1 /* $OpenBSD: authfd.c,v 1.124 2020/06/26 05:03:36 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 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 /* 85 * Opens an authentication socket at the provided path and stores the file 86 * descriptor in fdp. Returns 0 on success and an error on failure. 87 */ 88 int 89 ssh_get_authentication_socket_path(const char *authsocket, int *fdp) 90 { 91 int sock, oerrno; 92 struct sockaddr_un sunaddr; 93 94 memset(&sunaddr, 0, sizeof(sunaddr)); 95 sunaddr.sun_family = AF_UNIX; 96 strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path)); 97 98 if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) 99 return SSH_ERR_SYSTEM_ERROR; 100 101 /* close on exec */ 102 if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 || 103 connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) == -1) { 104 oerrno = errno; 105 close(sock); 106 errno = oerrno; 107 return SSH_ERR_SYSTEM_ERROR; 108 } 109 if (fdp != NULL) 110 *fdp = sock; 111 else 112 close(sock); 113 return 0; 114 } 115 116 /* 117 * Opens the default authentication socket and stores the file descriptor in 118 * fdp. Returns 0 on success and an error on failure. 119 */ 120 int 121 ssh_get_authentication_socket(int *fdp) 122 { 123 const char *authsocket; 124 125 if (fdp != NULL) 126 *fdp = -1; 127 128 authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME); 129 if (authsocket == NULL || *authsocket == '\0') 130 return SSH_ERR_AGENT_NOT_PRESENT; 131 132 return ssh_get_authentication_socket_path(authsocket, fdp); 133 } 134 135 /* Communicate with agent: send request and read reply */ 136 static int 137 ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply) 138 { 139 int r; 140 size_t l, len; 141 char buf[1024]; 142 143 /* Get the length of the message, and format it in the buffer. */ 144 len = sshbuf_len(request); 145 POKE_U32(buf, len); 146 147 /* Send the length and then the packet to the agent. */ 148 if (atomicio(vwrite, sock, buf, 4) != 4 || 149 atomicio(vwrite, sock, sshbuf_mutable_ptr(request), 150 sshbuf_len(request)) != sshbuf_len(request)) 151 return SSH_ERR_AGENT_COMMUNICATION; 152 /* 153 * Wait for response from the agent. First read the length of the 154 * response packet. 155 */ 156 if (atomicio(read, sock, buf, 4) != 4) 157 return SSH_ERR_AGENT_COMMUNICATION; 158 159 /* Extract the length, and check it for sanity. */ 160 len = PEEK_U32(buf); 161 if (len > MAX_AGENT_REPLY_LEN) 162 return SSH_ERR_INVALID_FORMAT; 163 164 /* Read the rest of the response in to the buffer. */ 165 sshbuf_reset(reply); 166 while (len > 0) { 167 l = len; 168 if (l > sizeof(buf)) 169 l = sizeof(buf); 170 if (atomicio(read, sock, buf, l) != l) 171 return SSH_ERR_AGENT_COMMUNICATION; 172 if ((r = sshbuf_put(reply, buf, l)) != 0) 173 return r; 174 len -= l; 175 } 176 return 0; 177 } 178 179 /* 180 * Closes the agent socket if it should be closed (depends on how it was 181 * obtained). The argument must have been returned by 182 * ssh_get_authentication_socket(). 183 */ 184 void 185 ssh_close_authentication_socket(int sock) 186 { 187 if (getenv(SSH_AUTHSOCKET_ENV_NAME)) 188 close(sock); 189 } 190 191 /* Lock/unlock agent */ 192 int 193 ssh_lock_agent(int sock, int lock, const char *password) 194 { 195 int r; 196 u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK; 197 struct sshbuf *msg; 198 199 if ((msg = sshbuf_new()) == NULL) 200 return SSH_ERR_ALLOC_FAIL; 201 if ((r = sshbuf_put_u8(msg, type)) != 0 || 202 (r = sshbuf_put_cstring(msg, password)) != 0) 203 goto out; 204 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 205 goto out; 206 if ((r = sshbuf_get_u8(msg, &type)) != 0) 207 goto out; 208 r = decode_reply(type); 209 out: 210 sshbuf_free(msg); 211 return r; 212 } 213 214 215 static int 216 deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp) 217 { 218 int r; 219 char *comment = NULL; 220 const u_char *blob; 221 size_t blen; 222 223 if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 || 224 (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0) 225 goto out; 226 if ((r = sshkey_from_blob(blob, blen, keyp)) != 0) 227 goto out; 228 if (commentp != NULL) { 229 *commentp = comment; 230 comment = NULL; 231 } 232 r = 0; 233 out: 234 free(comment); 235 return r; 236 } 237 238 /* 239 * Fetch list of identities held by the agent. 240 */ 241 int 242 ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp) 243 { 244 u_char type; 245 u_int32_t num, i; 246 struct sshbuf *msg; 247 struct ssh_identitylist *idl = NULL; 248 int r; 249 250 /* 251 * Send a message to the agent requesting for a list of the 252 * identities it can represent. 253 */ 254 if ((msg = sshbuf_new()) == NULL) 255 return SSH_ERR_ALLOC_FAIL; 256 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0) 257 goto out; 258 259 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 260 goto out; 261 262 /* Get message type, and verify that we got a proper answer. */ 263 if ((r = sshbuf_get_u8(msg, &type)) != 0) 264 goto out; 265 if (agent_failed(type)) { 266 r = SSH_ERR_AGENT_FAILURE; 267 goto out; 268 } else if (type != SSH2_AGENT_IDENTITIES_ANSWER) { 269 r = SSH_ERR_INVALID_FORMAT; 270 goto out; 271 } 272 273 /* Get the number of entries in the response and check it for sanity. */ 274 if ((r = sshbuf_get_u32(msg, &num)) != 0) 275 goto out; 276 if (num > MAX_AGENT_IDENTITIES) { 277 r = SSH_ERR_INVALID_FORMAT; 278 goto out; 279 } 280 if (num == 0) { 281 r = SSH_ERR_AGENT_NO_IDENTITIES; 282 goto out; 283 } 284 285 /* Deserialise the response into a list of keys/comments */ 286 if ((idl = calloc(1, sizeof(*idl))) == NULL || 287 (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL || 288 (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) { 289 r = SSH_ERR_ALLOC_FAIL; 290 goto out; 291 } 292 for (i = 0; i < num;) { 293 if ((r = deserialise_identity2(msg, &(idl->keys[i]), 294 &(idl->comments[i]))) != 0) { 295 if (r == SSH_ERR_KEY_TYPE_UNKNOWN) { 296 /* Gracefully skip unknown key types */ 297 num--; 298 continue; 299 } else 300 goto out; 301 } 302 i++; 303 } 304 idl->nkeys = num; 305 *idlp = idl; 306 idl = NULL; 307 r = 0; 308 out: 309 sshbuf_free(msg); 310 if (idl != NULL) 311 ssh_free_identitylist(idl); 312 return r; 313 } 314 315 void 316 ssh_free_identitylist(struct ssh_identitylist *idl) 317 { 318 size_t i; 319 320 if (idl == NULL) 321 return; 322 for (i = 0; i < idl->nkeys; i++) { 323 if (idl->keys != NULL) 324 sshkey_free(idl->keys[i]); 325 if (idl->comments != NULL) 326 free(idl->comments[i]); 327 } 328 free(idl->keys); 329 free(idl->comments); 330 free(idl); 331 } 332 333 /* 334 * Check if the ssh agent has a given key. 335 * Returns 0 if found, or a negative SSH_ERR_* error code on failure. 336 */ 337 int 338 ssh_agent_has_key(int sock, const struct sshkey *key) 339 { 340 int r, ret = SSH_ERR_KEY_NOT_FOUND; 341 size_t i; 342 struct ssh_identitylist *idlist = NULL; 343 344 if ((r = ssh_fetch_identitylist(sock, &idlist)) != 0) { 345 return r; 346 } 347 348 for (i = 0; i < idlist->nkeys; i++) { 349 if (sshkey_equal_public(idlist->keys[i], key)) { 350 ret = 0; 351 break; 352 } 353 } 354 355 ssh_free_identitylist(idlist); 356 return ret; 357 } 358 359 /* 360 * Sends a challenge (typically from a server via ssh(1)) to the agent, 361 * and waits for a response from the agent. 362 * Returns true (non-zero) if the agent gave the correct answer, zero 363 * otherwise. 364 */ 365 366 367 /* encode signature algorithm in flag bits, so we can keep the msg format */ 368 static u_int 369 agent_encode_alg(const struct sshkey *key, const char *alg) 370 { 371 if (alg != NULL && sshkey_type_plain(key->type) == KEY_RSA) { 372 if (strcmp(alg, "rsa-sha2-256") == 0 || 373 strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0) 374 return SSH_AGENT_RSA_SHA2_256; 375 if (strcmp(alg, "rsa-sha2-512") == 0 || 376 strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0) 377 return SSH_AGENT_RSA_SHA2_512; 378 } 379 return 0; 380 } 381 382 /* ask agent to sign data, returns err.h code on error, 0 on success */ 383 int 384 ssh_agent_sign(int sock, const struct sshkey *key, 385 u_char **sigp, size_t *lenp, 386 const u_char *data, size_t datalen, const char *alg, u_int compat) 387 { 388 struct sshbuf *msg; 389 u_char *sig = NULL, type = 0; 390 size_t len = 0; 391 u_int flags = 0; 392 int r = SSH_ERR_INTERNAL_ERROR; 393 394 *sigp = NULL; 395 *lenp = 0; 396 397 if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE) 398 return SSH_ERR_INVALID_ARGUMENT; 399 if ((msg = sshbuf_new()) == NULL) 400 return SSH_ERR_ALLOC_FAIL; 401 flags |= agent_encode_alg(key, alg); 402 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 || 403 (r = sshkey_puts(key, msg)) != 0 || 404 (r = sshbuf_put_string(msg, data, datalen)) != 0 || 405 (r = sshbuf_put_u32(msg, flags)) != 0) 406 goto out; 407 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 408 goto out; 409 if ((r = sshbuf_get_u8(msg, &type)) != 0) 410 goto out; 411 if (agent_failed(type)) { 412 r = SSH_ERR_AGENT_FAILURE; 413 goto out; 414 } else if (type != SSH2_AGENT_SIGN_RESPONSE) { 415 r = SSH_ERR_INVALID_FORMAT; 416 goto out; 417 } 418 if ((r = sshbuf_get_string(msg, &sig, &len)) != 0) 419 goto out; 420 /* Check what we actually got back from the agent. */ 421 if ((r = sshkey_check_sigtype(sig, len, alg)) != 0) 422 goto out; 423 /* success */ 424 *sigp = sig; 425 *lenp = len; 426 sig = NULL; 427 len = 0; 428 r = 0; 429 out: 430 freezero(sig, len); 431 sshbuf_free(msg); 432 return r; 433 } 434 435 /* Encode key for a message to the agent. */ 436 437 438 static int 439 encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign, 440 const char *provider) 441 { 442 int r; 443 444 if (life != 0) { 445 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 || 446 (r = sshbuf_put_u32(m, life)) != 0) 447 goto out; 448 } 449 if (confirm != 0) { 450 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0) 451 goto out; 452 } 453 if (maxsign != 0) { 454 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 || 455 (r = sshbuf_put_u32(m, maxsign)) != 0) 456 goto out; 457 } 458 if (provider != NULL) { 459 if ((r = sshbuf_put_u8(m, 460 SSH_AGENT_CONSTRAIN_EXTENSION)) != 0 || 461 (r = sshbuf_put_cstring(m, 462 "sk-provider@openssh.com")) != 0 || 463 (r = sshbuf_put_cstring(m, provider)) != 0) 464 goto out; 465 } 466 r = 0; 467 out: 468 return r; 469 } 470 471 /* 472 * Adds an identity to the authentication server. 473 * This call is intended only for use by ssh-add(1) and like applications. 474 */ 475 int 476 ssh_add_identity_constrained(int sock, struct sshkey *key, 477 const char *comment, u_int life, u_int confirm, u_int maxsign, 478 const char *provider) 479 { 480 struct sshbuf *msg; 481 int r, constrained = (life || confirm || maxsign || provider); 482 u_char type; 483 484 if ((msg = sshbuf_new()) == NULL) 485 return SSH_ERR_ALLOC_FAIL; 486 487 switch (key->type) { 488 #ifdef WITH_OPENSSL 489 case KEY_RSA: 490 case KEY_RSA_CERT: 491 case KEY_DSA: 492 case KEY_DSA_CERT: 493 case KEY_ECDSA: 494 case KEY_ECDSA_CERT: 495 case KEY_ECDSA_SK: 496 case KEY_ECDSA_SK_CERT: 497 #endif 498 case KEY_ED25519: 499 case KEY_ED25519_CERT: 500 case KEY_ED25519_SK: 501 case KEY_ED25519_SK_CERT: 502 case KEY_XMSS: 503 case KEY_XMSS_CERT: 504 type = constrained ? 505 SSH2_AGENTC_ADD_ID_CONSTRAINED : 506 SSH2_AGENTC_ADD_IDENTITY; 507 if ((r = sshbuf_put_u8(msg, type)) != 0 || 508 (r = sshkey_private_serialize_maxsign(key, msg, maxsign, 509 NULL)) != 0 || 510 (r = sshbuf_put_cstring(msg, comment)) != 0) 511 goto out; 512 break; 513 default: 514 r = SSH_ERR_INVALID_ARGUMENT; 515 goto out; 516 } 517 if (constrained && 518 (r = encode_constraints(msg, life, confirm, maxsign, 519 provider)) != 0) 520 goto out; 521 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 522 goto out; 523 if ((r = sshbuf_get_u8(msg, &type)) != 0) 524 goto out; 525 r = decode_reply(type); 526 out: 527 sshbuf_free(msg); 528 return r; 529 } 530 531 /* 532 * Removes an identity from the authentication server. 533 * This call is intended only for use by ssh-add(1) and like applications. 534 */ 535 int 536 ssh_remove_identity(int sock, const struct sshkey *key) 537 { 538 struct sshbuf *msg; 539 int r; 540 u_char type, *blob = NULL; 541 size_t blen; 542 543 if ((msg = sshbuf_new()) == NULL) 544 return SSH_ERR_ALLOC_FAIL; 545 546 if (key->type != KEY_UNSPEC) { 547 if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) 548 goto out; 549 if ((r = sshbuf_put_u8(msg, 550 SSH2_AGENTC_REMOVE_IDENTITY)) != 0 || 551 (r = sshbuf_put_string(msg, blob, blen)) != 0) 552 goto out; 553 } else { 554 r = SSH_ERR_INVALID_ARGUMENT; 555 goto out; 556 } 557 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 558 goto out; 559 if ((r = sshbuf_get_u8(msg, &type)) != 0) 560 goto out; 561 r = decode_reply(type); 562 out: 563 if (blob != NULL) 564 freezero(blob, blen); 565 sshbuf_free(msg); 566 return r; 567 } 568 569 /* 570 * Add/remove an token-based identity from the authentication server. 571 * This call is intended only for use by ssh-add(1) and like applications. 572 */ 573 int 574 ssh_update_card(int sock, int add, const char *reader_id, const char *pin, 575 u_int life, u_int confirm) 576 { 577 struct sshbuf *msg; 578 int r, constrained = (life || confirm); 579 u_char type; 580 581 if (add) { 582 type = constrained ? 583 SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED : 584 SSH_AGENTC_ADD_SMARTCARD_KEY; 585 } else 586 type = SSH_AGENTC_REMOVE_SMARTCARD_KEY; 587 588 if ((msg = sshbuf_new()) == NULL) 589 return SSH_ERR_ALLOC_FAIL; 590 if ((r = sshbuf_put_u8(msg, type)) != 0 || 591 (r = sshbuf_put_cstring(msg, reader_id)) != 0 || 592 (r = sshbuf_put_cstring(msg, pin)) != 0) 593 goto out; 594 if (constrained && 595 (r = encode_constraints(msg, life, confirm, 0, NULL)) != 0) 596 goto out; 597 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 598 goto out; 599 if ((r = sshbuf_get_u8(msg, &type)) != 0) 600 goto out; 601 r = decode_reply(type); 602 out: 603 sshbuf_free(msg); 604 return r; 605 } 606 607 /* 608 * Removes all identities from the agent. 609 * This call is intended only for use by ssh-add(1) and like applications. 610 * 611 * This supports the SSH protocol 1 message to because, when clearing all 612 * keys from an agent, we generally want to clear both protocol v1 and v2 613 * keys. 614 */ 615 int 616 ssh_remove_all_identities(int sock, int version) 617 { 618 struct sshbuf *msg; 619 u_char type = (version == 1) ? 620 SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES : 621 SSH2_AGENTC_REMOVE_ALL_IDENTITIES; 622 int r; 623 624 if ((msg = sshbuf_new()) == NULL) 625 return SSH_ERR_ALLOC_FAIL; 626 if ((r = sshbuf_put_u8(msg, type)) != 0) 627 goto out; 628 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 629 goto out; 630 if ((r = sshbuf_get_u8(msg, &type)) != 0) 631 goto out; 632 r = decode_reply(type); 633 out: 634 sshbuf_free(msg); 635 return r; 636 } 637