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 <sys/types.h> 27 28 #include <openssl/evp.h> 29 #include <openssl/rsa.h> 30 31 #include <fcntl.h> 32 #include <paths.h> 33 #include <pwd.h> 34 #include <stdlib.h> 35 #include <string.h> 36 #include <unistd.h> 37 #include <errno.h> 38 39 #include "xmalloc.h" 40 #include "log.h" 41 #include "sshkey.h" 42 #include "ssh.h" 43 #include "ssh2.h" 44 #include "misc.h" 45 #include "sshbuf.h" 46 #include "authfile.h" 47 #include "msg.h" 48 #include "canohost.h" 49 #include "pathnames.h" 50 #include "readconf.h" 51 #include "uidswap.h" 52 #include "sshkey.h" 53 #include "ssherr.h" 54 55 extern char *__progname; 56 57 static int 58 valid_request(struct passwd *pw, char *host, struct sshkey **ret, 59 u_char *data, size_t datalen) 60 { 61 struct sshbuf *b; 62 struct sshkey *key = NULL; 63 u_char type, *pkblob; 64 char *p; 65 size_t blen, len; 66 char *pkalg, *luser; 67 int r, pktype, fail; 68 69 if (ret != NULL) 70 *ret = NULL; 71 fail = 0; 72 73 if ((b = sshbuf_from(data, datalen)) == NULL) 74 fatal("%s: sshbuf_from failed", __func__); 75 76 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 77 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 78 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 79 if (len != 20 && len != 32) 80 fail++; 81 82 if ((r = sshbuf_get_u8(b, &type)) != 0) 83 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 84 if (type != SSH2_MSG_USERAUTH_REQUEST) 85 fail++; 86 87 /* server user */ 88 if ((r = sshbuf_skip_string(b)) != 0) 89 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 90 91 /* service */ 92 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 93 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 94 if (strcmp("ssh-connection", p) != 0) 95 fail++; 96 free(p); 97 98 /* method */ 99 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 100 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 101 if (strcmp("hostbased", p) != 0) 102 fail++; 103 free(p); 104 105 /* pubkey */ 106 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 107 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 108 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 109 110 pktype = sshkey_type_from_name(pkalg); 111 if (pktype == KEY_UNSPEC) 112 fail++; 113 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 114 error("%s: bad key blob: %s", __func__, ssh_err(r)); 115 fail++; 116 } else if (key->type != pktype) 117 fail++; 118 free(pkalg); 119 free(pkblob); 120 121 /* client host name, handle trailing dot */ 122 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 123 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 124 debug2("%s: check expect chost %s got %s", __func__, host, p); 125 if (strlen(host) != len - 1) 126 fail++; 127 else if (p[len - 1] != '.') 128 fail++; 129 else if (strncasecmp(host, p, len - 1) != 0) 130 fail++; 131 free(p); 132 133 /* local user */ 134 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 135 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 136 137 if (strcmp(pw->pw_name, luser) != 0) 138 fail++; 139 free(luser); 140 141 /* end of message */ 142 if (sshbuf_len(b) != 0) 143 fail++; 144 sshbuf_free(b); 145 146 debug3("%s: fail %d", __func__, fail); 147 148 if (fail) 149 sshkey_free(key); 150 else if (ret != NULL) 151 *ret = key; 152 153 return (fail ? -1 : 0); 154 } 155 156 int 157 main(int argc, char **argv) 158 { 159 struct sshbuf *b; 160 Options options; 161 #define NUM_KEYTYPES 5 162 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 163 struct passwd *pw; 164 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 165 u_char *signature, *data, rver; 166 char *host, *fp; 167 size_t slen, dlen; 168 169 ssh_malloc_init(); /* must be called before any mallocs */ 170 if (pledge("stdio rpath getpw dns id", NULL) != 0) 171 fatal("%s: pledge: %s", __progname, strerror(errno)); 172 173 /* Ensure that stdin and stdout are connected */ 174 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 175 exit(1); 176 /* Leave /dev/null fd iff it is attached to stderr */ 177 if (fd > 2) 178 close(fd); 179 180 i = 0; 181 /* XXX This really needs to read sshd_config for the paths */ 182 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 183 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 184 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 185 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 186 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 187 188 if ((pw = getpwuid(getuid())) == NULL) 189 fatal("getpwuid failed"); 190 pw = pwcopy(pw); 191 192 permanently_set_uid(pw); 193 194 #ifdef DEBUG_SSH_KEYSIGN 195 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 196 #endif 197 198 /* verify that ssh-keysign is enabled by the admin */ 199 initialize_options(&options); 200 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 201 &options, 0, NULL); 202 fill_default_options(&options); 203 if (options.enable_ssh_keysign != 1) 204 fatal("ssh-keysign not enabled in %s", 205 _PATH_HOST_CONFIG_FILE); 206 207 for (i = found = 0; i < NUM_KEYTYPES; i++) { 208 if (key_fd[i] != -1) 209 found = 1; 210 } 211 if (found == 0) 212 fatal("could not open any host key"); 213 214 OpenSSL_add_all_algorithms(); 215 216 found = 0; 217 for (i = 0; i < NUM_KEYTYPES; i++) { 218 keys[i] = NULL; 219 if (key_fd[i] == -1) 220 continue; 221 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 222 NULL, &key, NULL); 223 close(key_fd[i]); 224 if (r != 0) 225 debug("parse key %d: %s", i, ssh_err(r)); 226 else if (key != NULL) { 227 keys[i] = key; 228 found = 1; 229 } 230 } 231 if (!found) 232 fatal("no hostkey found"); 233 234 if (pledge("stdio dns", NULL) != 0) 235 fatal("%s: pledge: %s", __progname, strerror(errno)); 236 237 if ((b = sshbuf_new()) == NULL) 238 fatal("%s: sshbuf_new failed", __progname); 239 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 240 fatal("ssh_msg_recv failed"); 241 if ((r = sshbuf_get_u8(b, &rver)) != 0) 242 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 243 if (rver != version) 244 fatal("bad version: received %d, expected %d", rver, version); 245 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 246 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 247 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 248 fatal("bad fd"); 249 if ((host = get_local_name(fd)) == NULL) 250 fatal("cannot get local name for fd"); 251 252 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 253 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 254 if (valid_request(pw, host, &key, data, dlen) < 0) 255 fatal("not a valid request"); 256 free(host); 257 258 found = 0; 259 for (i = 0; i < NUM_KEYTYPES; i++) { 260 if (keys[i] != NULL && 261 sshkey_equal_public(key, keys[i])) { 262 found = 1; 263 break; 264 } 265 } 266 if (!found) { 267 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 268 SSH_FP_DEFAULT)) == NULL) 269 fatal("%s: sshkey_fingerprint failed", __progname); 270 fatal("no matching hostkey found for key %s %s", 271 sshkey_type(key), fp ? fp : ""); 272 } 273 274 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0)) 275 != 0) 276 fatal("sshkey_sign failed: %s", ssh_err(r)); 277 free(data); 278 279 /* send reply */ 280 sshbuf_reset(b); 281 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 282 fatal("%s: buffer error: %s", __progname, ssh_err(r)); 283 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 284 fatal("ssh_msg_send failed"); 285 286 return (0); 287 } 288