1 /* $NetBSD: ssh-keysign.c,v 1.14 2018/04/06 18:59:00 christos Exp $ */ 2 /* $OpenBSD: ssh-keysign.c,v 1.54 2018/02/23 15:58:38 markus Exp $ */ 3 /* 4 * Copyright (c) 2002 Markus Friedl. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include "includes.h" 28 __RCSID("$NetBSD: ssh-keysign.c,v 1.14 2018/04/06 18:59:00 christos Exp $"); 29 #include <sys/types.h> 30 31 #include <openssl/evp.h> 32 #include <openssl/rsa.h> 33 34 #include <fcntl.h> 35 #include <paths.h> 36 #include <pwd.h> 37 #include <stdlib.h> 38 #include <string.h> 39 #include <unistd.h> 40 #include <errno.h> 41 42 #include "xmalloc.h" 43 #include "log.h" 44 #include "sshkey.h" 45 #include "ssh.h" 46 #include "ssh2.h" 47 #include "misc.h" 48 #include "sshbuf.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 #include "sshkey.h" 56 #include "ssherr.h" 57 58 extern char *__progname; 59 60 /* XXX readconf.c needs these */ 61 uid_t original_real_uid; 62 63 static int 64 valid_request(struct passwd *pw, char *host, struct sshkey **ret, 65 u_char *data, size_t datalen) 66 { 67 struct sshbuf *b; 68 struct sshkey *key = NULL; 69 u_char type, *pkblob; 70 char *p; 71 size_t blen, len; 72 char *pkalg, *luser; 73 int r, pktype, fail; 74 75 if (ret != NULL) 76 *ret = NULL; 77 fail = 0; 78 79 if ((b = sshbuf_from(data, datalen)) == NULL) 80 fatal("%s: sshbuf_from failed", __func__); 81 82 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 83 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 84 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 85 if (len != 20 && len != 32) 86 fail++; 87 88 if ((r = sshbuf_get_u8(b, &type)) != 0) 89 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 90 if (type != SSH2_MSG_USERAUTH_REQUEST) 91 fail++; 92 93 /* server user */ 94 if ((r = sshbuf_skip_string(b)) != 0) 95 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 96 97 /* service */ 98 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 99 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 100 if (strcmp("ssh-connection", p) != 0) 101 fail++; 102 free(p); 103 104 /* method */ 105 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 106 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 107 if (strcmp("hostbased", p) != 0) 108 fail++; 109 free(p); 110 111 /* pubkey */ 112 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 113 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 114 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 115 116 pktype = sshkey_type_from_name(pkalg); 117 if (pktype == KEY_UNSPEC) 118 fail++; 119 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 120 error("%s: bad key blob: %s", __func__, ssh_err(r)); 121 fail++; 122 } else if (key->type != pktype) 123 fail++; 124 free(pkalg); 125 free(pkblob); 126 127 /* client host name, handle trailing dot */ 128 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 129 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 130 debug2("%s: check expect chost %s got %s", __func__, host, p); 131 if (strlen(host) != len - 1) 132 fail++; 133 else if (p[len - 1] != '.') 134 fail++; 135 else if (strncasecmp(host, p, len - 1) != 0) 136 fail++; 137 free(p); 138 139 /* local user */ 140 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 141 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 142 143 if (strcmp(pw->pw_name, luser) != 0) 144 fail++; 145 free(luser); 146 147 /* end of message */ 148 if (sshbuf_len(b) != 0) 149 fail++; 150 sshbuf_free(b); 151 152 debug3("%s: fail %d", __func__, fail); 153 154 if (fail) 155 sshkey_free(key); 156 else if (ret != NULL) 157 *ret = key; 158 159 return (fail ? -1 : 0); 160 } 161 162 int 163 main(int argc, char **argv) 164 { 165 struct sshbuf *b; 166 Options options; 167 #define NUM_KEYTYPES 5 168 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 169 struct passwd *pw; 170 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 171 u_char *signature, *data, rver; 172 char *host, *fp; 173 size_t slen, dlen; 174 175 ssh_malloc_init(); /* must be called before any mallocs */ 176 #ifdef __OpenBSD__ 177 if (pledge("stdio rpath getpw dns id", NULL) != 0) 178 fatal("%s: pledge: %s", __progname, strerror(errno)); 179 #endif 180 181 /* Ensure that stdin and stdout are connected */ 182 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 183 exit(1); 184 /* Leave /dev/null fd iff it is attached to stderr */ 185 if (fd > 2) 186 close(fd); 187 188 i = 0; 189 /* XXX This really needs to read sshd_config for the paths */ 190 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 191 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 192 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 193 key_fd[i++] = open(_PATH_HOST_XMSS_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