1 /* $OpenBSD: ssh-keysign.c,v 1.55 2018/07/27 05:34:42 dtucker 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 static int 66 valid_request(struct passwd *pw, char *host, struct sshkey **ret, 67 u_char *data, size_t datalen) 68 { 69 struct sshbuf *b; 70 struct sshkey *key = NULL; 71 u_char type, *pkblob; 72 char *p; 73 size_t blen, len; 74 char *pkalg, *luser; 75 int r, pktype, fail; 76 77 if (ret != NULL) 78 *ret = NULL; 79 fail = 0; 80 81 if ((b = sshbuf_from(data, datalen)) == NULL) 82 fatal("%s: sshbuf_from failed", __func__); 83 84 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 85 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 86 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 87 if (len != 20 && len != 32) 88 fail++; 89 90 if ((r = sshbuf_get_u8(b, &type)) != 0) 91 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 92 if (type != SSH2_MSG_USERAUTH_REQUEST) 93 fail++; 94 95 /* server user */ 96 if ((r = sshbuf_skip_string(b)) != 0) 97 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 98 99 /* service */ 100 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 101 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 102 if (strcmp("ssh-connection", p) != 0) 103 fail++; 104 free(p); 105 106 /* method */ 107 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 108 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 109 if (strcmp("hostbased", p) != 0) 110 fail++; 111 free(p); 112 113 /* pubkey */ 114 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 115 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 116 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 117 118 pktype = sshkey_type_from_name(pkalg); 119 if (pktype == KEY_UNSPEC) 120 fail++; 121 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 122 error("%s: bad key blob: %s", __func__, ssh_err(r)); 123 fail++; 124 } else if (key->type != pktype) 125 fail++; 126 free(pkalg); 127 free(pkblob); 128 129 /* client host name, handle trailing dot */ 130 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 131 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 132 debug2("%s: check expect chost %s got %s", __func__, host, p); 133 if (strlen(host) != len - 1) 134 fail++; 135 else if (p[len - 1] != '.') 136 fail++; 137 else if (strncasecmp(host, p, len - 1) != 0) 138 fail++; 139 free(p); 140 141 /* local user */ 142 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 143 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 144 145 if (strcmp(pw->pw_name, luser) != 0) 146 fail++; 147 free(luser); 148 149 /* end of message */ 150 if (sshbuf_len(b) != 0) 151 fail++; 152 sshbuf_free(b); 153 154 debug3("%s: fail %d", __func__, fail); 155 156 if (fail) 157 sshkey_free(key); 158 else if (ret != NULL) 159 *ret = key; 160 161 return (fail ? -1 : 0); 162 } 163 164 int 165 main(int argc, char **argv) 166 { 167 struct sshbuf *b; 168 Options options; 169 #define NUM_KEYTYPES 5 170 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 171 struct passwd *pw; 172 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 173 u_char *signature, *data, rver; 174 char *host, *fp; 175 size_t slen, dlen; 176 #ifdef WITH_OPENSSL 177 u_int32_t rnd[256]; 178 #endif 179 180 ssh_malloc_init(); /* must be called before any mallocs */ 181 if (pledge("stdio rpath getpw dns id", NULL) != 0) 182 fatal("%s: pledge: %s", __progname, strerror(errno)); 183 184 /* Ensure that stdin and stdout are connected */ 185 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 186 exit(1); 187 /* Leave /dev/null fd iff it is attached to stderr */ 188 if (fd > 2) 189 close(fd); 190 191 i = 0; 192 /* XXX This really needs to read sshd_config for the paths */ 193 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 194 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 195 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 196 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 197 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 198 199 if ((pw = getpwuid(getuid())) == NULL) 200 fatal("getpwuid failed"); 201 pw = pwcopy(pw); 202 203 permanently_set_uid(pw); 204 205 seed_rng(); 206 207 #ifdef DEBUG_SSH_KEYSIGN 208 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 209 #endif 210 211 /* verify that ssh-keysign is enabled by the admin */ 212 initialize_options(&options); 213 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0); 214 fill_default_options(&options); 215 if (options.enable_ssh_keysign != 1) 216 fatal("ssh-keysign not enabled in %s", 217 _PATH_HOST_CONFIG_FILE); 218 219 for (i = found = 0; i < NUM_KEYTYPES; i++) { 220 if (key_fd[i] != -1) 221 found = 1; 222 } 223 if (found == 0) 224 fatal("could not open any host key"); 225 226 #ifdef WITH_OPENSSL 227 OpenSSL_add_all_algorithms(); 228 arc4random_buf(rnd, sizeof(rnd)); 229 RAND_seed(rnd, sizeof(rnd)); 230 #endif 231 232 found = 0; 233 for (i = 0; i < NUM_KEYTYPES; i++) { 234 keys[i] = NULL; 235 if (key_fd[i] == -1) 236 continue; 237 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 238 NULL, &key, NULL); 239 close(key_fd[i]); 240 if (r != 0) 241 debug("parse key %d: %s", i, ssh_err(r)); 242 else if (key != NULL) { 243 keys[i] = key; 244 found = 1; 245 } 246 } 247 if (!found) 248 fatal("no hostkey found"); 249 250 if (pledge("stdio dns", NULL) != 0) 251 fatal("%s: pledge: %s", __progname, strerror(errno)); 252 253 if ((b = sshbuf_new()) == NULL) 254 fatal("%s: sshbuf_new failed", __progname); 255 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 256 fatal("ssh_msg_recv failed"); 257 if ((r = sshbuf_get_u8(b, &rver)) != 0) 258 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 259 if (rver != version) 260 fatal("bad version: received %d, expected %d", rver, version); 261 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 262 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 263 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 264 fatal("bad fd"); 265 if ((host = get_local_name(fd)) == NULL) 266 fatal("cannot get local name for fd"); 267 268 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 269 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 270 if (valid_request(pw, host, &key, data, dlen) < 0) 271 fatal("not a valid request"); 272 free(host); 273 274 found = 0; 275 for (i = 0; i < NUM_KEYTYPES; i++) { 276 if (keys[i] != NULL && 277 sshkey_equal_public(key, keys[i])) { 278 found = 1; 279 break; 280 } 281 } 282 if (!found) { 283 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 284 SSH_FP_DEFAULT)) == NULL) 285 fatal("%s: sshkey_fingerprint failed", __progname); 286 fatal("no matching hostkey found for key %s %s", 287 sshkey_type(key), fp ? fp : ""); 288 } 289 290 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0)) 291 != 0) 292 fatal("sshkey_sign failed: %s", ssh_err(r)); 293 free(data); 294 295 /* send reply */ 296 sshbuf_reset(b); 297 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 298 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 299 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 300 fatal("ssh_msg_send failed"); 301 302 return (0); 303 } 304