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 1.6 2004/01/19 21:25:15 markus Exp $"); 27 28 #include "ssh2.h" 29 #include "xmalloc.h" 30 #include "packet.h" 31 #include "buffer.h" 32 #include "log.h" 33 #include "servconf.h" 34 #include "compat.h" 35 #include "bufaux.h" 36 #include "auth.h" 37 #include "key.h" 38 #include "pathnames.h" 39 #include "uidswap.h" 40 #include "auth-options.h" 41 #include "canohost.h" 42 #include "monitor_wrap.h" 43 44 /* import */ 45 extern ServerOptions options; 46 extern u_char *session_id2; 47 extern u_int session_id2_len; 48 49 static int 50 userauth_pubkey(Authctxt *authctxt) 51 { 52 Buffer b; 53 Key *key = NULL; 54 char *pkalg; 55 u_char *pkblob, *sig; 56 u_int alen, blen, slen; 57 int have_sig, pktype; 58 int authenticated = 0; 59 60 if (!authctxt->valid) { 61 debug2("userauth_pubkey: disabled because of invalid user"); 62 return 0; 63 } 64 have_sig = packet_get_char(); 65 if (datafellows & SSH_BUG_PKAUTH) { 66 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 67 /* no explicit pkalg given */ 68 pkblob = packet_get_string(&blen); 69 buffer_init(&b); 70 buffer_append(&b, pkblob, blen); 71 /* so we have to extract the pkalg from the pkblob */ 72 pkalg = buffer_get_string(&b, &alen); 73 buffer_free(&b); 74 } else { 75 pkalg = packet_get_string(&alen); 76 pkblob = packet_get_string(&blen); 77 } 78 pktype = key_type_from_name(pkalg); 79 if (pktype == KEY_UNSPEC) { 80 /* this is perfectly legal */ 81 logit("userauth_pubkey: unsupported public key algorithm: %s", 82 pkalg); 83 goto done; 84 } 85 key = key_from_blob(pkblob, blen); 86 if (key == NULL) { 87 error("userauth_pubkey: cannot decode key: %s", pkalg); 88 goto done; 89 } 90 if (key->type != pktype) { 91 error("userauth_pubkey: type mismatch for decoded key " 92 "(received %d, expected %d)", key->type, pktype); 93 goto done; 94 } 95 if (have_sig) { 96 sig = packet_get_string(&slen); 97 packet_check_eom(); 98 buffer_init(&b); 99 if (datafellows & SSH_OLD_SESSIONID) { 100 buffer_append(&b, session_id2, session_id2_len); 101 } else { 102 buffer_put_string(&b, session_id2, session_id2_len); 103 } 104 /* reconstruct packet */ 105 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 106 buffer_put_cstring(&b, authctxt->user); 107 buffer_put_cstring(&b, 108 datafellows & SSH_BUG_PKSERVICE ? 109 "ssh-userauth" : 110 authctxt->service); 111 if (datafellows & SSH_BUG_PKAUTH) { 112 buffer_put_char(&b, have_sig); 113 } else { 114 buffer_put_cstring(&b, "publickey"); 115 buffer_put_char(&b, have_sig); 116 buffer_put_cstring(&b, pkalg); 117 } 118 buffer_put_string(&b, pkblob, blen); 119 #ifdef DEBUG_PK 120 buffer_dump(&b); 121 #endif 122 /* test for correct signature */ 123 authenticated = 0; 124 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 125 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 126 buffer_len(&b))) == 1) 127 authenticated = 1; 128 buffer_free(&b); 129 xfree(sig); 130 } else { 131 debug("test whether pkalg/pkblob are acceptable"); 132 packet_check_eom(); 133 134 /* XXX fake reply and always send PK_OK ? */ 135 /* 136 * XXX this allows testing whether a user is allowed 137 * to login: if you happen to have a valid pubkey this 138 * message is sent. the message is NEVER sent at all 139 * if a user is not allowed to login. is this an 140 * issue? -markus 141 */ 142 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 143 packet_start(SSH2_MSG_USERAUTH_PK_OK); 144 packet_put_string(pkalg, alen); 145 packet_put_string(pkblob, blen); 146 packet_send(); 147 packet_write_wait(); 148 authctxt->postponed = 1; 149 } 150 } 151 if (authenticated != 1) 152 auth_clear_options(); 153 done: 154 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 155 if (key != NULL) 156 key_free(key); 157 xfree(pkalg); 158 xfree(pkblob); 159 #ifdef HAVE_CYGWIN 160 if (check_nt_auth(0, authctxt->pw) == 0) 161 return(0); 162 #endif 163 return authenticated; 164 } 165 166 /* return 1 if user allows given key */ 167 static int 168 user_key_allowed2(struct passwd *pw, Key *key, char *file) 169 { 170 char line[8192]; 171 int found_key = 0; 172 FILE *f; 173 u_long linenum = 0; 174 struct stat st; 175 Key *found; 176 char *fp; 177 178 /* Temporarily use the user's uid. */ 179 temporarily_use_uid(pw); 180 181 debug("trying public key file %s", file); 182 183 /* Fail quietly if file does not exist */ 184 if (stat(file, &st) < 0) { 185 /* Restore the privileged uid. */ 186 restore_uid(); 187 return 0; 188 } 189 /* Open the file containing the authorized keys. */ 190 f = fopen(file, "r"); 191 if (!f) { 192 /* Restore the privileged uid. */ 193 restore_uid(); 194 return 0; 195 } 196 if (options.strict_modes && 197 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 198 fclose(f); 199 logit("Authentication refused: %s", line); 200 restore_uid(); 201 return 0; 202 } 203 204 found_key = 0; 205 found = key_new(key->type); 206 207 while (fgets(line, sizeof(line), f)) { 208 char *cp, *options = NULL; 209 linenum++; 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 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 (key_equal(found, key) && 237 auth_parse_options(pw, options, file, linenum) == 1) { 238 found_key = 1; 239 debug("matching key found: file %s, line %lu", 240 file, linenum); 241 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 242 verbose("Found matching %s key: %s", 243 key_type(found), fp); 244 xfree(fp); 245 break; 246 } 247 } 248 restore_uid(); 249 fclose(f); 250 key_free(found); 251 if (!found_key) 252 debug2("key not found"); 253 return found_key; 254 } 255 256 /* check whether given key is in .ssh/authorized_keys* */ 257 int 258 user_key_allowed(struct passwd *pw, Key *key) 259 { 260 int success; 261 char *file; 262 263 file = authorized_keys_file(pw); 264 success = user_key_allowed2(pw, key, file); 265 xfree(file); 266 if (success) 267 return success; 268 269 /* try suffix "2" for backward compat, too */ 270 file = authorized_keys_file2(pw); 271 success = user_key_allowed2(pw, key, file); 272 xfree(file); 273 return success; 274 } 275 276 Authmethod method_pubkey = { 277 "publickey", 278 userauth_pubkey, 279 &options.pubkey_authentication 280 }; 281