1 /* $OpenBSD: ssh-keysign.c,v 1.56 2018/11/23 05:08:07 djm 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 #include "openbsd-compat/openssl-compat.h" 44 #endif 45 46 #include "xmalloc.h" 47 #include "log.h" 48 #include "sshkey.h" 49 #include "ssh.h" 50 #include "ssh2.h" 51 #include "misc.h" 52 #include "sshbuf.h" 53 #include "authfile.h" 54 #include "msg.h" 55 #include "canohost.h" 56 #include "pathnames.h" 57 #include "readconf.h" 58 #include "uidswap.h" 59 #include "sshkey.h" 60 #include "ssherr.h" 61 62 extern char *__progname; 63 64 static int 65 valid_request(struct passwd *pw, char *host, struct sshkey **ret, 66 u_char *data, size_t datalen) 67 { 68 struct sshbuf *b; 69 struct sshkey *key = NULL; 70 u_char type, *pkblob; 71 char *p; 72 size_t blen, len; 73 char *pkalg, *luser; 74 int r, pktype, fail; 75 76 if (ret != NULL) 77 *ret = NULL; 78 fail = 0; 79 80 if ((b = sshbuf_from(data, datalen)) == NULL) 81 fatal("%s: sshbuf_from failed", __func__); 82 83 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 84 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 85 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 86 if (len != 20 && len != 32) 87 fail++; 88 89 if ((r = sshbuf_get_u8(b, &type)) != 0) 90 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 91 if (type != SSH2_MSG_USERAUTH_REQUEST) 92 fail++; 93 94 /* server user */ 95 if ((r = sshbuf_skip_string(b)) != 0) 96 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 97 98 /* service */ 99 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 100 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 101 if (strcmp("ssh-connection", p) != 0) 102 fail++; 103 free(p); 104 105 /* method */ 106 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 107 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 108 if (strcmp("hostbased", p) != 0) 109 fail++; 110 free(p); 111 112 /* pubkey */ 113 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 114 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 115 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 116 117 pktype = sshkey_type_from_name(pkalg); 118 if (pktype == KEY_UNSPEC) 119 fail++; 120 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 121 error("%s: bad key blob: %s", __func__, ssh_err(r)); 122 fail++; 123 } else if (key->type != pktype) 124 fail++; 125 free(pkalg); 126 free(pkblob); 127 128 /* client host name, handle trailing dot */ 129 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 130 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 131 debug2("%s: check expect chost %s got %s", __func__, host, p); 132 if (strlen(host) != len - 1) 133 fail++; 134 else if (p[len - 1] != '.') 135 fail++; 136 else if (strncasecmp(host, p, len - 1) != 0) 137 fail++; 138 free(p); 139 140 /* local user */ 141 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 142 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 143 144 if (strcmp(pw->pw_name, luser) != 0) 145 fail++; 146 free(luser); 147 148 /* end of message */ 149 if (sshbuf_len(b) != 0) 150 fail++; 151 sshbuf_free(b); 152 153 debug3("%s: fail %d", __func__, fail); 154 155 if (fail) 156 sshkey_free(key); 157 else if (ret != NULL) 158 *ret = key; 159 160 return (fail ? -1 : 0); 161 } 162 163 int 164 main(int argc, char **argv) 165 { 166 struct sshbuf *b; 167 Options options; 168 #define NUM_KEYTYPES 5 169 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 170 struct passwd *pw; 171 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 172 u_char *signature, *data, rver; 173 char *host, *fp; 174 size_t slen, dlen; 175 176 ssh_malloc_init(); /* must be called before any mallocs */ 177 if (pledge("stdio rpath getpw dns id", NULL) != 0) 178 fatal("%s: pledge: %s", __progname, strerror(errno)); 179 180 /* Ensure that stdin and stdout are connected */ 181 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 182 exit(1); 183 /* Leave /dev/null fd iff it is attached to stderr */ 184 if (fd > 2) 185 close(fd); 186 187 i = 0; 188 /* XXX This really needs to read sshd_config for the paths */ 189 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 190 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 191 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 192 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 193 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 194 195 if ((pw = getpwuid(getuid())) == NULL) 196 fatal("getpwuid failed"); 197 pw = pwcopy(pw); 198 199 permanently_set_uid(pw); 200 201 seed_rng(); 202 203 #ifdef DEBUG_SSH_KEYSIGN 204 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 205 #endif 206 207 /* verify that ssh-keysign is enabled by the admin */ 208 initialize_options(&options); 209 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 210 &options, 0, NULL); 211 fill_default_options(&options); 212 if (options.enable_ssh_keysign != 1) 213 fatal("ssh-keysign not enabled in %s", 214 _PATH_HOST_CONFIG_FILE); 215 216 for (i = found = 0; i < NUM_KEYTYPES; i++) { 217 if (key_fd[i] != -1) 218 found = 1; 219 } 220 if (found == 0) 221 fatal("could not open any host key"); 222 223 found = 0; 224 for (i = 0; i < NUM_KEYTYPES; i++) { 225 keys[i] = NULL; 226 if (key_fd[i] == -1) 227 continue; 228 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 229 NULL, &key, NULL); 230 close(key_fd[i]); 231 if (r != 0) 232 debug("parse key %d: %s", i, ssh_err(r)); 233 else if (key != NULL) { 234 keys[i] = key; 235 found = 1; 236 } 237 } 238 if (!found) 239 fatal("no hostkey found"); 240 241 if (pledge("stdio dns", NULL) != 0) 242 fatal("%s: pledge: %s", __progname, strerror(errno)); 243 244 if ((b = sshbuf_new()) == NULL) 245 fatal("%s: sshbuf_new failed", __progname); 246 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 247 fatal("ssh_msg_recv failed"); 248 if ((r = sshbuf_get_u8(b, &rver)) != 0) 249 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 250 if (rver != version) 251 fatal("bad version: received %d, expected %d", rver, version); 252 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 253 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 254 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 255 fatal("bad fd"); 256 if ((host = get_local_name(fd)) == NULL) 257 fatal("cannot get local name for fd"); 258 259 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 260 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 261 if (valid_request(pw, host, &key, data, dlen) < 0) 262 fatal("not a valid request"); 263 free(host); 264 265 found = 0; 266 for (i = 0; i < NUM_KEYTYPES; i++) { 267 if (keys[i] != NULL && 268 sshkey_equal_public(key, keys[i])) { 269 found = 1; 270 break; 271 } 272 } 273 if (!found) { 274 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 275 SSH_FP_DEFAULT)) == NULL) 276 fatal("%s: sshkey_fingerprint failed", __progname); 277 fatal("no matching hostkey found for key %s %s", 278 sshkey_type(key), fp ? fp : ""); 279 } 280 281 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0)) 282 != 0) 283 fatal("sshkey_sign failed: %s", ssh_err(r)); 284 free(data); 285 286 /* send reply */ 287 sshbuf_reset(b); 288 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 289 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 290 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 291 fatal("ssh_msg_send failed"); 292 293 return (0); 294 } 295