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 <limits.h> 29 #include <stdarg.h> 30 #include <stdio.h> 31 #include <stdlib.h> 32 #include <string.h> 33 #include <unistd.h> 34 #include <errno.h> 35 36 #include "xmalloc.h" 37 #include "log.h" 38 #include "sshkey.h" 39 #include "authfd.h" 40 #include "misc.h" 41 #include "sshbuf.h" 42 #include "msg.h" 43 #include "uidswap.h" 44 #include "sshkey.h" 45 #include "ssherr.h" 46 #include "ssh-sk.h" 47 48 extern char *__progname; 49 50 static struct sshbuf *reply_error(int r, char *fmt, ...) 51 __attribute__((__format__ (printf, 2, 3))); 52 53 static struct sshbuf * 54 reply_error(int r, char *fmt, ...) 55 { 56 char *msg; 57 va_list ap; 58 struct sshbuf *resp; 59 60 va_start(ap, fmt); 61 xvasprintf(&msg, fmt, ap); 62 va_end(ap); 63 debug("%s: %s", __progname, msg); 64 free(msg); 65 66 if (r >= 0) 67 fatal_f("invalid error code %d", r); 68 69 if ((resp = sshbuf_new()) == NULL) 70 fatal("%s: sshbuf_new failed", __progname); 71 if (sshbuf_put_u32(resp, SSH_SK_HELPER_ERROR) != 0 || 72 sshbuf_put_u32(resp, (u_int)-r) != 0) 73 fatal("%s: buffer error", __progname); 74 return resp; 75 } 76 77 /* If the specified string is zero length, then free it and replace with NULL */ 78 static void 79 null_empty(char **s) 80 { 81 if (s == NULL || *s == NULL || **s != '\0') 82 return; 83 84 free(*s); 85 *s = NULL; 86 } 87 88 static struct sshbuf * 89 process_sign(struct sshbuf *req) 90 { 91 int r = SSH_ERR_INTERNAL_ERROR; 92 struct sshbuf *resp, *kbuf; 93 struct sshkey *key = NULL; 94 uint32_t compat; 95 const u_char *message; 96 u_char *sig = NULL; 97 size_t msglen, siglen = 0; 98 char *provider = NULL, *pin = NULL; 99 100 if ((r = sshbuf_froms(req, &kbuf)) != 0 || 101 (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 102 (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 || 103 (r = sshbuf_get_cstring(req, NULL, NULL)) != 0 || /* alg */ 104 (r = sshbuf_get_u32(req, &compat)) != 0 || 105 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0) 106 fatal_r(r, "%s: parse", __progname); 107 if (sshbuf_len(req) != 0) 108 fatal("%s: trailing data in request", __progname); 109 110 if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) 111 fatal_r(r, "%s: Unable to parse private key", __progname); 112 if (!sshkey_is_sk(key)) { 113 fatal("%s: Unsupported key type %s", 114 __progname, sshkey_ssh_name(key)); 115 } 116 117 debug_f("ready to sign with key %s, provider %s: " 118 "msg len %zu, compat 0x%lx", sshkey_type(key), 119 provider, msglen, (u_long)compat); 120 121 null_empty(&pin); 122 123 if ((r = sshsk_sign(provider, key, &sig, &siglen, 124 message, msglen, compat, pin)) != 0) { 125 resp = reply_error(r, "Signing failed: %s", ssh_err(r)); 126 goto out; 127 } 128 129 if ((resp = sshbuf_new()) == NULL) 130 fatal("%s: sshbuf_new failed", __progname); 131 132 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_SIGN)) != 0 || 133 (r = sshbuf_put_string(resp, sig, siglen)) != 0) 134 fatal_r(r, "%s: compose", __progname); 135 out: 136 sshkey_free(key); 137 sshbuf_free(kbuf); 138 free(provider); 139 if (sig != NULL) 140 freezero(sig, siglen); 141 if (pin != NULL) 142 freezero(pin, strlen(pin)); 143 return resp; 144 } 145 146 static struct sshbuf * 147 process_enroll(struct sshbuf *req) 148 { 149 int r; 150 u_int type; 151 char *provider, *application, *pin, *device, *userid; 152 uint8_t flags; 153 struct sshbuf *challenge, *attest, *kbuf, *resp; 154 struct sshkey *key; 155 156 if ((attest = sshbuf_new()) == NULL || 157 (kbuf = sshbuf_new()) == NULL) 158 fatal("%s: sshbuf_new failed", __progname); 159 160 if ((r = sshbuf_get_u32(req, &type)) != 0 || 161 (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 162 (r = sshbuf_get_cstring(req, &device, NULL)) != 0 || 163 (r = sshbuf_get_cstring(req, &application, NULL)) != 0 || 164 (r = sshbuf_get_cstring(req, &userid, NULL)) != 0 || 165 (r = sshbuf_get_u8(req, &flags)) != 0 || 166 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 || 167 (r = sshbuf_froms(req, &challenge)) != 0) 168 fatal_r(r, "%s: parse", __progname); 169 if (sshbuf_len(req) != 0) 170 fatal("%s: trailing data in request", __progname); 171 172 if (type > INT_MAX) 173 fatal("%s: bad type %u", __progname, type); 174 if (sshbuf_len(challenge) == 0) { 175 sshbuf_free(challenge); 176 challenge = NULL; 177 } 178 null_empty(&device); 179 null_empty(&userid); 180 null_empty(&pin); 181 182 if ((r = sshsk_enroll((int)type, provider, device, application, userid, 183 flags, pin, challenge, &key, attest)) != 0) { 184 resp = reply_error(r, "Enrollment failed: %s", ssh_err(r)); 185 goto out; 186 } 187 188 if ((resp = sshbuf_new()) == NULL) 189 fatal("%s: sshbuf_new failed", __progname); 190 if ((r = sshkey_private_serialize(key, kbuf)) != 0) 191 fatal_r(r, "%s: encode key", __progname); 192 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_ENROLL)) != 0 || 193 (r = sshbuf_put_stringb(resp, kbuf)) != 0 || 194 (r = sshbuf_put_stringb(resp, attest)) != 0) 195 fatal_r(r, "%s: compose", __progname); 196 197 out: 198 sshkey_free(key); 199 sshbuf_free(kbuf); 200 sshbuf_free(attest); 201 sshbuf_free(challenge); 202 free(provider); 203 free(application); 204 if (pin != NULL) 205 freezero(pin, strlen(pin)); 206 207 return resp; 208 } 209 210 static struct sshbuf * 211 process_load_resident(struct sshbuf *req) 212 { 213 int r; 214 char *provider, *pin, *device; 215 struct sshbuf *kbuf, *resp; 216 struct sshsk_resident_key **srks = NULL; 217 size_t nsrks = 0, i; 218 u_int flags; 219 220 if ((kbuf = sshbuf_new()) == NULL) 221 fatal("%s: sshbuf_new failed", __progname); 222 223 if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 || 224 (r = sshbuf_get_cstring(req, &device, NULL)) != 0 || 225 (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 || 226 (r = sshbuf_get_u32(req, &flags)) != 0) 227 fatal_r(r, "%s: parse", __progname); 228 if (sshbuf_len(req) != 0) 229 fatal("%s: trailing data in request", __progname); 230 231 null_empty(&device); 232 null_empty(&pin); 233 234 if ((r = sshsk_load_resident(provider, device, pin, flags, 235 &srks, &nsrks)) != 0) { 236 resp = reply_error(r, "sshsk_load_resident failed: %s", 237 ssh_err(r)); 238 goto out; 239 } 240 241 if ((resp = sshbuf_new()) == NULL) 242 fatal("%s: sshbuf_new failed", __progname); 243 244 if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0) 245 fatal_r(r, "%s: compose", __progname); 246 247 for (i = 0; i < nsrks; i++) { 248 debug_f("key %zu %s %s uidlen %zu", i, 249 sshkey_type(srks[i]->key), srks[i]->key->sk_application, 250 srks[i]->user_id_len); 251 sshbuf_reset(kbuf); 252 if ((r = sshkey_private_serialize(srks[i]->key, 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 (r = sshbuf_put_string(resp, srks[i]->user_id, 257 srks[i]->user_id_len)) != 0) 258 fatal_r(r, "%s: compose key", __progname); 259 } 260 261 out: 262 sshsk_free_resident_keys(srks, nsrks); 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