*serv));
 532           }
 533           serv[n_serv].sin_family = AF_INET;
 534           serv[n_serv].sin_addr = t_host;
 535           serv[n_serv].sin_port = t_port;
 536           n_serv++;
 537           state = st_start;
 538           p = buff;
 539           t_port = port;
 540           break;
 541
 542         /* --- A safety net for a broken parser --- */
 543
 544         default:
 545           die(1, "internal error: can't get here in check__client");
 546           break;
 547       }
 548     }
 549   }
 550
 551   fclose(fp);
 552
 553   /* --- Now start sending requests --- */
 554
 555   if (!n_serv)
 556     die(1, "no servers specified in `" file_SERVER "'");
 557
 558   IF_TRACING(TRACE_CLIENT, {
 559     size_t i;
 560
 561     for (i = 0; i < n_serv; i++) {
 562       trace(TRACE_CLIENT, "client: server %s port %i",
 563             inet_ntoa(serv[i].sin_addr), ntohs(serv[i].sin_port));
 564     }
 565   })
 566   return (check__ask(rq, serv, n_serv));
 567 }
 568
 569 #endif
 570
 571 /*----- Main checking function --------------------------------------------*/
 572
 573 /* --- @check@ --- *
 574  *
 575  * Arguments:   @request *rq@ = pointer to request buffer
 576  *
 577  * Returns:     Nonzero if OK, zero if forbidden
 578  *
 579  * Use:         Checks to see if the request is acceptable.
 580  */
 581
 582 int check(request *rq)
 583 {
 584   FILE *fp;
 585
 586   /* --- Check if we need to talk to a server --- */
 587
 588 #ifndef NONETWORK
 589   if ((fp = fopen(file_SERVER, "r")) != 0)
 590     return (check__client(rq, fp));
 591 #endif
 592
 593   /* --- Otherwise do this all the old-fashioned way --- */
 594
 595   if ((fp = fopen(file_RULES, "r")) == 0) {
 596     die(1, "couldn't read configuration file `%s': %s",
 597         file_RULES, strerror(errno));
 598   }
 599
 600   userdb_init();
 601   userdb_local();
 602   userdb_yp();
 603   netg_init();
 604   name_init();
 605   rule_init();
 606   lexer_scan(fp);
 607   parse();
 608   fclose(fp);
 609
 610   return (rule_check(rq));
 611 }
 612
 613 /*----- That's all, folks -------------------------------------------------*/