1 /* $OpenBSD: ssh-keysign.c,v 1.29 2006/08/03 03:34:42 deraadt Exp $ */ 2 /* 3 * Copyright (c) 2002 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 <fcntl.h> 29 #ifdef HAVE_PATHS_H 30 #include <paths.h> 31 #endif 32 #include <pwd.h> 33 #include <stdarg.h> 34 #include <stdlib.h> 35 #include <string.h> 36 #include <unistd.h> 37 38 #include <openssl/evp.h> 39 #include <openssl/rand.h> 40 #include <openssl/rsa.h> 41 42 #include "xmalloc.h" 43 #include "log.h" 44 #include "key.h" 45 #include "ssh.h" 46 #include "ssh2.h" 47 #include "misc.h" 48 #include "buffer.h" 49 #include "authfile.h" 50 #include "msg.h" 51 #include "canohost.h" 52 #include "pathnames.h" 53 #include "readconf.h" 54 #include "uidswap.h" 55 56 /* XXX readconf.c needs these */ 57 uid_t original_real_uid; 58 59 extern char *__progname; 60 61 static int 62 valid_request(struct passwd *pw, char *host, Key **ret, u_char *data, 63 u_int datalen) 64 { 65 Buffer b; 66 Key *key = NULL; 67 u_char *pkblob; 68 u_int blen, len; 69 char *pkalg, *p; 70 int pktype, fail; 71 72 fail = 0; 73 74 buffer_init(&b); 75 buffer_append(&b, data, datalen); 76 77 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 78 p = buffer_get_string(&b, &len); 79 if (len != 20 && len != 32) 80 fail++; 81 xfree(p); 82 83 if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST) 84 fail++; 85 86 /* server user */ 87 buffer_skip_string(&b); 88 89 /* service */ 90 p = buffer_get_string(&b, NULL); 91 if (strcmp("ssh-connection", p) != 0) 92 fail++; 93 xfree(p); 94 95 /* method */ 96 p = buffer_get_string(&b, NULL); 97 if (strcmp("hostbased", p) != 0) 98 fail++; 99 xfree(p); 100 101 /* pubkey */ 102 pkalg = buffer_get_string(&b, NULL); 103 pkblob = buffer_get_string(&b, &blen); 104 105 pktype = key_type_from_name(pkalg); 106 if (pktype == KEY_UNSPEC) 107 fail++; 108 else if ((key = key_from_blob(pkblob, blen)) == NULL) 109 fail++; 110 else if (key->type != pktype) 111 fail++; 112 xfree(pkalg); 113 xfree(pkblob); 114 115 /* client host name, handle trailing dot */ 116 p = buffer_get_string(&b, &len); 117 debug2("valid_request: check expect chost %s got %s", host, p); 118 if (strlen(host) != len - 1) 119 fail++; 120 else if (p[len - 1] != '.') 121 fail++; 122 else if (strncasecmp(host, p, len - 1) != 0) 123 fail++; 124 xfree(p); 125 126 /* local user */ 127 p = buffer_get_string(&b, NULL); 128 129 if (strcmp(pw->pw_name, p) != 0) 130 fail++; 131 xfree(p); 132 133 /* end of message */ 134 if (buffer_len(&b) != 0) 135 fail++; 136 buffer_free(&b); 137 138 debug3("valid_request: fail %d", fail); 139 140 if (fail && key != NULL) 141 key_free(key); 142 else 143 *ret = key; 144 145 return (fail ? -1 : 0); 146 } 147 148 int 149 main(int argc, char **argv) 150 { 151 Buffer b; 152 Options options; 153 Key *keys[2], *key = NULL; 154 struct passwd *pw; 155 int key_fd[2], i, found, version = 2, fd; 156 u_char *signature, *data; 157 char *host; 158 u_int slen, dlen; 159 u_int32_t rnd[256]; 160 161 /* Ensure that stdin and stdout are connected */ 162 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 163 exit(1); 164 /* Leave /dev/null fd iff it is attached to stderr */ 165 if (fd > 2) 166 close(fd); 167 168 key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 169 key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 170 171 original_real_uid = getuid(); /* XXX readconf.c needs this */ 172 if ((pw = getpwuid(original_real_uid)) == NULL) 173 fatal("getpwuid failed"); 174 pw = pwcopy(pw); 175 176 permanently_set_uid(pw); 177 178 init_rng(); 179 seed_rng(); 180 arc4random_stir(); 181 182 #ifdef DEBUG_SSH_KEYSIGN 183 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 184 #endif 185 186 /* verify that ssh-keysign is enabled by the admin */ 187 initialize_options(&options); 188 (void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0); 189 fill_default_options(&options); 190 if (options.enable_ssh_keysign != 1) 191 fatal("ssh-keysign not enabled in %s", 192 _PATH_HOST_CONFIG_FILE); 193 194 if (key_fd[0] == -1 && key_fd[1] == -1) 195 fatal("could not open any host key"); 196 197 SSLeay_add_all_algorithms(); 198 for (i = 0; i < 256; i++) 199 rnd[i] = arc4random(); 200 RAND_seed(rnd, sizeof(rnd)); 201 202 found = 0; 203 for (i = 0; i < 2; i++) { 204 keys[i] = NULL; 205 if (key_fd[i] == -1) 206 continue; 207 keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC, 208 NULL, NULL); 209 close(key_fd[i]); 210 if (keys[i] != NULL) 211 found = 1; 212 } 213 if (!found) 214 fatal("no hostkey found"); 215 216 buffer_init(&b); 217 if (ssh_msg_recv(STDIN_FILENO, &b) < 0) 218 fatal("ssh_msg_recv failed"); 219 if (buffer_get_char(&b) != version) 220 fatal("bad version"); 221 fd = buffer_get_int(&b); 222 if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO)) 223 fatal("bad fd"); 224 if ((host = get_local_name(fd)) == NULL) 225 fatal("cannot get sockname for fd"); 226 227 data = buffer_get_string(&b, &dlen); 228 if (valid_request(pw, host, &key, data, dlen) < 0) 229 fatal("not a valid request"); 230 xfree(host); 231 232 found = 0; 233 for (i = 0; i < 2; i++) { 234 if (keys[i] != NULL && 235 key_equal(key, keys[i])) { 236 found = 1; 237 break; 238 } 239 } 240 if (!found) 241 fatal("no matching hostkey found"); 242 243 if (key_sign(keys[i], &signature, &slen, data, dlen) != 0) 244 fatal("key_sign failed"); 245 xfree(data); 246 247 /* send reply */ 248 buffer_clear(&b); 249 buffer_put_string(&b, signature, slen); 250 if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1) 251 fatal("ssh_msg_send failed"); 252 253 return (0); 254 } 255