1 /* $OpenBSD: authfd.c,v 1.127 2021/01/26 00:46:17 djm Exp $ */ 2 /* 3 * Author: Tatu Ylonen <ylo@cs.hut.fi> 4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 5 * All rights reserved 6 * Functions for connecting the local authentication agent. 7 * 8 * As far as I am concerned, the code I have written for this software 9 * can be used freely for any purpose. Any derived versions of this 10 * software must be clearly marked as such, and if the derived work is 11 * incompatible with the protocol description in the RFC file, it must be 12 * called by a name other than "ssh" or "Secure Shell". 13 * 14 * SSH2 implementation, 15 * Copyright (c) 2000 Markus Friedl. All rights reserved. 16 * 17 * Redistribution and use in source and binary forms, with or without 18 * modification, are permitted provided that the following conditions 19 * are met: 20 * 1. Redistributions of source code must retain the above copyright 21 * notice, this list of conditions and the following disclaimer. 22 * 2. Redistributions in binary form must reproduce the above copyright 23 * notice, this list of conditions and the following disclaimer in the 24 * documentation and/or other materials provided with the distribution. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 27 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 28 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 29 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 30 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 31 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 35 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 36 */ 37 38 #include "includes.h" 39 40 #include <sys/types.h> 41 #include <sys/un.h> 42 #include <sys/socket.h> 43 44 #include <fcntl.h> 45 #include <stdlib.h> 46 #include <signal.h> 47 #include <string.h> 48 #include <stdarg.h> 49 #include <unistd.h> 50 #include <errno.h> 51 52 #include "xmalloc.h" 53 #include "ssh.h" 54 #include "sshbuf.h" 55 #include "sshkey.h" 56 #include "authfd.h" 57 #include "cipher.h" 58 #include "compat.h" 59 #include "log.h" 60 #include "atomicio.h" 61 #include "misc.h" 62 #include "ssherr.h" 63 64 #define MAX_AGENT_IDENTITIES 2048 /* Max keys in agent reply */ 65 #define MAX_AGENT_REPLY_LEN (256 * 1024) /* Max bytes in agent reply */ 66 67 /* macro to check for "agent failure" message */ 68 #define agent_failed(x) \ 69 ((x == SSH_AGENT_FAILURE) || \ 70 (x == SSH_COM_AGENT2_FAILURE) || \ 71 (x == SSH2_AGENT_FAILURE)) 72 73 /* Convert success/failure response from agent to a err.h status */ 74 static int 75 decode_reply(u_char type) 76 { 77 if (agent_failed(type)) 78 return SSH_ERR_AGENT_FAILURE; 79 else if (type == SSH_AGENT_SUCCESS) 80 return 0; 81 else 82 return SSH_ERR_INVALID_FORMAT; 83 } 84 85 /* 86 * Opens an authentication socket at the provided path and stores the file 87 * descriptor in fdp. Returns 0 on success and an error on failure. 88 */ 89 int 90 ssh_get_authentication_socket_path(const char *authsocket, int *fdp) 91 { 92 int sock, oerrno; 93 struct sockaddr_un sunaddr; 94 95 memset(&sunaddr, 0, sizeof(sunaddr)); 96 sunaddr.sun_family = AF_UNIX; 97 strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path)); 98 99 if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) 100 return SSH_ERR_SYSTEM_ERROR; 101 102 /* close on exec */ 103 if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 || 104 connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) == -1) { 105 oerrno = errno; 106 close(sock); 107 errno = oerrno; 108 return SSH_ERR_SYSTEM_ERROR; 109 } 110 if (fdp != NULL) 111 *fdp = sock; 112 else 113 close(sock); 114 return 0; 115 } 116 117 /* 118 * Opens the default authentication socket and stores the file descriptor in 119 * fdp. Returns 0 on success and an error on failure. 120 */ 121 int 122 ssh_get_authentication_socket(int *fdp) 123 { 124 const char *authsocket; 125 126 if (fdp != NULL) 127 *fdp = -1; 128 129 authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME); 130 if (authsocket == NULL || *authsocket == '\0') 131 return SSH_ERR_AGENT_NOT_PRESENT; 132 133 return ssh_get_authentication_socket_path(authsocket, fdp); 134 } 135 136 /* Communicate with agent: send request and read reply */ 137 static int 138 ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply) 139 { 140 int r; 141 size_t l, len; 142 char buf[1024]; 143 144 /* Get the length of the message, and format it in the buffer. */ 145 len = sshbuf_len(request); 146 POKE_U32(buf, len); 147 148 /* Send the length and then the packet to the agent. */ 149 if (atomicio(vwrite, sock, buf, 4) != 4 || 150 atomicio(vwrite, sock, sshbuf_mutable_ptr(request), 151 sshbuf_len(request)) != sshbuf_len(request)) 152 return SSH_ERR_AGENT_COMMUNICATION; 153 /* 154 * Wait for response from the agent. First read the length of the 155 * response packet. 156 */ 157 if (atomicio(read, sock, buf, 4) != 4) 158 return SSH_ERR_AGENT_COMMUNICATION; 159 160 /* Extract the length, and check it for sanity. */ 161 len = PEEK_U32(buf); 162 if (len > MAX_AGENT_REPLY_LEN) 163 return SSH_ERR_INVALID_FORMAT; 164 165 /* Read the rest of the response in to the buffer. */ 166 sshbuf_reset(reply); 167 while (len > 0) { 168 l = len; 169 if (l > sizeof(buf)) 170 l = sizeof(buf); 171 if (atomicio(read, sock, buf, l) != l) 172 return SSH_ERR_AGENT_COMMUNICATION; 173 if ((r = sshbuf_put(reply, buf, l)) != 0) 174 return r; 175 len -= l; 176 } 177 return 0; 178 } 179 180 /* Communicate with agent: sent request, read and decode status reply */ 181 static int 182 ssh_request_reply_decode(int sock, struct sshbuf *request) 183 { 184 struct sshbuf *reply; 185 int r; 186 u_char type; 187 188 if ((reply = sshbuf_new()) == NULL) 189 return SSH_ERR_ALLOC_FAIL; 190 if ((r = ssh_request_reply(sock, request, reply)) != 0 || 191 (r = sshbuf_get_u8(reply, &type)) != 0 || 192 (r = decode_reply(type)) != 0) 193 goto out; 194 /* success */ 195 r = 0; 196 out: 197 sshbuf_free(reply); 198 return r; 199 } 200 201 /* 202 * Closes the agent socket if it should be closed (depends on how it was 203 * obtained). The argument must have been returned by 204 * ssh_get_authentication_socket(). 205 */ 206 void 207 ssh_close_authentication_socket(int sock) 208 { 209 if (getenv(SSH_AUTHSOCKET_ENV_NAME)) 210 close(sock); 211 } 212 213 /* Lock/unlock agent */ 214 int 215 ssh_lock_agent(int sock, int lock, const char *password) 216 { 217 int r; 218 u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK; 219 struct sshbuf *msg; 220 221 if ((msg = sshbuf_new()) == NULL) 222 return SSH_ERR_ALLOC_FAIL; 223 if ((r = sshbuf_put_u8(msg, type)) != 0 || 224 (r = sshbuf_put_cstring(msg, password)) != 0 || 225 (r = ssh_request_reply_decode(sock, msg)) != 0) 226 goto out; 227 /* success */ 228 r = 0; 229 out: 230 sshbuf_free(msg); 231 return r; 232 } 233 234 235 static int 236 deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp) 237 { 238 int r; 239 char *comment = NULL; 240 const u_char *blob; 241 size_t blen; 242 243 if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 || 244 (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0) 245 goto out; 246 if ((r = sshkey_from_blob(blob, blen, keyp)) != 0) 247 goto out; 248 if (commentp != NULL) { 249 *commentp = comment; 250 comment = NULL; 251 } 252 r = 0; 253 out: 254 free(comment); 255 return r; 256 } 257 258 /* 259 * Fetch list of identities held by the agent. 260 */ 261 int 262 ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp) 263 { 264 u_char type; 265 u_int32_t num, i; 266 struct sshbuf *msg; 267 struct ssh_identitylist *idl = NULL; 268 int r; 269 270 /* 271 * Send a message to the agent requesting for a list of the 272 * identities it can represent. 273 */ 274 if ((msg = sshbuf_new()) == NULL) 275 return SSH_ERR_ALLOC_FAIL; 276 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0) 277 goto out; 278 279 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 280 goto out; 281 282 /* Get message type, and verify that we got a proper answer. */ 283 if ((r = sshbuf_get_u8(msg, &type)) != 0) 284 goto out; 285 if (agent_failed(type)) { 286 r = SSH_ERR_AGENT_FAILURE; 287 goto out; 288 } else if (type != SSH2_AGENT_IDENTITIES_ANSWER) { 289 r = SSH_ERR_INVALID_FORMAT; 290 goto out; 291 } 292 293 /* Get the number of entries in the response and check it for sanity. */ 294 if ((r = sshbuf_get_u32(msg, &num)) != 0) 295 goto out; 296 if (num > MAX_AGENT_IDENTITIES) { 297 r = SSH_ERR_INVALID_FORMAT; 298 goto out; 299 } 300 if (num == 0) { 301 r = SSH_ERR_AGENT_NO_IDENTITIES; 302 goto out; 303 } 304 305 /* Deserialise the response into a list of keys/comments */ 306 if ((idl = calloc(1, sizeof(*idl))) == NULL || 307 (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL || 308 (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) { 309 r = SSH_ERR_ALLOC_FAIL; 310 goto out; 311 } 312 for (i = 0; i < num;) { 313 if ((r = deserialise_identity2(msg, &(idl->keys[i]), 314 &(idl->comments[i]))) != 0) { 315 if (r == SSH_ERR_KEY_TYPE_UNKNOWN) { 316 /* Gracefully skip unknown key types */ 317 num--; 318 continue; 319 } else 320 goto out; 321 } 322 i++; 323 } 324 idl->nkeys = num; 325 *idlp = idl; 326 idl = NULL; 327 r = 0; 328 out: 329 sshbuf_free(msg); 330 if (idl != NULL) 331 ssh_free_identitylist(idl); 332 return r; 333 } 334 335 void 336 ssh_free_identitylist(struct ssh_identitylist *idl) 337 { 338 size_t i; 339 340 if (idl == NULL) 341 return; 342 for (i = 0; i < idl->nkeys; i++) { 343 if (idl->keys != NULL) 344 sshkey_free(idl->keys[i]); 345 if (idl->comments != NULL) 346 free(idl->comments[i]); 347 } 348 free(idl->keys); 349 free(idl->comments); 350 free(idl); 351 } 352 353 /* 354 * Check if the ssh agent has a given key. 355 * Returns 0 if found, or a negative SSH_ERR_* error code on failure. 356 */ 357 int 358 ssh_agent_has_key(int sock, const struct sshkey *key) 359 { 360 int r, ret = SSH_ERR_KEY_NOT_FOUND; 361 size_t i; 362 struct ssh_identitylist *idlist = NULL; 363 364 if ((r = ssh_fetch_identitylist(sock, &idlist)) != 0) { 365 return r; 366 } 367 368 for (i = 0; i < idlist->nkeys; i++) { 369 if (sshkey_equal_public(idlist->keys[i], key)) { 370 ret = 0; 371 break; 372 } 373 } 374 375 ssh_free_identitylist(idlist); 376 return ret; 377 } 378 379 /* 380 * Sends a challenge (typically from a server via ssh(1)) to the agent, 381 * and waits for a response from the agent. 382 * Returns true (non-zero) if the agent gave the correct answer, zero 383 * otherwise. 384 */ 385 386 387 /* encode signature algorithm in flag bits, so we can keep the msg format */ 388 static u_int 389 agent_encode_alg(const struct sshkey *key, const char *alg) 390 { 391 if (alg != NULL && sshkey_type_plain(key->type) == KEY_RSA) { 392 if (strcmp(alg, "rsa-sha2-256") == 0 || 393 strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0) 394 return SSH_AGENT_RSA_SHA2_256; 395 if (strcmp(alg, "rsa-sha2-512") == 0 || 396 strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0) 397 return SSH_AGENT_RSA_SHA2_512; 398 } 399 return 0; 400 } 401 402 /* ask agent to sign data, returns err.h code on error, 0 on success */ 403 int 404 ssh_agent_sign(int sock, const struct sshkey *key, 405 u_char **sigp, size_t *lenp, 406 const u_char *data, size_t datalen, const char *alg, u_int compat) 407 { 408 struct sshbuf *msg; 409 u_char *sig = NULL, type = 0; 410 size_t len = 0; 411 u_int flags = 0; 412 int r = SSH_ERR_INTERNAL_ERROR; 413 414 *sigp = NULL; 415 *lenp = 0; 416 417 if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE) 418 return SSH_ERR_INVALID_ARGUMENT; 419 if ((msg = sshbuf_new()) == NULL) 420 return SSH_ERR_ALLOC_FAIL; 421 flags |= agent_encode_alg(key, alg); 422 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 || 423 (r = sshkey_puts(key, msg)) != 0 || 424 (r = sshbuf_put_string(msg, data, datalen)) != 0 || 425 (r = sshbuf_put_u32(msg, flags)) != 0) 426 goto out; 427 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 428 goto out; 429 if ((r = sshbuf_get_u8(msg, &type)) != 0) 430 goto out; 431 if (agent_failed(type)) { 432 r = SSH_ERR_AGENT_FAILURE; 433 goto out; 434 } else if (type != SSH2_AGENT_SIGN_RESPONSE) { 435 r = SSH_ERR_INVALID_FORMAT; 436 goto out; 437 } 438 if ((r = sshbuf_get_string(msg, &sig, &len)) != 0) 439 goto out; 440 /* Check what we actually got back from the agent. */ 441 if ((r = sshkey_check_sigtype(sig, len, alg)) != 0) 442 goto out; 443 /* success */ 444 *sigp = sig; 445 *lenp = len; 446 sig = NULL; 447 len = 0; 448 r = 0; 449 out: 450 freezero(sig, len); 451 sshbuf_free(msg); 452 return r; 453 } 454 455 /* Encode key for a message to the agent. */ 456 457 458 static int 459 encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign, 460 const char *provider) 461 { 462 int r; 463 464 if (life != 0) { 465 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 || 466 (r = sshbuf_put_u32(m, life)) != 0) 467 goto out; 468 } 469 if (confirm != 0) { 470 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0) 471 goto out; 472 } 473 if (maxsign != 0) { 474 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 || 475 (r = sshbuf_put_u32(m, maxsign)) != 0) 476 goto out; 477 } 478 if (provider != NULL) { 479 if ((r = sshbuf_put_u8(m, 480 SSH_AGENT_CONSTRAIN_EXTENSION)) != 0 || 481 (r = sshbuf_put_cstring(m, 482 "sk-provider@openssh.com")) != 0 || 483 (r = sshbuf_put_cstring(m, provider)) != 0) 484 goto out; 485 } 486 r = 0; 487 out: 488 return r; 489 } 490 491 /* 492 * Adds an identity to the authentication server. 493 * This call is intended only for use by ssh-add(1) and like applications. 494 */ 495 int 496 ssh_add_identity_constrained(int sock, struct sshkey *key, 497 const char *comment, u_int life, u_int confirm, u_int maxsign, 498 const char *provider) 499 { 500 struct sshbuf *msg; 501 int r, constrained = (life || confirm || maxsign || provider); 502 u_char type; 503 504 if ((msg = sshbuf_new()) == NULL) 505 return SSH_ERR_ALLOC_FAIL; 506 507 switch (key->type) { 508 #ifdef WITH_OPENSSL 509 case KEY_RSA: 510 case KEY_RSA_CERT: 511 case KEY_DSA: 512 case KEY_DSA_CERT: 513 case KEY_ECDSA: 514 case KEY_ECDSA_CERT: 515 case KEY_ECDSA_SK: 516 case KEY_ECDSA_SK_CERT: 517 #endif 518 case KEY_ED25519: 519 case KEY_ED25519_CERT: 520 case KEY_ED25519_SK: 521 case KEY_ED25519_SK_CERT: 522 case KEY_XMSS: 523 case KEY_XMSS_CERT: 524 type = constrained ? 525 SSH2_AGENTC_ADD_ID_CONSTRAINED : 526 SSH2_AGENTC_ADD_IDENTITY; 527 if ((r = sshbuf_put_u8(msg, type)) != 0 || 528 (r = sshkey_private_serialize_maxsign(key, msg, maxsign, 529 0)) != 0 || 530 (r = sshbuf_put_cstring(msg, comment)) != 0) 531 goto out; 532 break; 533 default: 534 r = SSH_ERR_INVALID_ARGUMENT; 535 goto out; 536 } 537 if (constrained && 538 (r = encode_constraints(msg, life, confirm, maxsign, 539 provider)) != 0) 540 goto out; 541 if ((r = ssh_request_reply_decode(sock, msg)) != 0) 542 goto out; 543 /* success */ 544 r = 0; 545 out: 546 sshbuf_free(msg); 547 return r; 548 } 549 550 /* 551 * Removes an identity from the authentication server. 552 * This call is intended only for use by ssh-add(1) and like applications. 553 */ 554 int 555 ssh_remove_identity(int sock, const struct sshkey *key) 556 { 557 struct sshbuf *msg; 558 int r; 559 u_char *blob = NULL; 560 size_t blen; 561 562 if ((msg = sshbuf_new()) == NULL) 563 return SSH_ERR_ALLOC_FAIL; 564 565 if (key->type != KEY_UNSPEC) { 566 if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) 567 goto out; 568 if ((r = sshbuf_put_u8(msg, 569 SSH2_AGENTC_REMOVE_IDENTITY)) != 0 || 570 (r = sshbuf_put_string(msg, blob, blen)) != 0) 571 goto out; 572 } else { 573 r = SSH_ERR_INVALID_ARGUMENT; 574 goto out; 575 } 576 if ((r = ssh_request_reply_decode(sock, msg)) != 0) 577 goto out; 578 /* success */ 579 r = 0; 580 out: 581 if (blob != NULL) 582 freezero(blob, blen); 583 sshbuf_free(msg); 584 return r; 585 } 586 587 /* 588 * Add/remove an token-based identity from the authentication server. 589 * This call is intended only for use by ssh-add(1) and like applications. 590 */ 591 int 592 ssh_update_card(int sock, int add, const char *reader_id, const char *pin, 593 u_int life, u_int confirm) 594 { 595 struct sshbuf *msg; 596 int r, constrained = (life || confirm); 597 u_char type; 598 599 if (add) { 600 type = constrained ? 601 SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED : 602 SSH_AGENTC_ADD_SMARTCARD_KEY; 603 } else 604 type = SSH_AGENTC_REMOVE_SMARTCARD_KEY; 605 606 if ((msg = sshbuf_new()) == NULL) 607 return SSH_ERR_ALLOC_FAIL; 608 if ((r = sshbuf_put_u8(msg, type)) != 0 || 609 (r = sshbuf_put_cstring(msg, reader_id)) != 0 || 610 (r = sshbuf_put_cstring(msg, pin)) != 0) 611 goto out; 612 if (constrained && 613 (r = encode_constraints(msg, life, confirm, 0, NULL)) != 0) 614 goto out; 615 if ((r = ssh_request_reply_decode(sock, msg)) != 0) 616 goto out; 617 /* success */ 618 r = 0; 619 out: 620 sshbuf_free(msg); 621 return r; 622 } 623 624 /* 625 * Removes all identities from the agent. 626 * This call is intended only for use by ssh-add(1) and like applications. 627 * 628 * This supports the SSH protocol 1 message to because, when clearing all 629 * keys from an agent, we generally want to clear both protocol v1 and v2 630 * keys. 631 */ 632 int 633 ssh_remove_all_identities(int sock, int version) 634 { 635 struct sshbuf *msg; 636 u_char type = (version == 1) ? 637 SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES : 638 SSH2_AGENTC_REMOVE_ALL_IDENTITIES; 639 int r; 640 641 if ((msg = sshbuf_new()) == NULL) 642 return SSH_ERR_ALLOC_FAIL; 643 if ((r = sshbuf_put_u8(msg, type)) != 0) 644 goto out; 645 if ((r = ssh_request_reply_decode(sock, msg)) != 0) 646 goto out; 647 /* success */ 648 r = 0; 649 out: 650 sshbuf_free(msg); 651 return r; 652 } 653