1 /* $OpenBSD: auth2-pubkey.c,v 1.22 2010/03/10 23:27:17 djm Exp $ */ 2 /* 3 * Copyright (c) 2000 Markus Friedl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 #include "includes.h" 27 28 #include <sys/types.h> 29 #include <sys/stat.h> 30 31 #include <fcntl.h> 32 #include <pwd.h> 33 #include <stdio.h> 34 #include <stdarg.h> 35 #include <string.h> 36 #include <time.h> 37 #include <unistd.h> 38 39 #include "xmalloc.h" 40 #include "ssh.h" 41 #include "ssh2.h" 42 #include "packet.h" 43 #include "buffer.h" 44 #include "log.h" 45 #include "servconf.h" 46 #include "compat.h" 47 #include "key.h" 48 #include "hostfile.h" 49 #include "auth.h" 50 #include "pathnames.h" 51 #include "uidswap.h" 52 #include "auth-options.h" 53 #include "canohost.h" 54 #ifdef GSSAPI 55 #include "ssh-gss.h" 56 #endif 57 #include "monitor_wrap.h" 58 #include "misc.h" 59 #include "authfile.h" 60 61 /* import */ 62 extern ServerOptions options; 63 extern u_char *session_id2; 64 extern u_int session_id2_len; 65 66 static int 67 userauth_pubkey(Authctxt *authctxt) 68 { 69 Buffer b; 70 Key *key = NULL; 71 char *pkalg; 72 u_char *pkblob, *sig; 73 u_int alen, blen, slen; 74 int have_sig, pktype; 75 int authenticated = 0; 76 77 if (!authctxt->valid) { 78 debug2("userauth_pubkey: disabled because of invalid user"); 79 return 0; 80 } 81 have_sig = packet_get_char(); 82 if (datafellows & SSH_BUG_PKAUTH) { 83 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 84 /* no explicit pkalg given */ 85 pkblob = packet_get_string(&blen); 86 buffer_init(&b); 87 buffer_append(&b, pkblob, blen); 88 /* so we have to extract the pkalg from the pkblob */ 89 pkalg = buffer_get_string(&b, &alen); 90 buffer_free(&b); 91 } else { 92 pkalg = packet_get_string(&alen); 93 pkblob = packet_get_string(&blen); 94 } 95 pktype = key_type_from_name(pkalg); 96 if (pktype == KEY_UNSPEC) { 97 /* this is perfectly legal */ 98 logit("userauth_pubkey: unsupported public key algorithm: %s", 99 pkalg); 100 goto done; 101 } 102 key = key_from_blob(pkblob, blen); 103 if (key == NULL) { 104 error("userauth_pubkey: cannot decode key: %s", pkalg); 105 goto done; 106 } 107 if (key->type != pktype) { 108 error("userauth_pubkey: type mismatch for decoded key " 109 "(received %d, expected %d)", key->type, pktype); 110 goto done; 111 } 112 if (have_sig) { 113 sig = packet_get_string(&slen); 114 packet_check_eom(); 115 buffer_init(&b); 116 if (datafellows & SSH_OLD_SESSIONID) { 117 buffer_append(&b, session_id2, session_id2_len); 118 } else { 119 buffer_put_string(&b, session_id2, session_id2_len); 120 } 121 /* reconstruct packet */ 122 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 123 buffer_put_cstring(&b, authctxt->user); 124 buffer_put_cstring(&b, 125 datafellows & SSH_BUG_PKSERVICE ? 126 "ssh-userauth" : 127 authctxt->service); 128 if (datafellows & SSH_BUG_PKAUTH) { 129 buffer_put_char(&b, have_sig); 130 } else { 131 buffer_put_cstring(&b, "publickey"); 132 buffer_put_char(&b, have_sig); 133 buffer_put_cstring(&b, pkalg); 134 } 135 buffer_put_string(&b, pkblob, blen); 136 #ifdef DEBUG_PK 137 buffer_dump(&b); 138 #endif 139 /* test for correct signature */ 140 authenticated = 0; 141 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 142 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 143 buffer_len(&b))) == 1) 144 authenticated = 1; 145 buffer_free(&b); 146 xfree(sig); 147 } else { 148 debug("test whether pkalg/pkblob are acceptable"); 149 packet_check_eom(); 150 151 /* XXX fake reply and always send PK_OK ? */ 152 /* 153 * XXX this allows testing whether a user is allowed 154 * to login: if you happen to have a valid pubkey this 155 * message is sent. the message is NEVER sent at all 156 * if a user is not allowed to login. is this an 157 * issue? -markus 158 */ 159 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 160 packet_start(SSH2_MSG_USERAUTH_PK_OK); 161 packet_put_string(pkalg, alen); 162 packet_put_string(pkblob, blen); 163 packet_send(); 164 packet_write_wait(); 165 authctxt->postponed = 1; 166 } 167 } 168 if (authenticated != 1) 169 auth_clear_options(); 170 done: 171 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 172 if (key != NULL) 173 key_free(key); 174 xfree(pkalg); 175 xfree(pkblob); 176 return authenticated; 177 } 178 179 /* return 1 if user allows given key */ 180 static int 181 user_key_allowed2(struct passwd *pw, Key *key, char *file) 182 { 183 char line[SSH_MAX_PUBKEY_BYTES]; 184 const char *reason; 185 int found_key = 0; 186 FILE *f; 187 u_long linenum = 0; 188 Key *found; 189 char *fp; 190 191 /* Temporarily use the user's uid. */ 192 temporarily_use_uid(pw); 193 194 debug("trying public key file %s", file); 195 f = auth_openkeyfile(file, pw, options.strict_modes); 196 197 if (!f) { 198 restore_uid(); 199 return 0; 200 } 201 202 found_key = 0; 203 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); 204 205 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 206 char *cp, *key_options = NULL; 207 208 auth_clear_options(); 209 210 /* Skip leading whitespace, empty and comment lines. */ 211 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 212 ; 213 if (!*cp || *cp == '\n' || *cp == '#') 214 continue; 215 216 if (key_read(found, &cp) != 1) { 217 /* no key? check if there are options for this key */ 218 int quoted = 0; 219 debug2("user_key_allowed: check options: '%s'", cp); 220 key_options = cp; 221 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 222 if (*cp == '\\' && cp[1] == '"') 223 cp++; /* Skip both */ 224 else if (*cp == '"') 225 quoted = !quoted; 226 } 227 /* Skip remaining whitespace. */ 228 for (; *cp == ' ' || *cp == '\t'; cp++) 229 ; 230 if (key_read(found, &cp) != 1) { 231 debug2("user_key_allowed: advance: '%s'", cp); 232 /* still no key? advance to next line*/ 233 continue; 234 } 235 } 236 if (auth_parse_options(pw, key_options, file, linenum) != 1) 237 continue; 238 if (key->type == KEY_RSA_CERT || key->type == KEY_DSA_CERT) { 239 if (!key_is_cert_authority) 240 continue; 241 if (!key_equal(found, key->cert->signature_key)) 242 continue; 243 fp = key_fingerprint(found, SSH_FP_MD5, 244 SSH_FP_HEX); 245 debug("matching CA found: file %s, line %lu, %s %s", 246 file, linenum, key_type(found), fp); 247 if (key_cert_check_authority(key, 0, 0, pw->pw_name, 248 &reason) != 0) { 249 xfree(fp); 250 error("%s", reason); 251 auth_debug_add("%s", reason); 252 continue; 253 } 254 if (auth_cert_constraints(&key->cert->constraints, 255 pw) != 0) { 256 xfree(fp); 257 continue; 258 } 259 verbose("Accepted certificate ID \"%s\" " 260 "signed by %s CA %s via %s", key->cert->key_id, 261 key_type(found), fp, file); 262 xfree(fp); 263 found_key = 1; 264 break; 265 } else if (!key_is_cert_authority && key_equal(found, key)) { 266 found_key = 1; 267 debug("matching key found: file %s, line %lu", 268 file, linenum); 269 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 270 verbose("Found matching %s key: %s", 271 key_type(found), fp); 272 xfree(fp); 273 break; 274 } 275 } 276 restore_uid(); 277 fclose(f); 278 key_free(found); 279 if (!found_key) 280 debug2("key not found"); 281 return found_key; 282 } 283 284 /* Authenticate a certificate key against TrustedUserCAKeys */ 285 static int 286 user_cert_trusted_ca(struct passwd *pw, Key *key) 287 { 288 char *ca_fp; 289 const char *reason; 290 int ret = 0; 291 292 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) 293 return 0; 294 295 ca_fp = key_fingerprint(key->cert->signature_key, 296 SSH_FP_MD5, SSH_FP_HEX); 297 298 if (key_in_file(key->cert->signature_key, 299 options.trusted_user_ca_keys, 1) != 1) { 300 debug2("%s: CA %s %s is not listed in %s", __func__, 301 key_type(key->cert->signature_key), ca_fp, 302 options.trusted_user_ca_keys); 303 goto out; 304 } 305 if (key_cert_check_authority(key, 0, 1, pw->pw_name, &reason) != 0) { 306 error("%s", reason); 307 auth_debug_add("%s", reason); 308 goto out; 309 } 310 if (auth_cert_constraints(&key->cert->constraints, pw) != 0) 311 goto out; 312 313 verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s", 314 key->cert->key_id, key_type(key->cert->signature_key), ca_fp, 315 options.trusted_user_ca_keys); 316 ret = 1; 317 318 out: 319 if (ca_fp != NULL) 320 xfree(ca_fp); 321 return ret; 322 } 323 324 /* check whether given key is in .ssh/authorized_keys* */ 325 int 326 user_key_allowed(struct passwd *pw, Key *key) 327 { 328 int success; 329 char *file; 330 331 if (auth_key_is_revoked(key)) 332 return 0; 333 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) 334 return 0; 335 336 success = user_cert_trusted_ca(pw, key); 337 if (success) 338 return success; 339 340 file = authorized_keys_file(pw); 341 success = user_key_allowed2(pw, key, file); 342 xfree(file); 343 if (success) 344 return success; 345 346 /* try suffix "2" for backward compat, too */ 347 file = authorized_keys_file2(pw); 348 success = user_key_allowed2(pw, key, file); 349 xfree(file); 350 return success; 351 } 352 353 Authmethod method_pubkey = { 354 "publickey", 355 userauth_pubkey, 356 &options.pubkey_authentication 357 }; 358