1 /* 2 * Copyright (c) 2000 Markus Friedl. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23 */ 24 /* 25 * Copyright 2007 Sun Microsystems, Inc. All rights reserved. 26 * Use is subject to license terms. 27 */ 28 29 #include "includes.h" 30 RCSID("$OpenBSD: auth2-pubkey.c,v 1.2 2002/05/31 11:35:15 markus Exp $"); 31 32 #pragma ident "%Z%%M% %I% %E% SMI" 33 34 #include "ssh2.h" 35 #include "xmalloc.h" 36 #include "packet.h" 37 #include "buffer.h" 38 #include "log.h" 39 #include "servconf.h" 40 #include "compat.h" 41 #include "bufaux.h" 42 #include "auth.h" 43 #include "key.h" 44 #include "pathnames.h" 45 #include "uidswap.h" 46 #include "auth-options.h" 47 #include "canohost.h" 48 49 #ifdef USE_PAM 50 #include <security/pam_appl.h> 51 #include "auth-pam.h" 52 #endif /* USE_PAM */ 53 54 /* import */ 55 extern ServerOptions options; 56 extern u_char *session_id2; 57 extern int session_id2_len; 58 59 static void 60 userauth_pubkey(Authctxt *authctxt) 61 { 62 Buffer b; 63 Key *key = NULL; 64 char *pkalg; 65 u_char *pkblob, *sig; 66 u_int alen, blen, slen; 67 int have_sig, pktype; 68 int authenticated = 0; 69 70 if (!authctxt || !authctxt->method) 71 fatal("%s: missing context", __func__); 72 73 have_sig = packet_get_char(); 74 if (datafellows & SSH_BUG_PKAUTH) { 75 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 76 /* no explicit pkalg given */ 77 pkblob = packet_get_string(&blen); 78 buffer_init(&b); 79 buffer_append(&b, pkblob, blen); 80 /* so we have to extract the pkalg from the pkblob */ 81 pkalg = buffer_get_string(&b, &alen); 82 buffer_free(&b); 83 } else { 84 pkalg = packet_get_string(&alen); 85 pkblob = packet_get_string(&blen); 86 } 87 pktype = key_type_from_name(pkalg); 88 if (pktype == KEY_UNSPEC) { 89 /* this is perfectly legal */ 90 log("userauth_pubkey: unsupported public key algorithm: %s", 91 pkalg); 92 goto done; 93 } 94 key = key_from_blob(pkblob, blen); 95 if (key == NULL) { 96 error("userauth_pubkey: cannot decode key: %s", pkalg); 97 goto done; 98 } 99 if (key->type != pktype) { 100 error("userauth_pubkey: type mismatch for decoded key " 101 "(received %d, expected %d)", key->type, pktype); 102 goto done; 103 } 104 105 /* Detect and count abandonment */ 106 if (authctxt->method->method_data) { 107 Key *prev_key; 108 unsigned char *prev_pkblob; 109 int prev_blen; 110 111 /* 112 * Check for earlier test of a key that was allowed but 113 * not followed up with a pubkey req for the same pubkey 114 * and with a signature. 115 */ 116 prev_key = authctxt->method->method_data; 117 if ((prev_blen = key_to_blob(prev_key, 118 &prev_pkblob, NULL))) { 119 if (prev_blen != blen || 120 memcmp(prev_pkblob, pkblob, blen) != 0) { 121 authctxt->method->abandons++; 122 authctxt->method->attempts++; 123 } 124 } 125 key_free(prev_key); 126 authctxt->method->method_data = NULL; 127 } 128 129 if (have_sig) { 130 sig = packet_get_string(&slen); 131 packet_check_eom(); 132 buffer_init(&b); 133 if (datafellows & SSH_OLD_SESSIONID) { 134 buffer_append(&b, session_id2, session_id2_len); 135 } else { 136 buffer_put_string(&b, session_id2, session_id2_len); 137 } 138 /* reconstruct packet */ 139 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 140 buffer_put_cstring(&b, authctxt->user); 141 buffer_put_cstring(&b, 142 datafellows & SSH_BUG_PKSERVICE ? 143 "ssh-userauth" : 144 authctxt->service); 145 if (datafellows & SSH_BUG_PKAUTH) { 146 buffer_put_char(&b, have_sig); 147 } else { 148 buffer_put_cstring(&b, "publickey"); 149 buffer_put_char(&b, have_sig); 150 buffer_put_cstring(&b, pkalg); 151 } 152 buffer_put_string(&b, pkblob, blen); 153 #ifdef DEBUG_PK 154 buffer_dump(&b); 155 #endif 156 /* test for correct signature */ 157 if (user_key_allowed(authctxt->pw, key) && 158 key_verify(key, sig, slen, buffer_ptr(&b), 159 buffer_len(&b)) == 1) { 160 authenticated = 1; 161 } 162 authctxt->method->postponed = 0; 163 buffer_clear(&b); 164 xfree(sig); 165 } else { 166 debug("test whether pkalg/pkblob are acceptable"); 167 packet_check_eom(); 168 169 /* XXX fake reply and always send PK_OK ? */ 170 /* 171 * XXX this allows testing whether a user is allowed 172 * to login: if you happen to have a valid pubkey this 173 * message is sent. the message is NEVER sent at all 174 * if a user is not allowed to login. is this an 175 * issue? -markus 176 */ 177 if (user_key_allowed(authctxt->pw, key)) { 178 packet_start(SSH2_MSG_USERAUTH_PK_OK); 179 packet_put_string(pkalg, alen); 180 packet_put_string(pkblob, blen); 181 packet_send(); 182 packet_write_wait(); 183 authctxt->method->postponed = 1; 184 /* 185 * Remember key that was tried so we can 186 * correctly detect abandonment. See above. 187 */ 188 authctxt->method->method_data = (void *) key; 189 key = NULL; 190 } 191 } 192 if (authenticated != 1) 193 auth_clear_options(); 194 195 done: 196 /* 197 * XXX TODO: add config options for specifying users for whom 198 * this userauth is insufficient and what userauths may 199 * continue. 200 */ 201 #ifdef USE_PAM 202 if (authenticated) { 203 if (!do_pam_non_initial_userauth(authctxt)) 204 authenticated = 0; 205 } 206 #endif /* USE_PAM */ 207 208 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 209 if (key != NULL) 210 key_free(key); 211 xfree(pkalg); 212 xfree(pkblob); 213 #ifdef HAVE_CYGWIN 214 if (check_nt_auth(0, authctxt->pw) == 0) 215 return; 216 #endif 217 if (authenticated) 218 authctxt->method->authenticated = 1; 219 } 220 221 /* return 1 if user allows given key */ 222 static int 223 user_key_allowed2(struct passwd *pw, Key *key, char *file) 224 { 225 char line[8192]; 226 int found_key = 0; 227 FILE *f; 228 u_long linenum = 0; 229 struct stat st; 230 Key *found; 231 char *fp; 232 233 if (pw == NULL) 234 return 0; 235 236 /* Temporarily use the user's uid. */ 237 temporarily_use_uid(pw); 238 239 debug("trying public key file %s", file); 240 241 /* Fail quietly if file does not exist */ 242 if (stat(file, &st) < 0) { 243 /* Restore the privileged uid. */ 244 restore_uid(); 245 return 0; 246 } 247 /* Open the file containing the authorized keys. */ 248 f = fopen(file, "r"); 249 if (!f) { 250 /* Restore the privileged uid. */ 251 restore_uid(); 252 return 0; 253 } 254 if (options.strict_modes && 255 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 256 (void) fclose(f); 257 log("Authentication refused: %s", line); 258 restore_uid(); 259 return 0; 260 } 261 262 found_key = 0; 263 found = key_new(key->type); 264 265 while (fgets(line, sizeof(line), f)) { 266 char *cp, *options = NULL; 267 linenum++; 268 /* Skip leading whitespace, empty and comment lines. */ 269 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 270 ; 271 if (!*cp || *cp == '\n' || *cp == '#') 272 continue; 273 274 if (key_read(found, &cp) != 1) { 275 /* no key? check if there are options for this key */ 276 int quoted = 0; 277 debug2("user_key_allowed: check options: '%s'", cp); 278 options = cp; 279 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 280 if (*cp == '\\' && cp[1] == '"') 281 cp++; /* Skip both */ 282 else if (*cp == '"') 283 quoted = !quoted; 284 } 285 /* Skip remaining whitespace. */ 286 for (; *cp == ' ' || *cp == '\t'; cp++) 287 ; 288 if (key_read(found, &cp) != 1) { 289 debug2("user_key_allowed: advance: '%s'", cp); 290 /* still no key? advance to next line*/ 291 continue; 292 } 293 } 294 if (key_equal(found, key) && 295 auth_parse_options(pw, options, file, linenum) == 1) { 296 found_key = 1; 297 debug("matching key found: file %s, line %lu", 298 file, linenum); 299 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 300 verbose("Found matching %s key: %s", 301 key_type(found), fp); 302 xfree(fp); 303 break; 304 } 305 } 306 restore_uid(); 307 (void) fclose(f); 308 key_free(found); 309 if (!found_key) 310 debug2("key not found"); 311 return found_key; 312 } 313 314 /* check whether given key is in .ssh/authorized_keys* */ 315 int 316 user_key_allowed(struct passwd *pw, Key *key) 317 { 318 int success; 319 char *file; 320 321 if (pw == NULL) 322 return 0; 323 324 file = authorized_keys_file(pw); 325 success = user_key_allowed2(pw, key, file); 326 xfree(file); 327 if (success) 328 return success; 329 330 /* try suffix "2" for backward compat, too */ 331 file = authorized_keys_file2(pw); 332 success = user_key_allowed2(pw, key, file); 333 xfree(file); 334 return success; 335 } 336 337 static 338 void 339 userauth_pubkey_abandon(Authctxt *authctxt, Authmethod *method) 340 { 341 if (!authctxt || !method) 342 return; 343 344 if (method->method_data) { 345 method->abandons++; 346 method->attempts++; 347 key_free((Key *) method->method_data); 348 method->method_data = NULL; 349 } 350 } 351 352 Authmethod method_pubkey = { 353 "publickey", 354 &options.pubkey_authentication, 355 userauth_pubkey, 356 userauth_pubkey_abandon, 357 NULL, NULL, /* method data and hist data */ 358 0, /* not initial userauth */ 359 0, 0, 0, /* counters */ 360 0, 0, 0, 0, 0, 0 /* state */ 361 }; 362