1 /* $OpenBSD: ssh-sk-helper.c,v 1.12 2021/10/28 02:54:18 djm Exp $ */ 2 /* 3 * Copyright (c) 2019 Google LLC 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 /* 19 * This is a tiny program used to isolate the address space used for 20 * security key middleware signing operations from ssh-agent. It is similar 21 * to ssh-pkcs11-helper.c but considerably simpler as the operations for 22 * security keys are stateless. 23 * 24 * Please crank SSH_SK_HELPER_VERSION in sshkey.h for any incompatible 25 * protocol changes. 26 */ 27 28 #include "includes.h" 29 30 #include <limits.h> 31 #include <stdarg.h> 32 #include <stdio.h> 33 #include <stdlib.h> 34 #include <string.h> 35 #include <unistd.h> 36 #include <errno.h> 37 38 #include "xmalloc.h" 39 #include "log.h" 40 #include "sshkey.h" 41 #include "authfd.h" 42 #include "misc.h" 43 #include "sshbuf.h" 44 #include "msg.h" 45 #include "uidswap.h" 46 #include "sshkey.h" 47 #include "ssherr.h" 48 #include "ssh-sk.h" 49 50 #ifdef ENABLE_SK 51 extern char *__progname; 52 53 static struct sshbuf *reply_error(int r, char *fmt, ...) 54 __attribute__((__format__ (printf, 2, 3))); 55 56 static struct sshbuf * 57 reply_error(int r, char *fmt, ...) 58 { 59 char *msg; 60 va_list ap; 61 struct sshbuf *resp; 62 63 va_start(ap, fmt); 64 xvasprintf(&msg, fmt, ap); 65 va_end(ap); 66 debug("%s: %s", __progname, msg); 67 free(msg); 68 69 if (r >= 0) 70 fatal_f("invalid error code %d", r); 71 72 if ((resp = sshbuf_new()) == NULL) 73 fatal("%s: sshbuf_new failed", __progname); 74 if (sshbuf_put_u32(resp, SSH_SK_HELPER_ERROR) != 0 || 75 sshbuf_put_u32(resp, (u_int)-r) != 0) 76 fatal("%s: buffer error", __progname); 77 return resp; 78 } 79 80 /* If the specified string is zero length, then free it and replace with NULL */ 81 static void 82 null_empty(char **s) 83 { 84 if (s == NULL || *s == NULL || **s != '\0') 85 return; 86 87 free(*s); 88 *s = NULL; 89 } 90 91 static struct sshbuf * 92 process_sign(struct sshbuf *req) 93 { 94 int r = SSH_ERR_INTERNAL_ERROR; 95 struct sshbuf *resp, *kbuf; 96 struct sshkey *key = NULL; 97 uint32_t compat; 98 const u_char *message; 99 u_char *sig = NULL; 100 size_t msglen, siglen = 0; 101 char *provider = NULL, *pin = NULL; 102 103 if ((r = sshbuf_froms(req, &kbuf)) != 0 || 104 (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 105 (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 || 106 (r = sshbuf_get_cstring(req, NULL, NULL)) != 0 || /* alg */ 107 (r = sshbuf_get_u32(req, &compat)) != 0 || 108 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0) 109 fatal_r(r, "%s: parse", __progname); 110 if (sshbuf_len(req) != 0) 111 fatal("%s: trailing data in request", __progname); 112 113 if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) 114 fatal_r(r, "%s: Unable to parse private key", __progname); 115 if (!sshkey_is_sk(key)) { 116 fatal("%s: Unsupported key type %s", 117 __progname, sshkey_ssh_name(key)); 118 } 119 120 debug_f("ready to sign with key %s, provider %s: " 121 "msg len %zu, compat 0x%lx", sshkey_type(key), 122 provider, msglen, (u_long)compat); 123 124 null_empty(&pin); 125 126 if ((r = sshsk_sign(provider, key, &sig, &siglen, 127 message, msglen, compat, pin)) != 0) { 128 resp = reply_error(r, "Signing failed: %s", ssh_err(r)); 129 goto out; 130 } 131 132 if ((resp = sshbuf_new()) == NULL) 133 fatal("%s: sshbuf_new failed", __progname); 134 135 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_SIGN)) != 0 || 136 (r = sshbuf_put_string(resp, sig, siglen)) != 0) 137 fatal_r(r, "%s: compose", __progname); 138 out: 139 sshkey_free(key); 140 sshbuf_free(kbuf); 141 free(provider); 142 if (sig != NULL) 143 freezero(sig, siglen); 144 if (pin != NULL) 145 freezero(pin, strlen(pin)); 146 return resp; 147 } 148 149 static struct sshbuf * 150 process_enroll(struct sshbuf *req) 151 { 152 int r; 153 u_int type; 154 char *provider, *application, *pin, *device, *userid; 155 uint8_t flags; 156 struct sshbuf *challenge, *attest, *kbuf, *resp; 157 struct sshkey *key; 158 159 if ((attest = sshbuf_new()) == NULL || 160 (kbuf = sshbuf_new()) == NULL) 161 fatal("%s: sshbuf_new failed", __progname); 162 163 if ((r = sshbuf_get_u32(req, &type)) != 0 || 164 (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 165 (r = sshbuf_get_cstring(req, &device, NULL)) != 0 || 166 (r = sshbuf_get_cstring(req, &application, NULL)) != 0 || 167 (r = sshbuf_get_cstring(req, &userid, NULL)) != 0 || 168 (r = sshbuf_get_u8(req, &flags)) != 0 || 169 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 || 170 (r = sshbuf_froms(req, &challenge)) != 0) 171 fatal_r(r, "%s: parse", __progname); 172 if (sshbuf_len(req) != 0) 173 fatal("%s: trailing data in request", __progname); 174 175 if (type > INT_MAX) 176 fatal("%s: bad type %u", __progname, type); 177 if (sshbuf_len(challenge) == 0) { 178 sshbuf_free(challenge); 179 challenge = NULL; 180 } 181 null_empty(&device); 182 null_empty(&userid); 183 null_empty(&pin); 184 185 if ((r = sshsk_enroll((int)type, provider, device, application, userid, 186 flags, pin, challenge, &key, attest)) != 0) { 187 resp = reply_error(r, "Enrollment failed: %s", ssh_err(r)); 188 goto out; 189 } 190 191 if ((resp = sshbuf_new()) == NULL) 192 fatal("%s: sshbuf_new failed", __progname); 193 if ((r = sshkey_private_serialize(key, kbuf)) != 0) 194 fatal_r(r, "%s: encode key", __progname); 195 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_ENROLL)) != 0 || 196 (r = sshbuf_put_stringb(resp, kbuf)) != 0 || 197 (r = sshbuf_put_stringb(resp, attest)) != 0) 198 fatal_r(r, "%s: compose", __progname); 199 200 out: 201 sshkey_free(key); 202 sshbuf_free(kbuf); 203 sshbuf_free(attest); 204 sshbuf_free(challenge); 205 free(provider); 206 free(application); 207 if (pin != NULL) 208 freezero(pin, strlen(pin)); 209 210 return resp; 211 } 212 213 static struct sshbuf * 214 process_load_resident(struct sshbuf *req) 215 { 216 int r; 217 char *provider, *pin, *device; 218 struct sshbuf *kbuf, *resp; 219 struct sshsk_resident_key **srks = NULL; 220 size_t nsrks = 0, i; 221 u_int flags; 222 223 if ((kbuf = sshbuf_new()) == NULL) 224 fatal("%s: sshbuf_new failed", __progname); 225 226 if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 227 (r = sshbuf_get_cstring(req, &device, NULL)) != 0 || 228 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 || 229 (r = sshbuf_get_u32(req, &flags)) != 0) 230 fatal_r(r, "%s: parse", __progname); 231 if (sshbuf_len(req) != 0) 232 fatal("%s: trailing data in request", __progname); 233 234 null_empty(&device); 235 null_empty(&pin); 236 237 if ((r = sshsk_load_resident(provider, device, pin, flags, 238 &srks, &nsrks)) != 0) { 239 resp = reply_error(r, "sshsk_load_resident failed: %s", 240 ssh_err(r)); 241 goto out; 242 } 243 244 if ((resp = sshbuf_new()) == NULL) 245 fatal("%s: sshbuf_new failed", __progname); 246 247 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0) 248 fatal_r(r, "%s: compose", __progname); 249 250 for (i = 0; i < nsrks; i++) { 251 debug_f("key %zu %s %s uidlen %zu", i, 252 sshkey_type(srks[i]->key), srks[i]->key->sk_application, 253 srks[i]->user_id_len); 254 sshbuf_reset(kbuf); 255 if ((r = sshkey_private_serialize(srks[i]->key, kbuf)) != 0) 256 fatal_r(r, "%s: encode key", __progname); 257 if ((r = sshbuf_put_stringb(resp, kbuf)) != 0 || 258 (r = sshbuf_put_cstring(resp, "")) != 0 || /* comment */ 259 (r = sshbuf_put_string(resp, srks[i]->user_id, 260 srks[i]->user_id_len)) != 0) 261 fatal_r(r, "%s: compose key", __progname); 262 } 263 264 out: 265 sshsk_free_resident_keys(srks, nsrks); 266 sshbuf_free(kbuf); 267 free(provider); 268 if (pin != NULL) 269 freezero(pin, strlen(pin)); 270 return resp; 271 } 272 273 int 274 main(int argc, char **argv) 275 { 276 SyslogFacility log_facility = SYSLOG_FACILITY_AUTH; 277 LogLevel log_level = SYSLOG_LEVEL_ERROR; 278 struct sshbuf *req, *resp; 279 int in, out, ch, r, vflag = 0; 280 u_int rtype, ll = 0; 281 uint8_t version, log_stderr = 0; 282 283 sanitise_stdfd(); 284 log_init(__progname, log_level, log_facility, log_stderr); 285 286 while ((ch = getopt(argc, argv, "v")) != -1) { 287 switch (ch) { 288 case 'v': 289 vflag = 1; 290 if (log_level == SYSLOG_LEVEL_ERROR) 291 log_level = SYSLOG_LEVEL_DEBUG1; 292 else if (log_level < SYSLOG_LEVEL_DEBUG3) 293 log_level++; 294 break; 295 default: 296 fprintf(stderr, "usage: %s [-v]\n", __progname); 297 exit(1); 298 } 299 } 300 log_init(__progname, log_level, log_facility, vflag); 301 302 /* 303 * Rearrange our file descriptors a little; we don't trust the 304 * providers not to fiddle with stdin/out. 305 */ 306 closefrom(STDERR_FILENO + 1); 307 if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1) 308 fatal("%s: dup: %s", __progname, strerror(errno)); 309 close(STDIN_FILENO); 310 close(STDOUT_FILENO); 311 sanitise_stdfd(); /* resets to /dev/null */ 312 313 if ((req = sshbuf_new()) == NULL) 314 fatal("%s: sshbuf_new failed", __progname); 315 if (ssh_msg_recv(in, req) < 0) 316 fatal("ssh_msg_recv failed"); 317 close(in); 318 debug_f("received message len %zu", sshbuf_len(req)); 319 320 if ((r = sshbuf_get_u8(req, &version)) != 0) 321 fatal_r(r, "%s: parse version", __progname); 322 if (version != SSH_SK_HELPER_VERSION) { 323 fatal("unsupported version: received %d, expected %d", 324 version, SSH_SK_HELPER_VERSION); 325 } 326 327 if ((r = sshbuf_get_u32(req, &rtype)) != 0 || 328 (r = sshbuf_get_u8(req, &log_stderr)) != 0 || 329 (r = sshbuf_get_u32(req, &ll)) != 0) 330 fatal_r(r, "%s: parse", __progname); 331 332 if (!vflag && log_level_name((LogLevel)ll) != NULL) 333 log_init(__progname, (LogLevel)ll, log_facility, log_stderr); 334 335 switch (rtype) { 336 case SSH_SK_HELPER_SIGN: 337 resp = process_sign(req); 338 break; 339 case SSH_SK_HELPER_ENROLL: 340 resp = process_enroll(req); 341 break; 342 case SSH_SK_HELPER_LOAD_RESIDENT: 343 resp = process_load_resident(req); 344 break; 345 default: 346 fatal("%s: unsupported request type %u", __progname, rtype); 347 } 348 sshbuf_free(req); 349 debug_f("reply len %zu", sshbuf_len(resp)); 350 351 if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1) 352 fatal("ssh_msg_send failed"); 353 sshbuf_free(resp); 354 close(out); 355 356 return (0); 357 } 358 #else /* ENABLE_SK */ 359 #include <stdio.h> 360 361 int 362 main(int argc, char **argv) 363 { 364 fprintf(stderr, "ssh-sk-helper: disabled at compile time\n"); 365 return -1; 366 } 367 #endif /* ENABLE_SK */ 368