1 /* $OpenBSD: authfd.c,v 1.120 2019/11/13 04:47:52 deraadt 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 39 #include <sys/types.h> 40 #include <sys/un.h> 41 #include <sys/socket.h> 42 43 #include <fcntl.h> 44 #include <stdlib.h> 45 #include <signal.h> 46 #include <string.h> 47 #include <stdarg.h> 48 #include <unistd.h> 49 #include <errno.h> 50 51 #include "xmalloc.h" 52 #include "ssh.h" 53 #include "sshbuf.h" 54 #include "sshkey.h" 55 #include "authfd.h" 56 #include "cipher.h" 57 #include "compat.h" 58 #include "log.h" 59 #include "atomicio.h" 60 #include "misc.h" 61 #include "ssherr.h" 62 63 #define MAX_AGENT_IDENTITIES 2048 /* Max keys in agent reply */ 64 #define MAX_AGENT_REPLY_LEN (256 * 1024) /* Max bytes in agent reply */ 65 66 /* macro to check for "agent failure" message */ 67 #define agent_failed(x) \ 68 ((x == SSH_AGENT_FAILURE) || \ 69 (x == SSH_COM_AGENT2_FAILURE) || \ 70 (x == SSH2_AGENT_FAILURE)) 71 72 /* Convert success/failure response from agent to a err.h status */ 73 static int 74 decode_reply(u_char type) 75 { 76 if (agent_failed(type)) 77 return SSH_ERR_AGENT_FAILURE; 78 else if (type == SSH_AGENT_SUCCESS) 79 return 0; 80 else 81 return SSH_ERR_INVALID_FORMAT; 82 } 83 84 /* Returns the number of the authentication fd, or -1 if there is none. */ 85 int 86 ssh_get_authentication_socket(int *fdp) 87 { 88 const char *authsocket; 89 int sock, oerrno; 90 struct sockaddr_un sunaddr; 91 92 if (fdp != NULL) 93 *fdp = -1; 94 95 authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME); 96 if (authsocket == NULL || *authsocket == '\0') 97 return SSH_ERR_AGENT_NOT_PRESENT; 98 99 memset(&sunaddr, 0, sizeof(sunaddr)); 100 sunaddr.sun_family = AF_UNIX; 101 strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path)); 102 103 if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) 104 return SSH_ERR_SYSTEM_ERROR; 105 106 /* close on exec */ 107 if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 || 108 connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) == -1) { 109 oerrno = errno; 110 close(sock); 111 errno = oerrno; 112 return SSH_ERR_SYSTEM_ERROR; 113 } 114 if (fdp != NULL) 115 *fdp = sock; 116 else 117 close(sock); 118 return 0; 119 } 120 121 /* Communicate with agent: send request and read reply */ 122 static int 123 ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply) 124 { 125 int r; 126 size_t l, len; 127 char buf[1024]; 128 129 /* Get the length of the message, and format it in the buffer. */ 130 len = sshbuf_len(request); 131 POKE_U32(buf, len); 132 133 /* Send the length and then the packet to the agent. */ 134 if (atomicio(vwrite, sock, buf, 4) != 4 || 135 atomicio(vwrite, sock, sshbuf_mutable_ptr(request), 136 sshbuf_len(request)) != sshbuf_len(request)) 137 return SSH_ERR_AGENT_COMMUNICATION; 138 /* 139 * Wait for response from the agent. First read the length of the 140 * response packet. 141 */ 142 if (atomicio(read, sock, buf, 4) != 4) 143 return SSH_ERR_AGENT_COMMUNICATION; 144 145 /* Extract the length, and check it for sanity. */ 146 len = PEEK_U32(buf); 147 if (len > MAX_AGENT_REPLY_LEN) 148 return SSH_ERR_INVALID_FORMAT; 149 150 /* Read the rest of the response in to the buffer. */ 151 sshbuf_reset(reply); 152 while (len > 0) { 153 l = len; 154 if (l > sizeof(buf)) 155 l = sizeof(buf); 156 if (atomicio(read, sock, buf, l) != l) 157 return SSH_ERR_AGENT_COMMUNICATION; 158 if ((r = sshbuf_put(reply, buf, l)) != 0) 159 return r; 160 len -= l; 161 } 162 return 0; 163 } 164 165 /* 166 * Closes the agent socket if it should be closed (depends on how it was 167 * obtained). The argument must have been returned by 168 * ssh_get_authentication_socket(). 169 */ 170 void 171 ssh_close_authentication_socket(int sock) 172 { 173 if (getenv(SSH_AUTHSOCKET_ENV_NAME)) 174 close(sock); 175 } 176 177 /* Lock/unlock agent */ 178 int 179 ssh_lock_agent(int sock, int lock, const char *password) 180 { 181 int r; 182 u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK; 183 struct sshbuf *msg; 184 185 if ((msg = sshbuf_new()) == NULL) 186 return SSH_ERR_ALLOC_FAIL; 187 if ((r = sshbuf_put_u8(msg, type)) != 0 || 188 (r = sshbuf_put_cstring(msg, password)) != 0) 189 goto out; 190 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 191 goto out; 192 if ((r = sshbuf_get_u8(msg, &type)) != 0) 193 goto out; 194 r = decode_reply(type); 195 out: 196 sshbuf_free(msg); 197 return r; 198 } 199 200 201 static int 202 deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp) 203 { 204 int r; 205 char *comment = NULL; 206 const u_char *blob; 207 size_t blen; 208 209 if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 || 210 (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0) 211 goto out; 212 if ((r = sshkey_from_blob(blob, blen, keyp)) != 0) 213 goto out; 214 if (commentp != NULL) { 215 *commentp = comment; 216 comment = NULL; 217 } 218 r = 0; 219 out: 220 free(comment); 221 return r; 222 } 223 224 /* 225 * Fetch list of identities held by the agent. 226 */ 227 int 228 ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp) 229 { 230 u_char type; 231 u_int32_t num, i; 232 struct sshbuf *msg; 233 struct ssh_identitylist *idl = NULL; 234 int r; 235 236 /* 237 * Send a message to the agent requesting for a list of the 238 * identities it can represent. 239 */ 240 if ((msg = sshbuf_new()) == NULL) 241 return SSH_ERR_ALLOC_FAIL; 242 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0) 243 goto out; 244 245 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 246 goto out; 247 248 /* Get message type, and verify that we got a proper answer. */ 249 if ((r = sshbuf_get_u8(msg, &type)) != 0) 250 goto out; 251 if (agent_failed(type)) { 252 r = SSH_ERR_AGENT_FAILURE; 253 goto out; 254 } else if (type != SSH2_AGENT_IDENTITIES_ANSWER) { 255 r = SSH_ERR_INVALID_FORMAT; 256 goto out; 257 } 258 259 /* Get the number of entries in the response and check it for sanity. */ 260 if ((r = sshbuf_get_u32(msg, &num)) != 0) 261 goto out; 262 if (num > MAX_AGENT_IDENTITIES) { 263 r = SSH_ERR_INVALID_FORMAT; 264 goto out; 265 } 266 if (num == 0) { 267 r = SSH_ERR_AGENT_NO_IDENTITIES; 268 goto out; 269 } 270 271 /* Deserialise the response into a list of keys/comments */ 272 if ((idl = calloc(1, sizeof(*idl))) == NULL || 273 (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL || 274 (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) { 275 r = SSH_ERR_ALLOC_FAIL; 276 goto out; 277 } 278 for (i = 0; i < num;) { 279 if ((r = deserialise_identity2(msg, &(idl->keys[i]), 280 &(idl->comments[i]))) != 0) { 281 if (r == SSH_ERR_KEY_TYPE_UNKNOWN) { 282 /* Gracefully skip unknown key types */ 283 num--; 284 continue; 285 } else 286 goto out; 287 } 288 i++; 289 } 290 idl->nkeys = num; 291 *idlp = idl; 292 idl = NULL; 293 r = 0; 294 out: 295 sshbuf_free(msg); 296 if (idl != NULL) 297 ssh_free_identitylist(idl); 298 return r; 299 } 300 301 void 302 ssh_free_identitylist(struct ssh_identitylist *idl) 303 { 304 size_t i; 305 306 if (idl == NULL) 307 return; 308 for (i = 0; i < idl->nkeys; i++) { 309 if (idl->keys != NULL) 310 sshkey_free(idl->keys[i]); 311 if (idl->comments != NULL) 312 free(idl->comments[i]); 313 } 314 free(idl->keys); 315 free(idl->comments); 316 free(idl); 317 } 318 319 /* 320 * Check if the ssh agent has a given key. 321 * Returns 0 if found, or a negative SSH_ERR_* error code on failure. 322 */ 323 int 324 ssh_agent_has_key(int sock, struct sshkey *key) 325 { 326 int r, ret = SSH_ERR_KEY_NOT_FOUND; 327 size_t i; 328 struct ssh_identitylist *idlist = NULL; 329 330 if ((r = ssh_fetch_identitylist(sock, &idlist)) < 0) { 331 return r; 332 } 333 334 for (i = 0; i < idlist->nkeys; i++) { 335 if (sshkey_equal_public(idlist->keys[i], key)) { 336 ret = 0; 337 break; 338 } 339 } 340 341 ssh_free_identitylist(idlist); 342 return ret; 343 } 344 345 /* 346 * Sends a challenge (typically from a server via ssh(1)) to the agent, 347 * and waits for a response from the agent. 348 * Returns true (non-zero) if the agent gave the correct answer, zero 349 * otherwise. 350 */ 351 352 353 /* encode signature algorithm in flag bits, so we can keep the msg format */ 354 static u_int 355 agent_encode_alg(const struct sshkey *key, const char *alg) 356 { 357 if (alg != NULL && sshkey_type_plain(key->type) == KEY_RSA) { 358 if (strcmp(alg, "rsa-sha2-256") == 0 || 359 strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0) 360 return SSH_AGENT_RSA_SHA2_256; 361 if (strcmp(alg, "rsa-sha2-512") == 0 || 362 strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0) 363 return SSH_AGENT_RSA_SHA2_512; 364 } 365 return 0; 366 } 367 368 /* ask agent to sign data, returns err.h code on error, 0 on success */ 369 int 370 ssh_agent_sign(int sock, const struct sshkey *key, 371 u_char **sigp, size_t *lenp, 372 const u_char *data, size_t datalen, const char *alg, u_int compat) 373 { 374 struct sshbuf *msg; 375 u_char *sig = NULL, type = 0; 376 size_t len = 0; 377 u_int flags = 0; 378 int r = SSH_ERR_INTERNAL_ERROR; 379 380 *sigp = NULL; 381 *lenp = 0; 382 383 if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE) 384 return SSH_ERR_INVALID_ARGUMENT; 385 if ((msg = sshbuf_new()) == NULL) 386 return SSH_ERR_ALLOC_FAIL; 387 flags |= agent_encode_alg(key, alg); 388 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 || 389 (r = sshkey_puts(key, msg)) != 0 || 390 (r = sshbuf_put_string(msg, data, datalen)) != 0 || 391 (r = sshbuf_put_u32(msg, flags)) != 0) 392 goto out; 393 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 394 goto out; 395 if ((r = sshbuf_get_u8(msg, &type)) != 0) 396 goto out; 397 if (agent_failed(type)) { 398 r = SSH_ERR_AGENT_FAILURE; 399 goto out; 400 } else if (type != SSH2_AGENT_SIGN_RESPONSE) { 401 r = SSH_ERR_INVALID_FORMAT; 402 goto out; 403 } 404 if ((r = sshbuf_get_string(msg, &sig, &len)) != 0) 405 goto out; 406 /* Check what we actually got back from the agent. */ 407 if ((r = sshkey_check_sigtype(sig, len, alg)) != 0) 408 goto out; 409 /* success */ 410 *sigp = sig; 411 *lenp = len; 412 sig = NULL; 413 len = 0; 414 r = 0; 415 out: 416 freezero(sig, len); 417 sshbuf_free(msg); 418 return r; 419 } 420 421 /* Encode key for a message to the agent. */ 422 423 424 static int 425 encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign, 426 const char *provider) 427 { 428 int r; 429 430 if (life != 0) { 431 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 || 432 (r = sshbuf_put_u32(m, life)) != 0) 433 goto out; 434 } 435 if (confirm != 0) { 436 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0) 437 goto out; 438 } 439 if (maxsign != 0) { 440 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 || 441 (r = sshbuf_put_u32(m, maxsign)) != 0) 442 goto out; 443 } 444 if (provider != NULL) { 445 if ((r = sshbuf_put_u8(m, 446 SSH_AGENT_CONSTRAIN_EXTENSION)) != 0 || 447 (r = sshbuf_put_cstring(m, 448 "sk-provider@openssh.com")) != 0 || 449 (r = sshbuf_put_cstring(m, provider)) != 0) 450 goto out; 451 } 452 r = 0; 453 out: 454 return r; 455 } 456 457 /* 458 * Adds an identity to the authentication server. 459 * This call is intended only for use by ssh-add(1) and like applications. 460 */ 461 int 462 ssh_add_identity_constrained(int sock, struct sshkey *key, 463 const char *comment, u_int life, u_int confirm, u_int maxsign, 464 const char *provider) 465 { 466 struct sshbuf *msg; 467 int r, constrained = (life || confirm || maxsign || provider); 468 u_char type; 469 470 if ((msg = sshbuf_new()) == NULL) 471 return SSH_ERR_ALLOC_FAIL; 472 473 switch (key->type) { 474 #ifdef WITH_OPENSSL 475 case KEY_RSA: 476 case KEY_RSA_CERT: 477 case KEY_DSA: 478 case KEY_DSA_CERT: 479 case KEY_ECDSA: 480 case KEY_ECDSA_CERT: 481 case KEY_ECDSA_SK: 482 case KEY_ECDSA_SK_CERT: 483 #endif 484 case KEY_ED25519: 485 case KEY_ED25519_CERT: 486 case KEY_ED25519_SK: 487 case KEY_ED25519_SK_CERT: 488 case KEY_XMSS: 489 case KEY_XMSS_CERT: 490 type = constrained ? 491 SSH2_AGENTC_ADD_ID_CONSTRAINED : 492 SSH2_AGENTC_ADD_IDENTITY; 493 if ((r = sshbuf_put_u8(msg, type)) != 0 || 494 (r = sshkey_private_serialize_maxsign(key, msg, maxsign, 495 NULL)) != 0 || 496 (r = sshbuf_put_cstring(msg, comment)) != 0) 497 goto out; 498 break; 499 default: 500 r = SSH_ERR_INVALID_ARGUMENT; 501 goto out; 502 } 503 if (constrained && 504 (r = encode_constraints(msg, life, confirm, maxsign, 505 provider)) != 0) 506 goto out; 507 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 508 goto out; 509 if ((r = sshbuf_get_u8(msg, &type)) != 0) 510 goto out; 511 r = decode_reply(type); 512 out: 513 sshbuf_free(msg); 514 return r; 515 } 516 517 /* 518 * Removes an identity from the authentication server. 519 * This call is intended only for use by ssh-add(1) and like applications. 520 */ 521 int 522 ssh_remove_identity(int sock, struct sshkey *key) 523 { 524 struct sshbuf *msg; 525 int r; 526 u_char type, *blob = NULL; 527 size_t blen; 528 529 if ((msg = sshbuf_new()) == NULL) 530 return SSH_ERR_ALLOC_FAIL; 531 532 if (key->type != KEY_UNSPEC) { 533 if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) 534 goto out; 535 if ((r = sshbuf_put_u8(msg, 536 SSH2_AGENTC_REMOVE_IDENTITY)) != 0 || 537 (r = sshbuf_put_string(msg, blob, blen)) != 0) 538 goto out; 539 } else { 540 r = SSH_ERR_INVALID_ARGUMENT; 541 goto out; 542 } 543 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 544 goto out; 545 if ((r = sshbuf_get_u8(msg, &type)) != 0) 546 goto out; 547 r = decode_reply(type); 548 out: 549 if (blob != NULL) { 550 explicit_bzero(blob, blen); 551 free(blob); 552 } 553 sshbuf_free(msg); 554 return r; 555 } 556 557 /* 558 * Add/remove an token-based identity from the authentication server. 559 * This call is intended only for use by ssh-add(1) and like applications. 560 */ 561 int 562 ssh_update_card(int sock, int add, const char *reader_id, const char *pin, 563 u_int life, u_int confirm) 564 { 565 struct sshbuf *msg; 566 int r, constrained = (life || confirm); 567 u_char type; 568 569 if (add) { 570 type = constrained ? 571 SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED : 572 SSH_AGENTC_ADD_SMARTCARD_KEY; 573 } else 574 type = SSH_AGENTC_REMOVE_SMARTCARD_KEY; 575 576 if ((msg = sshbuf_new()) == NULL) 577 return SSH_ERR_ALLOC_FAIL; 578 if ((r = sshbuf_put_u8(msg, type)) != 0 || 579 (r = sshbuf_put_cstring(msg, reader_id)) != 0 || 580 (r = sshbuf_put_cstring(msg, pin)) != 0) 581 goto out; 582 if (constrained && 583 (r = encode_constraints(msg, life, confirm, 0, NULL)) != 0) 584 goto out; 585 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 586 goto out; 587 if ((r = sshbuf_get_u8(msg, &type)) != 0) 588 goto out; 589 r = decode_reply(type); 590 out: 591 sshbuf_free(msg); 592 return r; 593 } 594 595 /* 596 * Removes all identities from the agent. 597 * This call is intended only for use by ssh-add(1) and like applications. 598 * 599 * This supports the SSH protocol 1 message to because, when clearing all 600 * keys from an agent, we generally want to clear both protocol v1 and v2 601 * keys. 602 */ 603 int 604 ssh_remove_all_identities(int sock, int version) 605 { 606 struct sshbuf *msg; 607 u_char type = (version == 1) ? 608 SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES : 609 SSH2_AGENTC_REMOVE_ALL_IDENTITIES; 610 int r; 611 612 if ((msg = sshbuf_new()) == NULL) 613 return SSH_ERR_ALLOC_FAIL; 614 if ((r = sshbuf_put_u8(msg, type)) != 0) 615 goto out; 616 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 617 goto out; 618 if ((r = sshbuf_get_u8(msg, &type)) != 0) 619 goto out; 620 r = decode_reply(type); 621 out: 622 sshbuf_free(msg); 623 return r; 624 } 625