1 /* $OpenBSD: auth2-pubkey.c,v 1.19 2008/07/03 21:46:58 otto 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 <unistd.h> 36 37 #include "xmalloc.h" 38 #include "ssh.h" 39 #include "ssh2.h" 40 #include "packet.h" 41 #include "buffer.h" 42 #include "log.h" 43 #include "servconf.h" 44 #include "compat.h" 45 #include "key.h" 46 #include "hostfile.h" 47 #include "authfile.h" 48 #include "auth.h" 49 #include "pathnames.h" 50 #include "uidswap.h" 51 #include "auth-options.h" 52 #include "canohost.h" 53 #ifdef GSSAPI 54 #include "ssh-gss.h" 55 #endif 56 #include "monitor_wrap.h" 57 #include "misc.h" 58 59 /* import */ 60 extern ServerOptions options; 61 extern u_char *session_id2; 62 extern u_int session_id2_len; 63 64 static int 65 userauth_pubkey(Authctxt *authctxt) 66 { 67 Buffer b; 68 Key *key = NULL; 69 char *pkalg; 70 u_char *pkblob, *sig; 71 u_int alen, blen, slen; 72 int have_sig, pktype; 73 int authenticated = 0; 74 75 if (!authctxt->valid) { 76 debug2("userauth_pubkey: disabled because of invalid user"); 77 return 0; 78 } 79 have_sig = packet_get_char(); 80 if (datafellows & SSH_BUG_PKAUTH) { 81 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 82 /* no explicit pkalg given */ 83 pkblob = packet_get_string(&blen); 84 buffer_init(&b); 85 buffer_append(&b, pkblob, blen); 86 /* so we have to extract the pkalg from the pkblob */ 87 pkalg = buffer_get_string(&b, &alen); 88 buffer_free(&b); 89 } else { 90 pkalg = packet_get_string(&alen); 91 pkblob = packet_get_string(&blen); 92 } 93 pktype = key_type_from_name(pkalg); 94 if (pktype == KEY_UNSPEC) { 95 /* this is perfectly legal */ 96 logit("userauth_pubkey: unsupported public key algorithm: %s", 97 pkalg); 98 goto done; 99 } 100 key = key_from_blob(pkblob, blen); 101 if (key == NULL) { 102 error("userauth_pubkey: cannot decode key: %s", pkalg); 103 goto done; 104 } 105 if (key->type != pktype) { 106 error("userauth_pubkey: type mismatch for decoded key " 107 "(received %d, expected %d)", key->type, pktype); 108 goto done; 109 } 110 if (have_sig) { 111 sig = packet_get_string(&slen); 112 packet_check_eom(); 113 buffer_init(&b); 114 if (datafellows & SSH_OLD_SESSIONID) { 115 buffer_append(&b, session_id2, session_id2_len); 116 } else { 117 buffer_put_string(&b, session_id2, session_id2_len); 118 } 119 /* reconstruct packet */ 120 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 121 buffer_put_cstring(&b, authctxt->user); 122 buffer_put_cstring(&b, 123 datafellows & SSH_BUG_PKSERVICE ? 124 "ssh-userauth" : 125 authctxt->service); 126 if (datafellows & SSH_BUG_PKAUTH) { 127 buffer_put_char(&b, have_sig); 128 } else { 129 buffer_put_cstring(&b, "publickey"); 130 buffer_put_char(&b, have_sig); 131 buffer_put_cstring(&b, pkalg); 132 } 133 buffer_put_string(&b, pkblob, blen); 134 #ifdef DEBUG_PK 135 buffer_dump(&b); 136 #endif 137 /* test for correct signature */ 138 authenticated = 0; 139 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 140 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 141 buffer_len(&b))) == 1) 142 authenticated = 1; 143 buffer_free(&b); 144 xfree(sig); 145 } else { 146 debug("test whether pkalg/pkblob are acceptable"); 147 packet_check_eom(); 148 149 /* XXX fake reply and always send PK_OK ? */ 150 /* 151 * XXX this allows testing whether a user is allowed 152 * to login: if you happen to have a valid pubkey this 153 * message is sent. the message is NEVER sent at all 154 * if a user is not allowed to login. is this an 155 * issue? -markus 156 */ 157 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 158 packet_start(SSH2_MSG_USERAUTH_PK_OK); 159 packet_put_string(pkalg, alen); 160 packet_put_string(pkblob, blen); 161 packet_send(); 162 packet_write_wait(); 163 authctxt->postponed = 1; 164 } 165 } 166 if (authenticated != 1) 167 auth_clear_options(); 168 done: 169 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 170 if (key != NULL) 171 key_free(key); 172 xfree(pkalg); 173 xfree(pkblob); 174 #ifdef HAVE_CYGWIN 175 if (check_nt_auth(0, authctxt->pw) == 0) 176 authenticated = 0; 177 #endif 178 return authenticated; 179 } 180 181 /* return 1 if user allows given key */ 182 static int 183 user_key_allowed2(struct passwd *pw, Key *key, char *file) 184 { 185 char line[SSH_MAX_PUBKEY_BYTES]; 186 int found_key = 0; 187 FILE *f; 188 u_long linenum = 0; 189 Key *found; 190 char *fp; 191 192 /* Temporarily use the user's uid. */ 193 temporarily_use_uid(pw); 194 195 debug("trying public key file %s", file); 196 f = auth_openkeyfile(file, pw, options.strict_modes); 197 198 if (!f) { 199 restore_uid(); 200 return 0; 201 } 202 203 found_key = 0; 204 found = key_new(key->type); 205 206 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 207 char *cp, *key_options = NULL; 208 209 /* Skip leading whitespace, empty and comment lines. */ 210 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 211 ; 212 if (!*cp || *cp == '\n' || *cp == '#') 213 continue; 214 215 if (key_read(found, &cp) != 1) { 216 /* no key? check if there are options for this key */ 217 int quoted = 0; 218 debug2("user_key_allowed: check options: '%s'", cp); 219 key_options = cp; 220 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 221 if (*cp == '\\' && cp[1] == '"') 222 cp++; /* Skip both */ 223 else if (*cp == '"') 224 quoted = !quoted; 225 } 226 /* Skip remaining whitespace. */ 227 for (; *cp == ' ' || *cp == '\t'; cp++) 228 ; 229 if (key_read(found, &cp) != 1) { 230 debug2("user_key_allowed: advance: '%s'", cp); 231 /* still no key? advance to next line*/ 232 continue; 233 } 234 } 235 if (key_equal(found, key) && 236 auth_parse_options(pw, key_options, file, linenum) == 1) { 237 found_key = 1; 238 debug("matching key found: file %s, line %lu", 239 file, linenum); 240 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 241 verbose("Found matching %s key: %s", 242 key_type(found), fp); 243 xfree(fp); 244 break; 245 } 246 } 247 restore_uid(); 248 fclose(f); 249 key_free(found); 250 if (!found_key) 251 debug2("key not found"); 252 return found_key; 253 } 254 255 /* check whether given key is in .ssh/authorized_keys* */ 256 int 257 user_key_allowed(struct passwd *pw, Key *key) 258 { 259 char *fp; 260 int success; 261 char *file; 262 263 if (blacklisted_key(key)) { 264 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 265 if (options.permit_blacklisted_keys) 266 logit("Public key %s blacklisted (see " 267 "ssh-vulnkey(1)); continuing anyway", fp); 268 else 269 logit("Public key %s blacklisted (see " 270 "ssh-vulnkey(1))", fp); 271 xfree(fp); 272 if (!options.permit_blacklisted_keys) 273 return 0; 274 } 275 276 file = authorized_keys_file(pw); 277 success = user_key_allowed2(pw, key, file); 278 xfree(file); 279 if (success) 280 return success; 281 282 /* try suffix "2" for backward compat, too */ 283 file = authorized_keys_file2(pw); 284 success = user_key_allowed2(pw, key, file); 285 xfree(file); 286 return success; 287 } 288 289 Authmethod method_pubkey = { 290 "publickey", 291 userauth_pubkey, 292 &options.pubkey_authentication 293 }; 294