1 /* $OpenBSD: ssh-sk-helper.c,v 1.11 2020/10/18 11:32:02 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 sshkey **keys = NULL; 220 size_t nkeys = 0, i; 221 222 if ((kbuf = sshbuf_new()) == NULL) 223 fatal("%s: sshbuf_new failed", __progname); 224 225 if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 226 (r = sshbuf_get_cstring(req, &device, NULL)) != 0 || 227 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0) 228 fatal_r(r, "%s: parse", __progname); 229 if (sshbuf_len(req) != 0) 230 fatal("%s: trailing data in request", __progname); 231 232 null_empty(&device); 233 null_empty(&pin); 234 235 if ((r = sshsk_load_resident(provider, device, pin, 236 &keys, &nkeys)) != 0) { 237 resp = reply_error(r, " sshsk_load_resident failed: %s", 238 ssh_err(r)); 239 goto out; 240 } 241 242 if ((resp = sshbuf_new()) == NULL) 243 fatal("%s: sshbuf_new failed", __progname); 244 245 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0) 246 fatal_r(r, "%s: compose", __progname); 247 248 for (i = 0; i < nkeys; i++) { 249 debug_f("key %zu %s %s", i, sshkey_type(keys[i]), 250 keys[i]->sk_application); 251 sshbuf_reset(kbuf); 252 if ((r = sshkey_private_serialize(keys[i], kbuf)) != 0) 253 fatal_r(r, "%s: encode key", __progname); 254 if ((r = sshbuf_put_stringb(resp, kbuf)) != 0 || 255 (r = sshbuf_put_cstring(resp, "")) != 0) /* comment */ 256 fatal_r(r, "%s: compose key", __progname); 257 } 258 259 out: 260 for (i = 0; i < nkeys; i++) 261 sshkey_free(keys[i]); 262 free(keys); 263 sshbuf_free(kbuf); 264 free(provider); 265 if (pin != NULL) 266 freezero(pin, strlen(pin)); 267 return resp; 268 } 269 270 int 271 main(int argc, char **argv) 272 { 273 SyslogFacility log_facility = SYSLOG_FACILITY_AUTH; 274 LogLevel log_level = SYSLOG_LEVEL_ERROR; 275 struct sshbuf *req, *resp; 276 int in, out, ch, r, vflag = 0; 277 u_int rtype, ll = 0; 278 uint8_t version, log_stderr = 0; 279 280 sanitise_stdfd(); 281 log_init(__progname, log_level, log_facility, log_stderr); 282 283 while ((ch = getopt(argc, argv, "v")) != -1) { 284 switch (ch) { 285 case 'v': 286 vflag = 1; 287 if (log_level == SYSLOG_LEVEL_ERROR) 288 log_level = SYSLOG_LEVEL_DEBUG1; 289 else if (log_level < SYSLOG_LEVEL_DEBUG3) 290 log_level++; 291 break; 292 default: 293 fprintf(stderr, "usage: %s [-v]\n", __progname); 294 exit(1); 295 } 296 } 297 log_init(__progname, log_level, log_facility, vflag); 298 299 /* 300 * Rearrange our file descriptors a little; we don't trust the 301 * providers not to fiddle with stdin/out. 302 */ 303 closefrom(STDERR_FILENO + 1); 304 if ((in = dup(STDIN_FILENO)) == -1 || (out = dup(STDOUT_FILENO)) == -1) 305 fatal("%s: dup: %s", __progname, strerror(errno)); 306 close(STDIN_FILENO); 307 close(STDOUT_FILENO); 308 sanitise_stdfd(); /* resets to /dev/null */ 309 310 if ((req = sshbuf_new()) == NULL) 311 fatal("%s: sshbuf_new failed", __progname); 312 if (ssh_msg_recv(in, req) < 0) 313 fatal("ssh_msg_recv failed"); 314 close(in); 315 debug_f("received message len %zu", sshbuf_len(req)); 316 317 if ((r = sshbuf_get_u8(req, &version)) != 0) 318 fatal_r(r, "%s: parse version", __progname); 319 if (version != SSH_SK_HELPER_VERSION) { 320 fatal("unsupported version: received %d, expected %d", 321 version, SSH_SK_HELPER_VERSION); 322 } 323 324 if ((r = sshbuf_get_u32(req, &rtype)) != 0 || 325 (r = sshbuf_get_u8(req, &log_stderr)) != 0 || 326 (r = sshbuf_get_u32(req, &ll)) != 0) 327 fatal_r(r, "%s: parse", __progname); 328 329 if (!vflag && log_level_name((LogLevel)ll) != NULL) 330 log_init(__progname, (LogLevel)ll, log_facility, log_stderr); 331 332 switch (rtype) { 333 case SSH_SK_HELPER_SIGN: 334 resp = process_sign(req); 335 break; 336 case SSH_SK_HELPER_ENROLL: 337 resp = process_enroll(req); 338 break; 339 case SSH_SK_HELPER_LOAD_RESIDENT: 340 resp = process_load_resident(req); 341 break; 342 default: 343 fatal("%s: unsupported request type %u", __progname, rtype); 344 } 345 sshbuf_free(req); 346 debug_f("reply len %zu", sshbuf_len(resp)); 347 348 if (ssh_msg_send(out, SSH_SK_HELPER_VERSION, resp) == -1) 349 fatal("ssh_msg_send failed"); 350 sshbuf_free(resp); 351 close(out); 352 353 return (0); 354 } 355 #else /* ENABLE_SK */ 356 #include <stdio.h> 357 358 int 359 main(int argc, char **argv) 360 { 361 fprintf(stderr, "ssh-sk-helper: disabled at compile time\n"); 362 return -1; 363 } 364 #endif /* ENABLE_SK */ 365