1 /* $OpenBSD: authfd.c,v 1.118 2019/10/31 21:19:14 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 <unistd.h> 48 #include <errno.h> 49 50 #include "xmalloc.h" 51 #include "ssh.h" 52 #include "sshbuf.h" 53 #include "sshkey.h" 54 #include "authfd.h" 55 #include "cipher.h" 56 #include "compat.h" 57 #include "log.h" 58 #include "atomicio.h" 59 #include "misc.h" 60 #include "ssherr.h" 61 62 #define MAX_AGENT_IDENTITIES 2048 /* Max keys in agent reply */ 63 #define MAX_AGENT_REPLY_LEN (256 * 1024) /* Max bytes in agent reply */ 64 65 /* macro to check for "agent failure" message */ 66 #define agent_failed(x) \ 67 ((x == SSH_AGENT_FAILURE) || \ 68 (x == SSH_COM_AGENT2_FAILURE) || \ 69 (x == SSH2_AGENT_FAILURE)) 70 71 /* Convert success/failure response from agent to a err.h status */ 72 static int 73 decode_reply(u_char type) 74 { 75 if (agent_failed(type)) 76 return SSH_ERR_AGENT_FAILURE; 77 else if (type == SSH_AGENT_SUCCESS) 78 return 0; 79 else 80 return SSH_ERR_INVALID_FORMAT; 81 } 82 83 /* Returns the number of the authentication fd, or -1 if there is none. */ 84 int 85 ssh_get_authentication_socket(int *fdp) 86 { 87 const char *authsocket; 88 int sock, oerrno; 89 struct sockaddr_un sunaddr; 90 91 if (fdp != NULL) 92 *fdp = -1; 93 94 authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME); 95 if (authsocket == NULL || *authsocket == '\0') 96 return SSH_ERR_AGENT_NOT_PRESENT; 97 98 memset(&sunaddr, 0, sizeof(sunaddr)); 99 sunaddr.sun_family = AF_UNIX; 100 strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path)); 101 102 if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) 103 return SSH_ERR_SYSTEM_ERROR; 104 105 /* close on exec */ 106 if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 || 107 connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) == -1) { 108 oerrno = errno; 109 close(sock); 110 errno = oerrno; 111 return SSH_ERR_SYSTEM_ERROR; 112 } 113 if (fdp != NULL) 114 *fdp = sock; 115 else 116 close(sock); 117 return 0; 118 } 119 120 /* Communicate with agent: send request and read reply */ 121 static int 122 ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply) 123 { 124 int r; 125 size_t l, len; 126 char buf[1024]; 127 128 /* Get the length of the message, and format it in the buffer. */ 129 len = sshbuf_len(request); 130 POKE_U32(buf, len); 131 132 /* Send the length and then the packet to the agent. */ 133 if (atomicio(vwrite, sock, buf, 4) != 4 || 134 atomicio(vwrite, sock, sshbuf_mutable_ptr(request), 135 sshbuf_len(request)) != sshbuf_len(request)) 136 return SSH_ERR_AGENT_COMMUNICATION; 137 /* 138 * Wait for response from the agent. First read the length of the 139 * response packet. 140 */ 141 if (atomicio(read, sock, buf, 4) != 4) 142 return SSH_ERR_AGENT_COMMUNICATION; 143 144 /* Extract the length, and check it for sanity. */ 145 len = PEEK_U32(buf); 146 if (len > MAX_AGENT_REPLY_LEN) 147 return SSH_ERR_INVALID_FORMAT; 148 149 /* Read the rest of the response in to the buffer. */ 150 sshbuf_reset(reply); 151 while (len > 0) { 152 l = len; 153 if (l > sizeof(buf)) 154 l = sizeof(buf); 155 if (atomicio(read, sock, buf, l) != l) 156 return SSH_ERR_AGENT_COMMUNICATION; 157 if ((r = sshbuf_put(reply, buf, l)) != 0) 158 return r; 159 len -= l; 160 } 161 return 0; 162 } 163 164 /* 165 * Closes the agent socket if it should be closed (depends on how it was 166 * obtained). The argument must have been returned by 167 * ssh_get_authentication_socket(). 168 */ 169 void 170 ssh_close_authentication_socket(int sock) 171 { 172 if (getenv(SSH_AUTHSOCKET_ENV_NAME)) 173 close(sock); 174 } 175 176 /* Lock/unlock agent */ 177 int 178 ssh_lock_agent(int sock, int lock, const char *password) 179 { 180 int r; 181 u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK; 182 struct sshbuf *msg; 183 184 if ((msg = sshbuf_new()) == NULL) 185 return SSH_ERR_ALLOC_FAIL; 186 if ((r = sshbuf_put_u8(msg, type)) != 0 || 187 (r = sshbuf_put_cstring(msg, password)) != 0) 188 goto out; 189 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 190 goto out; 191 if ((r = sshbuf_get_u8(msg, &type)) != 0) 192 goto out; 193 r = decode_reply(type); 194 out: 195 sshbuf_free(msg); 196 return r; 197 } 198 199 200 static int 201 deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp) 202 { 203 int r; 204 char *comment = NULL; 205 const u_char *blob; 206 size_t blen; 207 208 if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 || 209 (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0) 210 goto out; 211 if ((r = sshkey_from_blob(blob, blen, keyp)) != 0) 212 goto out; 213 if (commentp != NULL) { 214 *commentp = comment; 215 comment = NULL; 216 } 217 r = 0; 218 out: 219 free(comment); 220 return r; 221 } 222 223 /* 224 * Fetch list of identities held by the agent. 225 */ 226 int 227 ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp) 228 { 229 u_char type; 230 u_int32_t num, i; 231 struct sshbuf *msg; 232 struct ssh_identitylist *idl = NULL; 233 int r; 234 235 /* 236 * Send a message to the agent requesting for a list of the 237 * identities it can represent. 238 */ 239 if ((msg = sshbuf_new()) == NULL) 240 return SSH_ERR_ALLOC_FAIL; 241 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0) 242 goto out; 243 244 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 245 goto out; 246 247 /* Get message type, and verify that we got a proper answer. */ 248 if ((r = sshbuf_get_u8(msg, &type)) != 0) 249 goto out; 250 if (agent_failed(type)) { 251 r = SSH_ERR_AGENT_FAILURE; 252 goto out; 253 } else if (type != SSH2_AGENT_IDENTITIES_ANSWER) { 254 r = SSH_ERR_INVALID_FORMAT; 255 goto out; 256 } 257 258 /* Get the number of entries in the response and check it for sanity. */ 259 if ((r = sshbuf_get_u32(msg, &num)) != 0) 260 goto out; 261 if (num > MAX_AGENT_IDENTITIES) { 262 r = SSH_ERR_INVALID_FORMAT; 263 goto out; 264 } 265 if (num == 0) { 266 r = SSH_ERR_AGENT_NO_IDENTITIES; 267 goto out; 268 } 269 270 /* Deserialise the response into a list of keys/comments */ 271 if ((idl = calloc(1, sizeof(*idl))) == NULL || 272 (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL || 273 (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) { 274 r = SSH_ERR_ALLOC_FAIL; 275 goto out; 276 } 277 for (i = 0; i < num;) { 278 if ((r = deserialise_identity2(msg, &(idl->keys[i]), 279 &(idl->comments[i]))) != 0) { 280 if (r == SSH_ERR_KEY_TYPE_UNKNOWN) { 281 /* Gracefully skip unknown key types */ 282 num--; 283 continue; 284 } else 285 goto out; 286 } 287 i++; 288 } 289 idl->nkeys = num; 290 *idlp = idl; 291 idl = NULL; 292 r = 0; 293 out: 294 sshbuf_free(msg); 295 if (idl != NULL) 296 ssh_free_identitylist(idl); 297 return r; 298 } 299 300 void 301 ssh_free_identitylist(struct ssh_identitylist *idl) 302 { 303 size_t i; 304 305 if (idl == NULL) 306 return; 307 for (i = 0; i < idl->nkeys; i++) { 308 if (idl->keys != NULL) 309 sshkey_free(idl->keys[i]); 310 if (idl->comments != NULL) 311 free(idl->comments[i]); 312 } 313 free(idl->keys); 314 free(idl->comments); 315 free(idl); 316 } 317 318 /* 319 * Check if the ssh agent has a given key. 320 * Returns 0 if found, or a negative SSH_ERR_* error code on failure. 321 */ 322 int 323 ssh_agent_has_key(int sock, struct sshkey *key) 324 { 325 int r, ret = SSH_ERR_KEY_NOT_FOUND; 326 size_t i; 327 struct ssh_identitylist *idlist = NULL; 328 329 if ((r = ssh_fetch_identitylist(sock, &idlist)) < 0) { 330 return r; 331 } 332 333 for (i = 0; i < idlist->nkeys; i++) { 334 if (sshkey_equal_public(idlist->keys[i], key)) { 335 ret = 0; 336 break; 337 } 338 } 339 340 ssh_free_identitylist(idlist); 341 return ret; 342 } 343 344 /* 345 * Sends a challenge (typically from a server via ssh(1)) to the agent, 346 * and waits for a response from the agent. 347 * Returns true (non-zero) if the agent gave the correct answer, zero 348 * otherwise. 349 */ 350 351 352 /* encode signature algorithm in flag bits, so we can keep the msg format */ 353 static u_int 354 agent_encode_alg(const struct sshkey *key, const char *alg) 355 { 356 if (alg != NULL && sshkey_type_plain(key->type) == KEY_RSA) { 357 if (strcmp(alg, "rsa-sha2-256") == 0 || 358 strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0) 359 return SSH_AGENT_RSA_SHA2_256; 360 if (strcmp(alg, "rsa-sha2-512") == 0 || 361 strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0) 362 return SSH_AGENT_RSA_SHA2_512; 363 } 364 return 0; 365 } 366 367 /* ask agent to sign data, returns err.h code on error, 0 on success */ 368 int 369 ssh_agent_sign(int sock, const struct sshkey *key, 370 u_char **sigp, size_t *lenp, 371 const u_char *data, size_t datalen, const char *alg, u_int compat) 372 { 373 struct sshbuf *msg; 374 u_char *sig = NULL, type = 0; 375 size_t len = 0; 376 u_int flags = 0; 377 int r = SSH_ERR_INTERNAL_ERROR; 378 379 *sigp = NULL; 380 *lenp = 0; 381 382 if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE) 383 return SSH_ERR_INVALID_ARGUMENT; 384 if ((msg = sshbuf_new()) == NULL) 385 return SSH_ERR_ALLOC_FAIL; 386 flags |= agent_encode_alg(key, alg); 387 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 || 388 (r = sshkey_puts(key, msg)) != 0 || 389 (r = sshbuf_put_string(msg, data, datalen)) != 0 || 390 (r = sshbuf_put_u32(msg, flags)) != 0) 391 goto out; 392 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 393 goto out; 394 if ((r = sshbuf_get_u8(msg, &type)) != 0) 395 goto out; 396 if (agent_failed(type)) { 397 r = SSH_ERR_AGENT_FAILURE; 398 goto out; 399 } else if (type != SSH2_AGENT_SIGN_RESPONSE) { 400 r = SSH_ERR_INVALID_FORMAT; 401 goto out; 402 } 403 if ((r = sshbuf_get_string(msg, &sig, &len)) != 0) 404 goto out; 405 /* Check what we actually got back from the agent. */ 406 if ((r = sshkey_check_sigtype(sig, len, alg)) != 0) 407 goto out; 408 /* success */ 409 *sigp = sig; 410 *lenp = len; 411 sig = NULL; 412 len = 0; 413 r = 0; 414 out: 415 freezero(sig, len); 416 sshbuf_free(msg); 417 return r; 418 } 419 420 /* Encode key for a message to the agent. */ 421 422 423 static int 424 encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign, 425 const char *provider) 426 { 427 int r; 428 429 if (life != 0) { 430 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 || 431 (r = sshbuf_put_u32(m, life)) != 0) 432 goto out; 433 } 434 if (confirm != 0) { 435 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0) 436 goto out; 437 } 438 if (maxsign != 0) { 439 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 || 440 (r = sshbuf_put_u32(m, maxsign)) != 0) 441 goto out; 442 } 443 if (provider != NULL) { 444 if ((r = sshbuf_put_u8(m, 445 SSH_AGENT_CONSTRAIN_EXTENSION)) != 0 || 446 (r = sshbuf_put_cstring(m, 447 "sk-provider@openssh.com")) != 0 || 448 (r = sshbuf_put_cstring(m, provider)) != 0) 449 goto out; 450 } 451 r = 0; 452 out: 453 return r; 454 } 455 456 /* 457 * Adds an identity to the authentication server. 458 * This call is intended only for use by ssh-add(1) and like applications. 459 */ 460 int 461 ssh_add_identity_constrained(int sock, struct sshkey *key, 462 const char *comment, u_int life, u_int confirm, u_int maxsign, 463 const char *provider) 464 { 465 struct sshbuf *msg; 466 int r, constrained = (life || confirm || maxsign || provider); 467 u_char type; 468 469 if ((msg = sshbuf_new()) == NULL) 470 return SSH_ERR_ALLOC_FAIL; 471 472 switch (key->type) { 473 #ifdef WITH_OPENSSL 474 case KEY_RSA: 475 case KEY_RSA_CERT: 476 case KEY_DSA: 477 case KEY_DSA_CERT: 478 case KEY_ECDSA: 479 case KEY_ECDSA_CERT: 480 case KEY_ECDSA_SK: 481 case KEY_ECDSA_SK_CERT: 482 #endif 483 case KEY_ED25519: 484 case KEY_ED25519_CERT: 485 case KEY_XMSS: 486 case KEY_XMSS_CERT: 487 type = constrained ? 488 SSH2_AGENTC_ADD_ID_CONSTRAINED : 489 SSH2_AGENTC_ADD_IDENTITY; 490 if ((r = sshbuf_put_u8(msg, type)) != 0 || 491 (r = sshkey_private_serialize_maxsign(key, msg, maxsign, 492 NULL)) != 0 || 493 (r = sshbuf_put_cstring(msg, comment)) != 0) 494 goto out; 495 break; 496 default: 497 r = SSH_ERR_INVALID_ARGUMENT; 498 goto out; 499 } 500 if (constrained && 501 (r = encode_constraints(msg, life, confirm, maxsign, 502 provider)) != 0) 503 goto out; 504 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 505 goto out; 506 if ((r = sshbuf_get_u8(msg, &type)) != 0) 507 goto out; 508 r = decode_reply(type); 509 out: 510 sshbuf_free(msg); 511 return r; 512 } 513 514 /* 515 * Removes an identity from the authentication server. 516 * This call is intended only for use by ssh-add(1) and like applications. 517 */ 518 int 519 ssh_remove_identity(int sock, struct sshkey *key) 520 { 521 struct sshbuf *msg; 522 int r; 523 u_char type, *blob = NULL; 524 size_t blen; 525 526 if ((msg = sshbuf_new()) == NULL) 527 return SSH_ERR_ALLOC_FAIL; 528 529 if (key->type != KEY_UNSPEC) { 530 if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) 531 goto out; 532 if ((r = sshbuf_put_u8(msg, 533 SSH2_AGENTC_REMOVE_IDENTITY)) != 0 || 534 (r = sshbuf_put_string(msg, blob, blen)) != 0) 535 goto out; 536 } else { 537 r = SSH_ERR_INVALID_ARGUMENT; 538 goto out; 539 } 540 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 541 goto out; 542 if ((r = sshbuf_get_u8(msg, &type)) != 0) 543 goto out; 544 r = decode_reply(type); 545 out: 546 if (blob != NULL) { 547 explicit_bzero(blob, blen); 548 free(blob); 549 } 550 sshbuf_free(msg); 551 return r; 552 } 553 554 /* 555 * Add/remove an token-based identity from the authentication server. 556 * This call is intended only for use by ssh-add(1) and like applications. 557 */ 558 int 559 ssh_update_card(int sock, int add, const char *reader_id, const char *pin, 560 u_int life, u_int confirm) 561 { 562 struct sshbuf *msg; 563 int r, constrained = (life || confirm); 564 u_char type; 565 566 if (add) { 567 type = constrained ? 568 SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED : 569 SSH_AGENTC_ADD_SMARTCARD_KEY; 570 } else 571 type = SSH_AGENTC_REMOVE_SMARTCARD_KEY; 572 573 if ((msg = sshbuf_new()) == NULL) 574 return SSH_ERR_ALLOC_FAIL; 575 if ((r = sshbuf_put_u8(msg, type)) != 0 || 576 (r = sshbuf_put_cstring(msg, reader_id)) != 0 || 577 (r = sshbuf_put_cstring(msg, pin)) != 0) 578 goto out; 579 if (constrained && 580 (r = encode_constraints(msg, life, confirm, 0, NULL)) != 0) 581 goto out; 582 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 583 goto out; 584 if ((r = sshbuf_get_u8(msg, &type)) != 0) 585 goto out; 586 r = decode_reply(type); 587 out: 588 sshbuf_free(msg); 589 return r; 590 } 591 592 /* 593 * Removes all identities from the agent. 594 * This call is intended only for use by ssh-add(1) and like applications. 595 * 596 * This supports the SSH protocol 1 message to because, when clearing all 597 * keys from an agent, we generally want to clear both protocol v1 and v2 598 * keys. 599 */ 600 int 601 ssh_remove_all_identities(int sock, int version) 602 { 603 struct sshbuf *msg; 604 u_char type = (version == 1) ? 605 SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES : 606 SSH2_AGENTC_REMOVE_ALL_IDENTITIES; 607 int r; 608 609 if ((msg = sshbuf_new()) == NULL) 610 return SSH_ERR_ALLOC_FAIL; 611 if ((r = sshbuf_put_u8(msg, type)) != 0) 612 goto out; 613 if ((r = ssh_request_reply(sock, msg, msg)) != 0) 614 goto out; 615 if ((r = sshbuf_get_u8(msg, &type)) != 0) 616 goto out; 617 r = decode_reply(type); 618 out: 619 sshbuf_free(msg); 620 return r; 621 } 622