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 #include "includes.h" 26 RCSID("$OpenBSD: auth2-pubkey.c,v 1.9 2004/12/11 01:48:56 dtucker Exp $"); 27 28 #include "ssh.h" 29 #include "ssh2.h" 30 #include "xmalloc.h" 31 #include "packet.h" 32 #include "buffer.h" 33 #include "log.h" 34 #include "servconf.h" 35 #include "compat.h" 36 #include "bufaux.h" 37 #include "auth.h" 38 #include "key.h" 39 #include "pathnames.h" 40 #include "uidswap.h" 41 #include "auth-options.h" 42 #include "canohost.h" 43 #include "monitor_wrap.h" 44 #include "misc.h" 45 46 /* import */ 47 extern ServerOptions options; 48 extern u_char *session_id2; 49 extern u_int session_id2_len; 50 51 static int 52 userauth_pubkey(Authctxt *authctxt) 53 { 54 Buffer b; 55 Key *key = NULL; 56 char *pkalg; 57 u_char *pkblob, *sig; 58 u_int alen, blen, slen; 59 int have_sig, pktype; 60 int authenticated = 0; 61 62 if (!authctxt->valid) { 63 debug2("userauth_pubkey: disabled because of invalid user"); 64 return 0; 65 } 66 have_sig = packet_get_char(); 67 if (datafellows & SSH_BUG_PKAUTH) { 68 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 69 /* no explicit pkalg given */ 70 pkblob = packet_get_string(&blen); 71 buffer_init(&b); 72 buffer_append(&b, pkblob, blen); 73 /* so we have to extract the pkalg from the pkblob */ 74 pkalg = buffer_get_string(&b, &alen); 75 buffer_free(&b); 76 } else { 77 pkalg = packet_get_string(&alen); 78 pkblob = packet_get_string(&blen); 79 } 80 pktype = key_type_from_name(pkalg); 81 if (pktype == KEY_UNSPEC) { 82 /* this is perfectly legal */ 83 logit("userauth_pubkey: unsupported public key algorithm: %s", 84 pkalg); 85 goto done; 86 } 87 key = key_from_blob(pkblob, blen); 88 if (key == NULL) { 89 error("userauth_pubkey: cannot decode key: %s", pkalg); 90 goto done; 91 } 92 if (key->type != pktype) { 93 error("userauth_pubkey: type mismatch for decoded key " 94 "(received %d, expected %d)", key->type, pktype); 95 goto done; 96 } 97 if (have_sig) { 98 sig = packet_get_string(&slen); 99 packet_check_eom(); 100 buffer_init(&b); 101 if (datafellows & SSH_OLD_SESSIONID) { 102 buffer_append(&b, session_id2, session_id2_len); 103 } else { 104 buffer_put_string(&b, session_id2, session_id2_len); 105 } 106 /* reconstruct packet */ 107 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 108 buffer_put_cstring(&b, authctxt->user); 109 buffer_put_cstring(&b, 110 datafellows & SSH_BUG_PKSERVICE ? 111 "ssh-userauth" : 112 authctxt->service); 113 if (datafellows & SSH_BUG_PKAUTH) { 114 buffer_put_char(&b, have_sig); 115 } else { 116 buffer_put_cstring(&b, "publickey"); 117 buffer_put_char(&b, have_sig); 118 buffer_put_cstring(&b, pkalg); 119 } 120 buffer_put_string(&b, pkblob, blen); 121 #ifdef DEBUG_PK 122 buffer_dump(&b); 123 #endif 124 /* test for correct signature */ 125 authenticated = 0; 126 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 127 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 128 buffer_len(&b))) == 1) 129 authenticated = 1; 130 buffer_free(&b); 131 xfree(sig); 132 } else { 133 debug("test whether pkalg/pkblob are acceptable"); 134 packet_check_eom(); 135 136 /* XXX fake reply and always send PK_OK ? */ 137 /* 138 * XXX this allows testing whether a user is allowed 139 * to login: if you happen to have a valid pubkey this 140 * message is sent. the message is NEVER sent at all 141 * if a user is not allowed to login. is this an 142 * issue? -markus 143 */ 144 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 145 packet_start(SSH2_MSG_USERAUTH_PK_OK); 146 packet_put_string(pkalg, alen); 147 packet_put_string(pkblob, blen); 148 packet_send(); 149 packet_write_wait(); 150 authctxt->postponed = 1; 151 } 152 } 153 if (authenticated != 1) 154 auth_clear_options(); 155 done: 156 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 157 if (key != NULL) 158 key_free(key); 159 xfree(pkalg); 160 xfree(pkblob); 161 #ifdef HAVE_CYGWIN 162 if (check_nt_auth(0, authctxt->pw) == 0) 163 authenticated = 0; 164 #endif 165 return authenticated; 166 } 167 168 /* return 1 if user allows given key */ 169 static int 170 user_key_allowed2(struct passwd *pw, Key *key, char *file) 171 { 172 char line[SSH_MAX_PUBKEY_BYTES]; 173 int found_key = 0; 174 FILE *f; 175 u_long linenum = 0; 176 struct stat st; 177 Key *found; 178 char *fp; 179 180 /* Temporarily use the user's uid. */ 181 temporarily_use_uid(pw); 182 183 debug("trying public key file %s", file); 184 185 /* Fail quietly if file does not exist */ 186 if (stat(file, &st) < 0) { 187 /* Restore the privileged uid. */ 188 restore_uid(); 189 return 0; 190 } 191 /* Open the file containing the authorized keys. */ 192 f = fopen(file, "r"); 193 if (!f) { 194 /* Restore the privileged uid. */ 195 restore_uid(); 196 return 0; 197 } 198 if (options.strict_modes && 199 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 200 fclose(f); 201 logit("Authentication refused: %s", line); 202 restore_uid(); 203 return 0; 204 } 205 206 found_key = 0; 207 found = key_new(key->type); 208 209 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 210 char *cp, *key_options = NULL; 211 212 /* Skip leading whitespace, empty and comment lines. */ 213 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 214 ; 215 if (!*cp || *cp == '\n' || *cp == '#') 216 continue; 217 218 if (key_read(found, &cp) != 1) { 219 /* no key? check if there are options for this key */ 220 int quoted = 0; 221 debug2("user_key_allowed: check options: '%s'", cp); 222 key_options = cp; 223 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 224 if (*cp == '\\' && cp[1] == '"') 225 cp++; /* Skip both */ 226 else if (*cp == '"') 227 quoted = !quoted; 228 } 229 /* Skip remaining whitespace. */ 230 for (; *cp == ' ' || *cp == '\t'; cp++) 231 ; 232 if (key_read(found, &cp) != 1) { 233 debug2("user_key_allowed: advance: '%s'", cp); 234 /* still no key? advance to next line*/ 235 continue; 236 } 237 } 238 if (key_equal(found, key) && 239 auth_parse_options(pw, key_options, file, linenum) == 1) { 240 found_key = 1; 241 debug("matching key found: file %s, line %lu", 242 file, linenum); 243 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 244 verbose("Found matching %s key: %s", 245 key_type(found), fp); 246 xfree(fp); 247 break; 248 } 249 } 250 restore_uid(); 251 fclose(f); 252 key_free(found); 253 if (!found_key) 254 debug2("key not found"); 255 return found_key; 256 } 257 258 /* check whether given key is in .ssh/authorized_keys* */ 259 int 260 user_key_allowed(struct passwd *pw, Key *key) 261 { 262 int success; 263 char *file; 264 265 file = authorized_keys_file(pw); 266 success = user_key_allowed2(pw, key, file); 267 xfree(file); 268 if (success) 269 return success; 270 271 /* try suffix "2" for backward compat, too */ 272 file = authorized_keys_file2(pw); 273 success = user_key_allowed2(pw, key, file); 274 xfree(file); 275 return success; 276 } 277 278 Authmethod method_pubkey = { 279 "publickey", 280 userauth_pubkey, 281 &options.pubkey_authentication 282 }; 283