1 /* $OpenBSD: auth2-pubkey.c,v 1.15 2006/08/03 03:34:41 deraadt 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 <pwd.h> 32 #include <stdio.h> 33 #include <stdarg.h> 34 35 #include "xmalloc.h" 36 #include "ssh.h" 37 #include "ssh2.h" 38 #include "packet.h" 39 #include "buffer.h" 40 #include "log.h" 41 #include "servconf.h" 42 #include "compat.h" 43 #include "key.h" 44 #include "hostfile.h" 45 #include "auth.h" 46 #include "pathnames.h" 47 #include "uidswap.h" 48 #include "auth-options.h" 49 #include "canohost.h" 50 #ifdef GSSAPI 51 #include "ssh-gss.h" 52 #endif 53 #include "monitor_wrap.h" 54 #include "misc.h" 55 56 /* import */ 57 extern ServerOptions options; 58 extern u_char *session_id2; 59 extern u_int session_id2_len; 60 61 static int 62 userauth_pubkey(Authctxt *authctxt) 63 { 64 Buffer b; 65 Key *key = NULL; 66 char *pkalg; 67 u_char *pkblob, *sig; 68 u_int alen, blen, slen; 69 int have_sig, pktype; 70 int authenticated = 0; 71 72 if (!authctxt->valid) { 73 debug2("userauth_pubkey: disabled because of invalid user"); 74 return 0; 75 } 76 have_sig = packet_get_char(); 77 if (datafellows & SSH_BUG_PKAUTH) { 78 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 79 /* no explicit pkalg given */ 80 pkblob = packet_get_string(&blen); 81 buffer_init(&b); 82 buffer_append(&b, pkblob, blen); 83 /* so we have to extract the pkalg from the pkblob */ 84 pkalg = buffer_get_string(&b, &alen); 85 buffer_free(&b); 86 } else { 87 pkalg = packet_get_string(&alen); 88 pkblob = packet_get_string(&blen); 89 } 90 pktype = key_type_from_name(pkalg); 91 if (pktype == KEY_UNSPEC) { 92 /* this is perfectly legal */ 93 logit("userauth_pubkey: unsupported public key algorithm: %s", 94 pkalg); 95 goto done; 96 } 97 key = key_from_blob(pkblob, blen); 98 if (key == NULL) { 99 error("userauth_pubkey: cannot decode key: %s", pkalg); 100 goto done; 101 } 102 if (key->type != pktype) { 103 error("userauth_pubkey: type mismatch for decoded key " 104 "(received %d, expected %d)", key->type, pktype); 105 goto done; 106 } 107 if (have_sig) { 108 sig = packet_get_string(&slen); 109 packet_check_eom(); 110 buffer_init(&b); 111 if (datafellows & SSH_OLD_SESSIONID) { 112 buffer_append(&b, session_id2, session_id2_len); 113 } else { 114 buffer_put_string(&b, session_id2, session_id2_len); 115 } 116 /* reconstruct packet */ 117 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 118 buffer_put_cstring(&b, authctxt->user); 119 buffer_put_cstring(&b, 120 datafellows & SSH_BUG_PKSERVICE ? 121 "ssh-userauth" : 122 authctxt->service); 123 if (datafellows & SSH_BUG_PKAUTH) { 124 buffer_put_char(&b, have_sig); 125 } else { 126 buffer_put_cstring(&b, "publickey"); 127 buffer_put_char(&b, have_sig); 128 buffer_put_cstring(&b, pkalg); 129 } 130 buffer_put_string(&b, pkblob, blen); 131 #ifdef DEBUG_PK 132 buffer_dump(&b); 133 #endif 134 /* test for correct signature */ 135 authenticated = 0; 136 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 137 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 138 buffer_len(&b))) == 1) 139 authenticated = 1; 140 buffer_free(&b); 141 xfree(sig); 142 } else { 143 debug("test whether pkalg/pkblob are acceptable"); 144 packet_check_eom(); 145 146 /* XXX fake reply and always send PK_OK ? */ 147 /* 148 * XXX this allows testing whether a user is allowed 149 * to login: if you happen to have a valid pubkey this 150 * message is sent. the message is NEVER sent at all 151 * if a user is not allowed to login. is this an 152 * issue? -markus 153 */ 154 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 155 packet_start(SSH2_MSG_USERAUTH_PK_OK); 156 packet_put_string(pkalg, alen); 157 packet_put_string(pkblob, blen); 158 packet_send(); 159 packet_write_wait(); 160 authctxt->postponed = 1; 161 } 162 } 163 if (authenticated != 1) 164 auth_clear_options(); 165 done: 166 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 167 if (key != NULL) 168 key_free(key); 169 xfree(pkalg); 170 xfree(pkblob); 171 #ifdef HAVE_CYGWIN 172 if (check_nt_auth(0, authctxt->pw) == 0) 173 authenticated = 0; 174 #endif 175 return authenticated; 176 } 177 178 /* return 1 if user allows given key */ 179 static int 180 user_key_allowed2(struct passwd *pw, Key *key, char *file) 181 { 182 char line[SSH_MAX_PUBKEY_BYTES]; 183 int found_key = 0; 184 FILE *f; 185 u_long linenum = 0; 186 struct stat st; 187 Key *found; 188 char *fp; 189 190 /* Temporarily use the user's uid. */ 191 temporarily_use_uid(pw); 192 193 debug("trying public key file %s", file); 194 195 /* Fail quietly if file does not exist */ 196 if (stat(file, &st) < 0) { 197 /* Restore the privileged uid. */ 198 restore_uid(); 199 return 0; 200 } 201 /* Open the file containing the authorized keys. */ 202 f = fopen(file, "r"); 203 if (!f) { 204 /* Restore the privileged uid. */ 205 restore_uid(); 206 return 0; 207 } 208 if (options.strict_modes && 209 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 210 fclose(f); 211 logit("Authentication refused: %s", line); 212 restore_uid(); 213 return 0; 214 } 215 216 found_key = 0; 217 found = key_new(key->type); 218 219 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 220 char *cp, *key_options = NULL; 221 222 /* Skip leading whitespace, empty and comment lines. */ 223 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 224 ; 225 if (!*cp || *cp == '\n' || *cp == '#') 226 continue; 227 228 if (key_read(found, &cp) != 1) { 229 /* no key? check if there are options for this key */ 230 int quoted = 0; 231 debug2("user_key_allowed: check options: '%s'", cp); 232 key_options = cp; 233 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 234 if (*cp == '\\' && cp[1] == '"') 235 cp++; /* Skip both */ 236 else if (*cp == '"') 237 quoted = !quoted; 238 } 239 /* Skip remaining whitespace. */ 240 for (; *cp == ' ' || *cp == '\t'; cp++) 241 ; 242 if (key_read(found, &cp) != 1) { 243 debug2("user_key_allowed: advance: '%s'", cp); 244 /* still no key? advance to next line*/ 245 continue; 246 } 247 } 248 if (key_equal(found, key) && 249 auth_parse_options(pw, key_options, file, linenum) == 1) { 250 found_key = 1; 251 debug("matching key found: file %s, line %lu", 252 file, linenum); 253 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 254 verbose("Found matching %s key: %s", 255 key_type(found), fp); 256 xfree(fp); 257 break; 258 } 259 } 260 restore_uid(); 261 fclose(f); 262 key_free(found); 263 if (!found_key) 264 debug2("key not found"); 265 return found_key; 266 } 267 268 /* check whether given key is in .ssh/authorized_keys* */ 269 int 270 user_key_allowed(struct passwd *pw, Key *key) 271 { 272 int success; 273 char *file; 274 275 file = authorized_keys_file(pw); 276 success = user_key_allowed2(pw, key, file); 277 xfree(file); 278 if (success) 279 return success; 280 281 /* try suffix "2" for backward compat, too */ 282 file = authorized_keys_file2(pw); 283 success = user_key_allowed2(pw, key, file); 284 xfree(file); 285 return success; 286 } 287 288 Authmethod method_pubkey = { 289 "publickey", 290 userauth_pubkey, 291 &options.pubkey_authentication 292 }; 293