1/* $NetBSD: ssh-sk-client.c,v 1.6 2022/02/23 19:07:20 christos Exp $ */ 2/* $OpenBSD: ssh-sk-client.c,v 1.12 2022/01/14 03:34:00 djm Exp $ */ 3/* 4 * Copyright (c) 2019 Google LLC 5 * 6 * Permission to use, copy, modify, and distribute this software for any 7 * purpose with or without fee is hereby granted, provided that the above 8 * copyright notice and this permission notice appear in all copies. 9 * 10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 17 */ 18#include "includes.h" 19__RCSID("$NetBSD: ssh-sk-client.c,v 1.6 2022/02/23 19:07:20 christos Exp $"); 20 21#include <sys/types.h> 22#include <sys/socket.h> 23#include <sys/wait.h> 24 25#include <fcntl.h> 26#include <limits.h> 27#include <errno.h> 28#include <signal.h> 29#include <stdarg.h> 30#include <stdio.h> 31#include <stdlib.h> 32#include <string.h> 33#include <unistd.h> 34 35#include "log.h" 36#include "ssherr.h" 37#include "sshbuf.h" 38#include "sshkey.h" 39#include "msg.h" 40#include "digest.h" 41#include "pathnames.h" 42#include "ssh-sk.h" 43#include "misc.h" 44 45/* #define DEBUG_SK 1 */ 46 47static int 48start_helper(int *fdp, pid_t *pidp, void (**osigchldp)(int)) 49{ 50 void (*osigchld)(int); 51 int oerrno, pair[2]; 52 pid_t pid; 53 const char *helper, *verbosity = NULL; 54 55 *fdp = -1; 56 *pidp = 0; 57 *osigchldp = SIG_DFL; 58 59 helper = getenv("SSH_SK_HELPER"); 60 if (helper == NULL || strlen(helper) == 0) 61 helper = _PATH_SSH_SK_HELPER; 62 if (access(helper, X_OK) != 0) { 63 oerrno = errno; 64 error_f("helper \"%s\" unusable: %s", helper, strerror(errno)); 65 errno = oerrno; 66 return SSH_ERR_SYSTEM_ERROR; 67 } 68#ifdef DEBUG_SK 69 verbosity = "-vvv"; 70#endif 71 72 /* Start helper */ 73 if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) { 74 error("socketpair: %s", strerror(errno)); 75 return SSH_ERR_SYSTEM_ERROR; 76 } 77 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 78 if ((pid = fork()) == -1) { 79 oerrno = errno; 80 error("fork: %s", strerror(errno)); 81 close(pair[0]); 82 close(pair[1]); 83 ssh_signal(SIGCHLD, osigchld); 84 errno = oerrno; 85 return SSH_ERR_SYSTEM_ERROR; 86 } 87 if (pid == 0) { 88 if ((dup2(pair[1], STDIN_FILENO) == -1) || 89 (dup2(pair[1], STDOUT_FILENO) == -1)) { 90 error_f("dup2: %s", strerror(errno)); 91 _exit(1); 92 } 93 close(pair[0]); 94 close(pair[1]); 95 closefrom(STDERR_FILENO + 1); 96 debug_f("starting %s %s", helper, 97 verbosity == NULL ? "" : verbosity); 98 execlp(helper, helper, verbosity, (char *)NULL); 99 error_f("execlp: %s", strerror(errno)); 100 _exit(1); 101 } 102 close(pair[1]); 103 104 /* success */ 105 debug3_f("started pid=%ld", (long)pid); 106 *fdp = pair[0]; 107 *pidp = pid; 108 *osigchldp = osigchld; 109 return 0; 110} 111 112static int 113reap_helper(pid_t pid) 114{ 115 int status, oerrno; 116 117 debug3_f("pid=%ld", (long)pid); 118 119 errno = 0; 120 while (waitpid(pid, &status, 0) == -1) { 121 if (errno == EINTR) { 122 errno = 0; 123 continue; 124 } 125 oerrno = errno; 126 error_f("waitpid: %s", strerror(errno)); 127 errno = oerrno; 128 return SSH_ERR_SYSTEM_ERROR; 129 } 130 if (!WIFEXITED(status)) { 131 error_f("helper exited abnormally"); 132 return SSH_ERR_AGENT_FAILURE; 133 } else if (WEXITSTATUS(status) != 0) { 134 error_f("helper exited with non-zero exit status"); 135 return SSH_ERR_AGENT_FAILURE; 136 } 137 return 0; 138} 139 140static int 141client_converse(struct sshbuf *msg, struct sshbuf **respp, u_int type) 142{ 143 int oerrno, fd, r2, ll, r = SSH_ERR_INTERNAL_ERROR; 144 u_int rtype, rerr; 145 pid_t pid; 146 u_char version; 147 void (*osigchld)(int); 148 struct sshbuf *req = NULL, *resp = NULL; 149 *respp = NULL; 150 151 if ((r = start_helper(&fd, &pid, &osigchld)) != 0) 152 return r; 153 154 if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL) { 155 r = SSH_ERR_ALLOC_FAIL; 156 goto out; 157 } 158 /* Request preamble: type, log_on_stderr, log_level */ 159 ll = log_level_get(); 160 if ((r = sshbuf_put_u32(req, type)) != 0 || 161 (r = sshbuf_put_u8(req, log_is_on_stderr() != 0)) != 0 || 162 (r = sshbuf_put_u32(req, (uint32_t)(ll < 0 ? 0 : ll))) != 0 || 163 (r = sshbuf_putb(req, msg)) != 0) { 164 error_fr(r, "compose"); 165 goto out; 166 } 167 if ((r = ssh_msg_send(fd, SSH_SK_HELPER_VERSION, req)) != 0) { 168 error_fr(r, "send"); 169 goto out; 170 } 171 if ((r = ssh_msg_recv(fd, resp)) != 0) { 172 error_fr(r, "receive"); 173 goto out; 174 } 175 if ((r = sshbuf_get_u8(resp, &version)) != 0) { 176 error_fr(r, "parse version"); 177 goto out; 178 } 179 if (version != SSH_SK_HELPER_VERSION) { 180 error_f("unsupported version: got %u, expected %u", 181 version, SSH_SK_HELPER_VERSION); 182 r = SSH_ERR_INVALID_FORMAT; 183 goto out; 184 } 185 if ((r = sshbuf_get_u32(resp, &rtype)) != 0) { 186 error_fr(r, "parse message type"); 187 goto out; 188 } 189 if (rtype == SSH_SK_HELPER_ERROR) { 190 if ((r = sshbuf_get_u32(resp, &rerr)) != 0) { 191 error_fr(r, "parse"); 192 goto out; 193 } 194 debug_f("helper returned error -%u", rerr); 195 /* OpenSSH error values are negative; encoded as -err on wire */ 196 if (rerr == 0 || rerr >= INT_MAX) 197 r = SSH_ERR_INTERNAL_ERROR; 198 else 199 r = -(int)rerr; 200 goto out; 201 } else if (rtype != type) { 202 error_f("helper returned incorrect message type %u, " 203 "expecting %u", rtype, type); 204 r = SSH_ERR_INTERNAL_ERROR; 205 goto out; 206 } 207 /* success */ 208 r = 0; 209 out: 210 oerrno = errno; 211 close(fd); 212 if ((r2 = reap_helper(pid)) != 0) { 213 if (r == 0) { 214 r = r2; 215 oerrno = errno; 216 } 217 } 218 if (r == 0) { 219 *respp = resp; 220 resp = NULL; 221 } 222 sshbuf_free(req); 223 sshbuf_free(resp); 224 ssh_signal(SIGCHLD, osigchld); 225 errno = oerrno; 226 return r; 227 228} 229 230int 231sshsk_sign(const char *provider, struct sshkey *key, 232 u_char **sigp, size_t *lenp, const u_char *data, size_t datalen, 233 u_int compat, const char *pin) 234{ 235 int oerrno, r = SSH_ERR_INTERNAL_ERROR; 236 struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL; 237 238 *sigp = NULL; 239 *lenp = 0; 240 241 if ((kbuf = sshbuf_new()) == NULL || 242 (req = sshbuf_new()) == NULL) { 243 r = SSH_ERR_ALLOC_FAIL; 244 goto out; 245 } 246 247 if ((r = sshkey_private_serialize(key, kbuf)) != 0) { 248 error_fr(r, "encode key"); 249 goto out; 250 } 251 if ((r = sshbuf_put_stringb(req, kbuf)) != 0 || 252 (r = sshbuf_put_cstring(req, provider)) != 0 || 253 (r = sshbuf_put_string(req, data, datalen)) != 0 || 254 (r = sshbuf_put_cstring(req, NULL)) != 0 || /* alg */ 255 (r = sshbuf_put_u32(req, compat)) != 0 || 256 (r = sshbuf_put_cstring(req, pin)) != 0) { 257 error_fr(r, "compose"); 258 goto out; 259 } 260 261 if ((r = client_converse(req, &resp, SSH_SK_HELPER_SIGN)) != 0) 262 goto out; 263 264 if ((r = sshbuf_get_string(resp, sigp, lenp)) != 0) { 265 error_fr(r, "parse signature"); 266 r = SSH_ERR_INVALID_FORMAT; 267 goto out; 268 } 269 if (sshbuf_len(resp) != 0) { 270 error_f("trailing data in response"); 271 r = SSH_ERR_INVALID_FORMAT; 272 goto out; 273 } 274 /* success */ 275 r = 0; 276 out: 277 oerrno = errno; 278 if (r != 0) { 279 freezero(*sigp, *lenp); 280 *sigp = NULL; 281 *lenp = 0; 282 } 283 sshbuf_free(kbuf); 284 sshbuf_free(req); 285 sshbuf_free(resp); 286 errno = oerrno; 287 return r; 288} 289 290int 291sshsk_enroll(int type, const char *provider_path, const char *device, 292 const char *application, const char *userid, uint8_t flags, 293 const char *pin, struct sshbuf *challenge_buf, 294 struct sshkey **keyp, struct sshbuf *attest) 295{ 296 int oerrno, r = SSH_ERR_INTERNAL_ERROR; 297 struct sshbuf *kbuf = NULL, *abuf = NULL, *req = NULL, *resp = NULL; 298 struct sshkey *key = NULL; 299 300 *keyp = NULL; 301 if (attest != NULL) 302 sshbuf_reset(attest); 303 304 if (type < 0) 305 return SSH_ERR_INVALID_ARGUMENT; 306 307 if ((abuf = sshbuf_new()) == NULL || 308 (kbuf = sshbuf_new()) == NULL || 309 (req = sshbuf_new()) == NULL) { 310 r = SSH_ERR_ALLOC_FAIL; 311 goto out; 312 } 313 314 if ((r = sshbuf_put_u32(req, (u_int)type)) != 0 || 315 (r = sshbuf_put_cstring(req, provider_path)) != 0 || 316 (r = sshbuf_put_cstring(req, device)) != 0 || 317 (r = sshbuf_put_cstring(req, application)) != 0 || 318 (r = sshbuf_put_cstring(req, userid)) != 0 || 319 (r = sshbuf_put_u8(req, flags)) != 0 || 320 (r = sshbuf_put_cstring(req, pin)) != 0 || 321 (r = sshbuf_put_stringb(req, challenge_buf)) != 0) { 322 error_fr(r, "compose"); 323 goto out; 324 } 325 326 if ((r = client_converse(req, &resp, SSH_SK_HELPER_ENROLL)) != 0) 327 goto out; 328 329 if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 || 330 (r = sshbuf_get_stringb(resp, abuf)) != 0) { 331 error_fr(r, "parse"); 332 r = SSH_ERR_INVALID_FORMAT; 333 goto out; 334 } 335 if (sshbuf_len(resp) != 0) { 336 error_f("trailing data in response"); 337 r = SSH_ERR_INVALID_FORMAT; 338 goto out; 339 } 340 if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) { 341 error_fr(r, "encode"); 342 goto out; 343 } 344 if (attest != NULL && (r = sshbuf_putb(attest, abuf)) != 0) { 345 error_fr(r, "encode attestation information"); 346 goto out; 347 } 348 349 /* success */ 350 r = 0; 351 *keyp = key; 352 key = NULL; 353 out: 354 oerrno = errno; 355 sshkey_free(key); 356 sshbuf_free(kbuf); 357 sshbuf_free(abuf); 358 sshbuf_free(req); 359 sshbuf_free(resp); 360 errno = oerrno; 361 return r; 362} 363 364static void 365sshsk_free_resident_key(struct sshsk_resident_key *srk) 366{ 367 if (srk == NULL) 368 return; 369 sshkey_free(srk->key); 370 freezero(srk->user_id, srk->user_id_len); 371 free(srk); 372} 373 374 375void 376sshsk_free_resident_keys(struct sshsk_resident_key **srks, size_t nsrks) 377{ 378 size_t i; 379 380 if (srks == NULL || nsrks == 0) 381 return; 382 383 for (i = 0; i < nsrks; i++) 384 sshsk_free_resident_key(srks[i]); 385 free(srks); 386} 387 388int 389sshsk_load_resident(const char *provider_path, const char *device, 390 const char *pin, u_int flags, struct sshsk_resident_key ***srksp, 391 size_t *nsrksp) 392{ 393 int oerrno, r = SSH_ERR_INTERNAL_ERROR; 394 struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL; 395 struct sshkey *key = NULL; 396 struct sshsk_resident_key *srk = NULL, **srks = NULL, **tmp; 397 u_char *userid = NULL; 398 size_t userid_len = 0, nsrks = 0; 399 400 *srksp = NULL; 401 *nsrksp = 0; 402 403 if ((kbuf = sshbuf_new()) == NULL || 404 (req = sshbuf_new()) == NULL) { 405 r = SSH_ERR_ALLOC_FAIL; 406 goto out; 407 } 408 409 if ((r = sshbuf_put_cstring(req, provider_path)) != 0 || 410 (r = sshbuf_put_cstring(req, device)) != 0 || 411 (r = sshbuf_put_cstring(req, pin)) != 0 || 412 (r = sshbuf_put_u32(req, flags)) != 0) { 413 error_fr(r, "compose"); 414 goto out; 415 } 416 417 if ((r = client_converse(req, &resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0) 418 goto out; 419 420 while (sshbuf_len(resp) != 0) { 421 /* key, comment, user_id */ 422 if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 || 423 (r = sshbuf_get_cstring(resp, NULL, NULL)) != 0 || 424 (r = sshbuf_get_string(resp, &userid, &userid_len)) != 0) { 425 error_fr(r, "parse"); 426 r = SSH_ERR_INVALID_FORMAT; 427 goto out; 428 } 429 if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) { 430 error_fr(r, "decode key"); 431 goto out; 432 } 433 if ((srk = calloc(1, sizeof(*srk))) == NULL) { 434 error_f("calloc failed"); 435 goto out; 436 } 437 srk->key = key; 438 key = NULL; 439 srk->user_id = userid; 440 srk->user_id_len = userid_len; 441 userid = NULL; 442 userid_len = 0; 443 if ((tmp = recallocarray(srks, nsrks, nsrks + 1, 444 sizeof(*srks))) == NULL) { 445 error_f("recallocarray keys failed"); 446 goto out; 447 } 448 debug_f("srks[%zu]: %s %s uidlen %zu", nsrks, 449 sshkey_type(srk->key), srk->key->sk_application, 450 srk->user_id_len); 451 srks = tmp; 452 srks[nsrks++] = srk; 453 srk = NULL; 454 } 455 456 /* success */ 457 r = 0; 458 *srksp = srks; 459 *nsrksp = nsrks; 460 srks = NULL; 461 nsrks = 0; 462 out: 463 oerrno = errno; 464 sshsk_free_resident_key(srk); 465 sshsk_free_resident_keys(srks, nsrks); 466 freezero(userid, userid_len); 467 sshkey_free(key); 468 sshbuf_free(kbuf); 469 sshbuf_free(req); 470 sshbuf_free(resp); 471 errno = oerrno; 472 return r; 473} 474