1 /* $NetBSD: ssh-keysign.c,v 1.12 2016/12/25 00:07:47 christos Exp $ */ 2 /* $OpenBSD: ssh-keysign.c,v 1.52 2016/02/15 09:47:49 dtucker Exp $ */ 3 4 /* 5 * Copyright (c) 2002 Markus Friedl. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #include "includes.h" 29 __RCSID("$NetBSD: ssh-keysign.c,v 1.12 2016/12/25 00:07:47 christos Exp $"); 30 #include <sys/types.h> 31 32 #include <openssl/evp.h> 33 #include <openssl/rsa.h> 34 35 #include <fcntl.h> 36 #include <paths.h> 37 #include <pwd.h> 38 #include <stdlib.h> 39 #include <string.h> 40 #include <unistd.h> 41 #include <errno.h> 42 43 #include "xmalloc.h" 44 #include "log.h" 45 #include "sshkey.h" 46 #include "ssh.h" 47 #include "ssh2.h" 48 #include "misc.h" 49 #include "sshbuf.h" 50 #include "authfile.h" 51 #include "msg.h" 52 #include "canohost.h" 53 #include "pathnames.h" 54 #include "readconf.h" 55 #include "uidswap.h" 56 #include "sshkey.h" 57 #include "ssherr.h" 58 59 extern char *__progname; 60 61 /* XXX readconf.c needs these */ 62 uid_t original_real_uid; 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 && key != NULL) 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 4 169 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 #ifdef __OpenBSD__ 178 if (pledge("stdio rpath getpw dns id", NULL) != 0) 179 fatal("%s: pledge: %s", __progname, strerror(errno)); 180 #endif 181 182 /* Ensure that stdin and stdout are connected */ 183 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 184 exit(1); 185 /* Leave /dev/null fd iff it is attached to stderr */ 186 if (fd > 2) 187 close(fd); 188 189 i = 0; 190 /* XXX This really needs to read sshd_config for the paths */ 191 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 192 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 193 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 194 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 195 196 original_real_uid = getuid(); /* XXX readconf.c needs this */ 197 if ((pw = getpwuid(original_real_uid)) == NULL) 198 fatal("getpwuid failed"); 199 pw = pwcopy(pw); 200 201 permanently_set_uid(pw); 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, "", "", &options, 0); 210 fill_default_options(&options); 211 if (options.enable_ssh_keysign != 1) 212 fatal("ssh-keysign not enabled in %s", 213 _PATH_HOST_CONFIG_FILE); 214 215 for (i = found = 0; i < NUM_KEYTYPES; i++) { 216 if (key_fd[i] != -1) 217 found = 1; 218 } 219 if (found == 0) 220 fatal("could not open any host key"); 221 222 OpenSSL_add_all_algorithms(); 223 224 found = 0; 225 for (i = 0; i < NUM_KEYTYPES; i++) { 226 keys[i] = NULL; 227 if (key_fd[i] == -1) 228 continue; 229 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 230 NULL, &key, NULL); 231 close(key_fd[i]); 232 if (r != 0) 233 debug("parse key %d: %s", i, ssh_err(r)); 234 else if (key != NULL) { 235 keys[i] = key; 236 found = 1; 237 } 238 } 239 if (!found) 240 fatal("no hostkey found"); 241 242 #ifdef __OpenBSD__ 243 if (pledge("stdio dns", NULL) != 0) 244 fatal("%s: pledge: %s", __progname, strerror(errno)); 245 #endif 246 247 if ((b = sshbuf_new()) == NULL) 248 fatal("%s: sshbuf_new failed", __progname); 249 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 250 fatal("ssh_msg_recv failed"); 251 if ((r = sshbuf_get_u8(b, &rver)) != 0) 252 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 253 if (rver != version) 254 fatal("bad version: received %d, expected %d", rver, version); 255 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 256 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 257 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 258 fatal("bad fd"); 259 if ((host = get_local_name(fd)) == NULL) 260 fatal("cannot get local name for fd"); 261 262 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 263 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 264 if (valid_request(pw, host, &key, data, dlen) < 0) 265 fatal("not a valid request"); 266 free(host); 267 268 found = 0; 269 for (i = 0; i < NUM_KEYTYPES; i++) { 270 if (keys[i] != NULL && 271 sshkey_equal_public(key, keys[i])) { 272 found = 1; 273 break; 274 } 275 } 276 if (!found) { 277 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 278 SSH_FP_DEFAULT)) == NULL) 279 fatal("%s: sshkey_fingerprint failed", __progname); 280 fatal("no matching hostkey found for key %s %s", 281 sshkey_type(key), fp ? fp : ""); 282 } 283 284 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0)) 285 != 0) 286 fatal("sshkey_sign failed: %s", ssh_err(r)); 287 free(data); 288 289 /* send reply */ 290 sshbuf_reset(b); 291 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 292 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 293 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 294 fatal("ssh_msg_send failed"); 295 296 return (0); 297 } 298