1 /* $OpenBSD: ssh-keysign.c,v 1.54 2018/02/23 15:58:38 markus 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 #include <errno.h> 38 39 #ifdef WITH_OPENSSL 40 #include <openssl/evp.h> 41 #include <openssl/rand.h> 42 #include <openssl/rsa.h> 43 #endif 44 45 #include "xmalloc.h" 46 #include "log.h" 47 #include "sshkey.h" 48 #include "ssh.h" 49 #include "ssh2.h" 50 #include "misc.h" 51 #include "sshbuf.h" 52 #include "authfile.h" 53 #include "msg.h" 54 #include "canohost.h" 55 #include "pathnames.h" 56 #include "readconf.h" 57 #include "uidswap.h" 58 #include "sshkey.h" 59 #include "ssherr.h" 60 61 struct ssh *active_state = NULL; /* XXX needed for linking */ 62 63 extern char *__progname; 64 65 /* XXX readconf.c needs these */ 66 uid_t original_real_uid; 67 68 extern char *__progname; 69 70 static int 71 valid_request(struct passwd *pw, char *host, struct sshkey **ret, 72 u_char *data, size_t datalen) 73 { 74 struct sshbuf *b; 75 struct sshkey *key = NULL; 76 u_char type, *pkblob; 77 char *p; 78 size_t blen, len; 79 char *pkalg, *luser; 80 int r, pktype, fail; 81 82 if (ret != NULL) 83 *ret = NULL; 84 fail = 0; 85 86 if ((b = sshbuf_from(data, datalen)) == NULL) 87 fatal("%s: sshbuf_from failed", __func__); 88 89 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 90 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 91 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 92 if (len != 20 && len != 32) 93 fail++; 94 95 if ((r = sshbuf_get_u8(b, &type)) != 0) 96 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 97 if (type != SSH2_MSG_USERAUTH_REQUEST) 98 fail++; 99 100 /* server user */ 101 if ((r = sshbuf_skip_string(b)) != 0) 102 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 103 104 /* service */ 105 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 106 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 107 if (strcmp("ssh-connection", p) != 0) 108 fail++; 109 free(p); 110 111 /* method */ 112 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 113 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 114 if (strcmp("hostbased", p) != 0) 115 fail++; 116 free(p); 117 118 /* pubkey */ 119 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 120 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 121 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 122 123 pktype = sshkey_type_from_name(pkalg); 124 if (pktype == KEY_UNSPEC) 125 fail++; 126 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 127 error("%s: bad key blob: %s", __func__, ssh_err(r)); 128 fail++; 129 } else if (key->type != pktype) 130 fail++; 131 free(pkalg); 132 free(pkblob); 133 134 /* client host name, handle trailing dot */ 135 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 136 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 137 debug2("%s: check expect chost %s got %s", __func__, host, p); 138 if (strlen(host) != len - 1) 139 fail++; 140 else if (p[len - 1] != '.') 141 fail++; 142 else if (strncasecmp(host, p, len - 1) != 0) 143 fail++; 144 free(p); 145 146 /* local user */ 147 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 148 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 149 150 if (strcmp(pw->pw_name, luser) != 0) 151 fail++; 152 free(luser); 153 154 /* end of message */ 155 if (sshbuf_len(b) != 0) 156 fail++; 157 sshbuf_free(b); 158 159 debug3("%s: fail %d", __func__, fail); 160 161 if (fail) 162 sshkey_free(key); 163 else if (ret != NULL) 164 *ret = key; 165 166 return (fail ? -1 : 0); 167 } 168 169 int 170 main(int argc, char **argv) 171 { 172 struct sshbuf *b; 173 Options options; 174 #define NUM_KEYTYPES 5 175 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 176 struct passwd *pw; 177 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 178 u_char *signature, *data, rver; 179 char *host, *fp; 180 size_t slen, dlen; 181 #ifdef WITH_OPENSSL 182 u_int32_t rnd[256]; 183 #endif 184 185 ssh_malloc_init(); /* must be called before any mallocs */ 186 if (pledge("stdio rpath getpw dns id", NULL) != 0) 187 fatal("%s: pledge: %s", __progname, strerror(errno)); 188 189 /* Ensure that stdin and stdout are connected */ 190 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 191 exit(1); 192 /* Leave /dev/null fd iff it is attached to stderr */ 193 if (fd > 2) 194 close(fd); 195 196 i = 0; 197 /* XXX This really needs to read sshd_config for the paths */ 198 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 199 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 200 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 201 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 202 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 203 204 original_real_uid = getuid(); /* XXX readconf.c needs this */ 205 if ((pw = getpwuid(original_real_uid)) == NULL) 206 fatal("getpwuid failed"); 207 pw = pwcopy(pw); 208 209 permanently_set_uid(pw); 210 211 seed_rng(); 212 213 #ifdef DEBUG_SSH_KEYSIGN 214 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 215 #endif 216 217 /* verify that ssh-keysign is enabled by the admin */ 218 initialize_options(&options); 219 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0); 220 fill_default_options(&options); 221 if (options.enable_ssh_keysign != 1) 222 fatal("ssh-keysign not enabled in %s", 223 _PATH_HOST_CONFIG_FILE); 224 225 for (i = found = 0; i < NUM_KEYTYPES; i++) { 226 if (key_fd[i] != -1) 227 found = 1; 228 } 229 if (found == 0) 230 fatal("could not open any host key"); 231 232 #ifdef WITH_OPENSSL 233 OpenSSL_add_all_algorithms(); 234 arc4random_buf(rnd, sizeof(rnd)); 235 RAND_seed(rnd, sizeof(rnd)); 236 #endif 237 238 found = 0; 239 for (i = 0; i < NUM_KEYTYPES; i++) { 240 keys[i] = NULL; 241 if (key_fd[i] == -1) 242 continue; 243 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 244 NULL, &key, NULL); 245 close(key_fd[i]); 246 if (r != 0) 247 debug("parse key %d: %s", i, ssh_err(r)); 248 else if (key != NULL) { 249 keys[i] = key; 250 found = 1; 251 } 252 } 253 if (!found) 254 fatal("no hostkey found"); 255 256 if (pledge("stdio dns", NULL) != 0) 257 fatal("%s: pledge: %s", __progname, strerror(errno)); 258 259 if ((b = sshbuf_new()) == NULL) 260 fatal("%s: sshbuf_new failed", __progname); 261 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 262 fatal("ssh_msg_recv failed"); 263 if ((r = sshbuf_get_u8(b, &rver)) != 0) 264 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 265 if (rver != version) 266 fatal("bad version: received %d, expected %d", rver, version); 267 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 268 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 269 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 270 fatal("bad fd"); 271 if ((host = get_local_name(fd)) == NULL) 272 fatal("cannot get local name for fd"); 273 274 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 275 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 276 if (valid_request(pw, host, &key, data, dlen) < 0) 277 fatal("not a valid request"); 278 free(host); 279 280 found = 0; 281 for (i = 0; i < NUM_KEYTYPES; i++) { 282 if (keys[i] != NULL && 283 sshkey_equal_public(key, keys[i])) { 284 found = 1; 285 break; 286 } 287 } 288 if (!found) { 289 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 290 SSH_FP_DEFAULT)) == NULL) 291 fatal("%s: sshkey_fingerprint failed", __progname); 292 fatal("no matching hostkey found for key %s %s", 293 sshkey_type(key), fp ? fp : ""); 294 } 295 296 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0)) 297 != 0) 298 fatal("sshkey_sign failed: %s", ssh_err(r)); 299 free(data); 300 301 /* send reply */ 302 sshbuf_reset(b); 303 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 304 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 305 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 306 fatal("ssh_msg_send failed"); 307 308 return (0); 309 } 310