ssh-agent.c

   1 /*      $OpenBSD: ssh-agent.c,v 1.28 2000/04/14 10:30:33 markus Exp $   */
   2
   3 /*
   4  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   5  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   6  *                    All rights reserved
   7  * Created: Wed Mar 29 03:46:59 1995 ylo
   8  * The authentication agent program.
   9  */
  10
  11 #include "includes.h"
  12 RCSID("$OpenBSD: ssh-agent.c,v 1.28 2000/04/14 10:30:33 markus Exp $");
  13
  14 #include "ssh.h"
  15 #include "rsa.h"
  16 #include "authfd.h"
  17 #include "buffer.h"
  18 #include "bufaux.h"
  19 #include "xmalloc.h"
  20 #include "packet.h"
  21 #include "getput.h"
  22 #include "mpaux.h"
  23
  24 #include <openssl/md5.h>
  25
  26 typedef struct {
  27         int fd;
  28         enum {
  29                 AUTH_UNUSED, AUTH_SOCKET, AUTH_CONNECTION
  30         } type;
  31         Buffer input;
  32         Buffer output;
  33 } SocketEntry;
  34
  35 unsigned int sockets_alloc = 0;
  36 SocketEntry *sockets = NULL;
  37
  38 typedef struct {
  39         RSA *key;
  40         char *comment;
  41 } Identity;
  42
  43 unsigned int num_identities = 0;
  44 Identity *identities = NULL;
  45
  46 int max_fd = 0;
  47
  48 /* pid of shell == parent of agent */
  49 int parent_pid = -1;
  50
  51 /* pathname and directory for AUTH_SOCKET */
  52 char socket_name[1024];
  53 char socket_dir[1024];
  54
  55 #ifdef HAVE___PROGNAME
  56 extern char *__progname;
  57 #else /* HAVE___PROGNAME */
  58 const char *__progname = "ssh-agent";
  59 #endif /* HAVE___PROGNAME */
  60
  61 void
  62 process_request_identity(SocketEntry *e)
  63 {
  64         Buffer msg;
  65         int i;
  66
  67         buffer_init(&msg);
  68         buffer_put_char(&msg, SSH_AGENT_RSA_IDENTITIES_ANSWER);
  69         buffer_put_int(&msg, num_identities);
  70         for (i = 0; i < num_identities; i++) {
  71                 buffer_put_int(&msg, BN_num_bits(identities[i].key->n));
  72                 buffer_put_bignum(&msg, identities[i].key->e);
  73                 buffer_put_bignum(&msg, identities[i].key->n);
  74                 buffer_put_string(&msg, identities[i].comment,
  75                                   strlen(identities[i].comment));
  76         }
  77         buffer_put_int(&e->output, buffer_len(&msg));
  78         buffer_append(&e->output, buffer_ptr(&msg), buffer_len(&msg));
  79         buffer_free(&msg);
  80 }
  81
  82 void
  83 process_authentication_challenge(SocketEntry *e)
  84 {
  85         int i, pub_bits, len;
  86         BIGNUM *pub_e, *pub_n, *challenge;
  87         Buffer msg;
  88         MD5_CTX md;
  89         unsigned char buf[32], mdbuf[16], session_id[16];
  90         unsigned int response_type;
  91
  92         buffer_init(&msg);
  93         pub_e = BN_new();
  94         pub_n = BN_new();
  95         challenge = BN_new();
  96         pub_bits = buffer_get_int(&e->input);
  97         buffer_get_bignum(&e->input, pub_e);
  98         buffer_get_bignum(&e->input, pub_n);
  99         buffer_get_bignum(&e->input, challenge);
 100         if (buffer_len(&e->input) == 0) {
 101                 /* Compatibility code for old servers. */
 102                 memset(session_id, 0, 16);
 103                 response_type = 0;
 104         } else {
 105                 /* New code. */
 106                 buffer_get(&e->input, (char *) session_id, 16);
 107                 response_type = buffer_get_int(&e->input);
 108         }
 109         for (i = 0; i < num_identities; i++)
 110                 if (pub_bits == BN_num_bits(identities[i].key->n) &&
 111                     BN_cmp(pub_e, identities[i].key->e) == 0 &&
 112                     BN_cmp(pub_n, identities[i].key->n) == 0) {
 113                         /* Decrypt the challenge using the private key. */
 114                         rsa_private_decrypt(challenge, challenge, identities[i].key);
 115
 116                         /* Compute the desired response. */
 117                         switch (response_type) {
 118                         case 0:/* As of protocol 1.0 */
 119                                 /* This response type is no longer supported. */
 120                                 log("Compatibility with ssh protocol 1.0 no longer supported.");
 121                                 buffer_put_char(&msg, SSH_AGENT_FAILURE);
 122                                 goto send;
 123
 124                         case 1:/* As of protocol 1.1 */
 125                                 /* The response is MD5 of decrypted challenge plus session id. */
 126                                 len = BN_num_bytes(challenge);
 127
 128                                 if (len <= 0 || len > 32) {
 129                                         fatal("process_authentication_challenge: "
 130                                          "bad challenge length %d", len);
 131                                 }
 132                                 memset(buf, 0, 32);
 133                                 BN_bn2bin(challenge, buf + 32 - len);
 134                                 MD5_Init(&md);
 135                                 MD5_Update(&md, buf, 32);
 136                                 MD5_Update(&md, session_id, 16);
 137                                 MD5_Final(mdbuf, &md);
 138                                 break;
 139
 140                         default:
 141                                 fatal("process_authentication_challenge: bad response_type %d",
 142                                       response_type);
 143                                 break;
 144                         }
 145
 146                         /* Send the response. */
 147                         buffer_put_char(&msg, SSH_AGENT_RSA_RESPONSE);
 148                         for (i = 0; i < 16; i++)
 149                                 buffer_put_char(&msg, mdbuf[i]);
 150
 151                         goto send;
 152                 }
 153         /* Unknown identity.  Send failure. */
 154         buffer_put_char(&msg, SSH_AGENT_FAILURE);
 155 send:
 156         buffer_put_int(&e->output, buffer_len(&msg));
 157         buffer_append(&e->output, buffer_ptr(&msg),
 158                       buffer_len(&msg));
 159         buffer_free(&msg);
 160         BN_clear_free(pub_e);
 161         BN_clear_free(pub_n);
 162         BN_clear_free(challenge);
 163 }
 164
 165 void
 166 process_remove_identity(SocketEntry *e)
 167 {
 168         unsigned int bits;
 169         unsigned int i;
 170         BIGNUM *dummy, *n;
 171
 172         dummy = BN_new();
 173         n = BN_new();
 174
 175         /* Get the key from the packet. */
 176         bits = buffer_get_int(&e->input);
 177         buffer_get_bignum(&e->input, dummy);
 178         buffer_get_bignum(&e->input, n);
 179
 180         if (bits != BN_num_bits(n))
 181                 error("Warning: identity keysize mismatch: actual %d, announced %d",
 182                       BN_num_bits(n), bits);
 183
 184         /* Check if we have the key. */
 185         for (i = 0; i < num_identities; i++)
 186                 if (BN_cmp(identities[i].key->n, n) == 0) {
 187                         /*
 188                          * We have this key.  Free the old key.  Since we
 189                          * don\'t want to leave empty slots in the middle of
 190                          * the array, we actually free the key there and copy
 191                          * data from the last entry.
 192                          */
 193                         RSA_free(identities[i].key);
 194                         xfree(identities[i].comment);
 195                         if (i < num_identities - 1)
 196                                 identities[i] = identities[num_identities - 1];
 197                         num_identities--;
 198                         BN_clear_free(dummy);
 199                         BN_clear_free(n);
 200
 201                         /* Send success. */
 202                         buffer_put_int(&e->output, 1);
 203                         buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 204                         return;
 205                 }
 206         /* We did not have the key. */
 207         BN_clear(dummy);
 208         BN_clear(n);
 209
 210         /* Send failure. */
 211         buffer_put_int(&e->output, 1);
 212         buffer_put_char(&e->output, SSH_AGENT_FAILURE);
 213 }
 214
 215 /*
 216  * Removes all identities from the agent.
 217  */
 218 void
 219 process_remove_all_identities(SocketEntry *e)
 220 {
 221         unsigned int i;
 222
 223         /* Loop over all identities and clear the keys. */
 224         for (i = 0; i < num_identities; i++) {
 225                 RSA_free(identities[i].key);
 226                 xfree(identities[i].comment);
 227         }
 228
 229         /* Mark that there are no identities. */
 230         num_identities = 0;
 231
 232         /* Send success. */
 233         buffer_put_int(&e->output, 1);
 234         buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 235         return;
 236 }
 237
 238 /*
 239  * Adds an identity to the agent.
 240  */
 241 void
 242 process_add_identity(SocketEntry *e)
 243 {
 244         RSA *k;
 245         int i;
 246         BIGNUM *aux;
 247         BN_CTX *ctx;
 248
 249         if (num_identities == 0)
 250                 identities = xmalloc(sizeof(Identity));
 251         else
 252                 identities = xrealloc(identities, (num_identities + 1) * sizeof(Identity));
 253
 254         identities[num_identities].key = RSA_new();
 255         k = identities[num_identities].key;
 256         buffer_get_int(&e->input);      /* bits */
 257         k->n = BN_new();
 258         buffer_get_bignum(&e->input, k->n);
 259         k->e = BN_new();
 260         buffer_get_bignum(&e->input, k->e);
 261         k->d = BN_new();
 262         buffer_get_bignum(&e->input, k->d);
 263         k->iqmp = BN_new();
 264         buffer_get_bignum(&e->input, k->iqmp);
 265         /* SSH and SSL have p and q swapped */
 266         k->q = BN_new();
 267         buffer_get_bignum(&e->input, k->q);     /* p */
 268         k->p = BN_new();
 269         buffer_get_bignum(&e->input, k->p);     /* q */
 270
 271         /* Generate additional parameters */
 272         aux = BN_new();
 273         ctx = BN_CTX_new();
 274
 275         BN_sub(aux, k->q, BN_value_one());
 276         k->dmq1 = BN_new();
 277         BN_mod(k->dmq1, k->d, aux, ctx);
 278
 279         BN_sub(aux, k->p, BN_value_one());
 280         k->dmp1 = BN_new();
 281         BN_mod(k->dmp1, k->d, aux, ctx);
 282
 283         BN_clear_free(aux);
 284         BN_CTX_free(ctx);
 285
 286         identities[num_identities].comment = buffer_get_string(&e->input, NULL);
 287
 288         /* Check if we already have the key. */
 289         for (i = 0; i < num_identities; i++)
 290                 if (BN_cmp(identities[i].key->n, k->n) == 0) {
 291                         /*
 292                          * We already have this key.  Clear and free the new
 293                          * data and return success.
 294                          */
 295                         RSA_free(k);
 296                         xfree(identities[num_identities].comment);
 297
 298                         /* Send success. */
 299                         buffer_put_int(&e->output, 1);
 300                         buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 301                         return;
 302                 }
 303         /* Increment the number of identities. */
 304         num_identities++;
 305
 306         /* Send a success message. */
 307         buffer_put_int(&e->output, 1);
 308         buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 309 }
 310
 311 void
 312 process_message(SocketEntry *e)
 313 {
 314         unsigned int msg_len;
 315         unsigned int type;
 316         unsigned char *cp;
 317         if (buffer_len(&e->input) < 5)
 318                 return;         /* Incomplete message. */
 319         cp = (unsigned char *) buffer_ptr(&e->input);
 320         msg_len = GET_32BIT(cp);
 321         if (msg_len > 256 * 1024) {
 322                 shutdown(e->fd, SHUT_RDWR);
 323                 close(e->fd);
 324                 e->type = AUTH_UNUSED;
 325                 return;
 326         }
 327         if (buffer_len(&e->input) < msg_len + 4)
 328                 return;
 329         buffer_consume(&e->input, 4);
 330         type = buffer_get_char(&e->input);
 331
 332         switch (type) {
 333         case SSH_AGENTC_REQUEST_RSA_IDENTITIES:
 334                 process_request_identity(e);
 335                 break;
 336         case SSH_AGENTC_RSA_CHALLENGE:
 337                 process_authentication_challenge(e);
 338                 break;
 339         case SSH_AGENTC_ADD_RSA_IDENTITY:
 340                 process_add_identity(e);
 341                 break;
 342         case SSH_AGENTC_REMOVE_RSA_IDENTITY:
 343                 process_remove_identity(e);
 344                 break;
 345         case SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
 346                 process_remove_all_identities(e);
 347                 break;
 348         default:
 349                 /* Unknown message.  Respond with failure. */
 350                 error("Unknown message %d", type);
 351                 buffer_clear(&e->input);
 352                 buffer_put_int(&e->output, 1);
 353                 buffer_put_char(&e->output, SSH_AGENT_FAILURE);
 354                 break;
 355         }
 356 }
 357
 358 void
 359 new_socket(int type, int fd)
 360 {
 361         unsigned int i, old_alloc;
 362         if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0)
 363                 error("fcntl O_NONBLOCK: %s", strerror(errno));
 364
 365         if (fd > max_fd)
 366                 max_fd = fd;
 367
 368         for (i = 0; i < sockets_alloc; i++)
 369                 if (sockets[i].type == AUTH_UNUSED) {
 370                         sockets[i].fd = fd;
 371                         sockets[i].type = type;
 372                         buffer_init(&sockets[i].input);
 373                         buffer_init(&sockets[i].output);
 374                         return;
 375                 }
 376         old_alloc = sockets_alloc;
 377         sockets_alloc += 10;
 378         if (sockets)
 379                 sockets = xrealloc(sockets, sockets_alloc * sizeof(sockets[0]));
 380         else
 381                 sockets = xmalloc(sockets_alloc * sizeof(sockets[0]));
 382         for (i = old_alloc; i < sockets_alloc; i++)
 383                 sockets[i].type = AUTH_UNUSED;
 384         sockets[old_alloc].type = type;
 385         sockets[old_alloc].fd = fd;
 386         buffer_init(&sockets[old_alloc].input);
 387         buffer_init(&sockets[old_alloc].output);
 388 }
 389
 390 void
 391 prepare_select(fd_set *readset, fd_set *writeset)
 392 {
 393         unsigned int i;
 394         for (i = 0; i < sockets_alloc; i++)
 395                 switch (sockets[i].type) {
 396                 case AUTH_SOCKET:
 397                 case AUTH_CONNECTION:
 398                         FD_SET(sockets[i].fd, readset);
 399                         if (buffer_len(&sockets[i].output) > 0)
 400                                 FD_SET(sockets[i].fd, writeset);
 401                         break;
 402                 case AUTH_UNUSED:
 403                         break;
 404                 default:
 405                         fatal("Unknown socket type %d", sockets[i].type);
 406                         break;
 407                 }
 408 }
 409
 410 void
 411 after_select(fd_set *readset, fd_set *writeset)
 412 {
 413         unsigned int i;
 414         int len, sock;
 415         socklen_t slen;
 416         char buf[1024];
 417         struct sockaddr_un sunaddr;
 418
 419         for (i = 0; i < sockets_alloc; i++)
 420                 switch (sockets[i].type) {
 421                 case AUTH_UNUSED:
 422                         break;
 423                 case AUTH_SOCKET:
 424                         if (FD_ISSET(sockets[i].fd, readset)) {
 425                                 slen = sizeof(sunaddr);
 426                                 sock = accept(sockets[i].fd, (struct sockaddr *) & sunaddr, &slen);
 427                                 if (sock < 0) {
 428                                         perror("accept from AUTH_SOCKET");
 429                                         break;
 430                                 }
 431                                 new_socket(AUTH_CONNECTION, sock);
 432                         }
 433                         break;
 434                 case AUTH_CONNECTION:
 435                         if (buffer_len(&sockets[i].output) > 0 &&
 436                             FD_ISSET(sockets[i].fd, writeset)) {
 437                                 len = write(sockets[i].fd, buffer_ptr(&sockets[i].output),
 438                                          buffer_len(&sockets[i].output));
 439                                 if (len <= 0) {
 440                                         shutdown(sockets[i].fd, SHUT_RDWR);
 441                                         close(sockets[i].fd);
 442                                         sockets[i].type = AUTH_UNUSED;
 443                                         break;
 444                                 }
 445                                 buffer_consume(&sockets[i].output, len);
 446                         }
 447                         if (FD_ISSET(sockets[i].fd, readset)) {
 448                                 len = read(sockets[i].fd, buf, sizeof(buf));
 449                                 if (len <= 0) {
 450                                         shutdown(sockets[i].fd, SHUT_RDWR);
 451                                         close(sockets[i].fd);
 452                                         sockets[i].type = AUTH_UNUSED;
 453                                         break;
 454                                 }
 455                                 buffer_append(&sockets[i].input, buf, len);
 456                                 process_message(&sockets[i]);
 457                         }
 458                         break;
 459                 default:
 460                         fatal("Unknown type %d", sockets[i].type);
 461                 }
 462 }
 463
 464 void
 465 check_parent_exists(int sig)
 466 {
 467         if (kill(parent_pid, 0) < 0) {
 468                 /* printf("Parent has died - Authentication agent exiting.\n"); */
 469                 exit(1);
 470         }
 471         signal(SIGALRM, check_parent_exists);
 472         alarm(10);
 473 }
 474
 475 void
 476 cleanup_socket(void)
 477 {
 478         remove(socket_name);
 479         rmdir(socket_dir);
 480 }
 481
 482 void
 483 cleanup_exit(int i)
 484 {
 485         cleanup_socket();
 486         exit(i);
 487 }
 488
 489 void
 490 usage()
 491 {
 492         fprintf(stderr, "ssh-agent version %s\n", SSH_VERSION);
 493         fprintf(stderr, "Usage: %s [-c | -s] [-k] [command {args...]]\n",
 494                 __progname);
 495         exit(1);
 496 }
 497
 498 int
 499 main(int ac, char **av)
 500 {
 501         fd_set readset, writeset;
 502         int sock, c_flag = 0, k_flag = 0, s_flag = 0, ch;
 503         struct sockaddr_un sunaddr;
 504         pid_t pid;
 505         char *shell, *format, *pidstr, pidstrbuf[1 + 3 * sizeof pid];
 506
 507         /* check if RSA support exists */
 508         if (rsa_alive() == 0) {
 509                 fprintf(stderr,
 510                         "%s: no RSA support in libssl and libcrypto.  See ssl(8).\n",
 511                         __progname);
 512                 exit(1);
 513         }
 514         while ((ch = getopt(ac, av, "cks")) != -1) {
 515                 switch (ch) {
 516                 case 'c':
 517                         if (s_flag)
 518                                 usage();
 519                         c_flag++;
 520                         break;
 521                 case 'k':
 522                         k_flag++;
 523                         break;
 524                 case 's':
 525                         if (c_flag)
 526                                 usage();
 527                         s_flag++;
 528                         break;
 529                 default:
 530                         usage();
 531                 }
 532         }
 533         ac -= optind;
 534         av += optind;
 535
 536         if (ac > 0 && (c_flag || k_flag || s_flag))
 537                 usage();
 538
 539         if (ac == 0 && !c_flag && !k_flag && !s_flag) {
 540                 shell = getenv("SHELL");
 541                 if (shell != NULL && strncmp(shell + strlen(shell) - 3, "csh", 3) == 0)
 542                         c_flag = 1;
 543         }
 544         if (k_flag) {
 545                 pidstr = getenv(SSH_AGENTPID_ENV_NAME);
 546                 if (pidstr == NULL) {
 547                         fprintf(stderr, "%s not set, cannot kill agent\n",
 548                                 SSH_AGENTPID_ENV_NAME);
 549                         exit(1);
 550                 }
 551                 pid = atoi(pidstr);
 552                 if (pid < 1) {  /* XXX PID_MAX check too */
 553                         fprintf(stderr, "%s=\"%s\", which is not a good PID\n",
 554                                 SSH_AGENTPID_ENV_NAME, pidstr);
 555                         exit(1);
 556                 }
 557                 if (kill(pid, SIGTERM) == -1) {
 558                         perror("kill");
 559                         exit(1);
 560                 }
 561                 format = c_flag ? "unsetenv %s;\n" : "unset %s;\n";
 562                 printf(format, SSH_AUTHSOCKET_ENV_NAME);
 563                 printf(format, SSH_AGENTPID_ENV_NAME);
 564                 printf("echo Agent pid %d killed;\n", pid);
 565                 exit(0);
 566         }
 567         parent_pid = getpid();
 568
 569         /* Create private directory for agent socket */
 570         strlcpy(socket_dir, "/tmp/ssh-XXXXXXXX", sizeof socket_dir);
 571         if (mkdtemp(socket_dir) == NULL) {
 572                 perror("mkdtemp: private socket dir");
 573                 exit(1);
 574         }
 575         snprintf(socket_name, sizeof socket_name, "%s/agent.%d", socket_dir,
 576                  parent_pid);
 577
 578         /*
 579          * Create socket early so it will exist before command gets run from
 580          * the parent.
 581          */
 582         sock = socket(AF_UNIX, SOCK_STREAM, 0);
 583         if (sock < 0) {
 584                 perror("socket");
 585                 cleanup_exit(1);
 586         }
 587         memset(&sunaddr, 0, sizeof(sunaddr));
 588         sunaddr.sun_family = AF_UNIX;
 589         strlcpy(sunaddr.sun_path, socket_name, sizeof(sunaddr.sun_path));
 590         if (bind(sock, (struct sockaddr *) & sunaddr, sizeof(sunaddr)) < 0) {
 591                 perror("bind");
 592                 cleanup_exit(1);
 593         }
 594         if (listen(sock, 5) < 0) {
 595                 perror("listen");
 596                 cleanup_exit(1);
 597         }
 598         /*
 599          * Fork, and have the parent execute the command, if any, or present
 600          * the socket data.  The child continues as the authentication agent.
 601          */
 602         pid = fork();
 603         if (pid == -1) {
 604                 perror("fork");
 605                 exit(1);
 606         }
 607         if (pid != 0) {         /* Parent - execute the given command. */
 608                 close(sock);
 609                 snprintf(pidstrbuf, sizeof pidstrbuf, "%d", pid);
 610                 if (ac == 0) {
 611                         format = c_flag ? "setenv %s %s;\n" : "%s=%s; export %s;\n";
 612                         printf(format, SSH_AUTHSOCKET_ENV_NAME, socket_name,
 613                                SSH_AUTHSOCKET_ENV_NAME);
 614                         printf(format, SSH_AGENTPID_ENV_NAME, pidstrbuf,
 615                                SSH_AGENTPID_ENV_NAME);
 616                         printf("echo Agent pid %d;\n", pid);
 617                         exit(0);
 618                 }
 619                 setenv(SSH_AUTHSOCKET_ENV_NAME, socket_name, 1);
 620                 setenv(SSH_AGENTPID_ENV_NAME, pidstrbuf, 1);
 621                 execvp(av[0], av);
 622                 perror(av[0]);
 623                 exit(1);
 624         }
 625         close(0);
 626         close(1);
 627         close(2);
 628
 629         if (setsid() == -1) {
 630                 perror("setsid");
 631                 cleanup_exit(1);
 632         }
 633         if (atexit(cleanup_socket) < 0) {
 634                 perror("atexit");
 635                 cleanup_exit(1);
 636         }
 637         new_socket(AUTH_SOCKET, sock);
 638         if (ac > 0) {
 639                 signal(SIGALRM, check_parent_exists);
 640                 alarm(10);
 641         }
 642         signal(SIGINT, SIG_IGN);
 643         signal(SIGPIPE, SIG_IGN);
 644         signal(SIGHUP, cleanup_exit);
 645         signal(SIGTERM, cleanup_exit);
 646         while (1) {
 647                 FD_ZERO(&readset);
 648                 FD_ZERO(&writeset);
 649                 prepare_select(&readset, &writeset);
 650                 if (select(max_fd + 1, &readset, &writeset, NULL, NULL) < 0) {
 651                         if (errno == EINTR)
 652                                 continue;
 653                         exit(1);
 654                 }
 655                 after_select(&readset, &writeset);
 656         }
 657         /* NOTREACHED */
 658 }