1 /* $OpenBSD: ssh-keysign.c,v 1.70 2022/01/06 22:00:18 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 <stdio.h> 35 #include <stdlib.h> 36 #include <string.h> 37 #include <unistd.h> 38 #include <errno.h> 39 40 #ifdef WITH_OPENSSL 41 #include <openssl/evp.h> 42 #include <openssl/rand.h> 43 #include <openssl/rsa.h> 44 #include "openbsd-compat/openssl-compat.h" 45 #endif 46 47 #include "xmalloc.h" 48 #include "log.h" 49 #include "sshkey.h" 50 #include "ssh.h" 51 #include "ssh2.h" 52 #include "misc.h" 53 #include "sshbuf.h" 54 #include "authfile.h" 55 #include "msg.h" 56 #include "canohost.h" 57 #include "pathnames.h" 58 #include "readconf.h" 59 #include "uidswap.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, char **pkalgp, 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 if (pkalgp != NULL) 79 *pkalgp = NULL; 80 fail = 0; 81 82 if ((b = sshbuf_from(data, datalen)) == NULL) 83 fatal_f("sshbuf_from failed"); 84 85 /* session id */ 86 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 87 fatal_fr(r, "parse session ID"); 88 if (len != 20 && /* SHA1 */ 89 len != 32 && /* SHA256 */ 90 len != 48 && /* SHA384 */ 91 len != 64) /* SHA512 */ 92 fail++; 93 94 if ((r = sshbuf_get_u8(b, &type)) != 0) 95 fatal_fr(r, "parse type"); 96 if (type != SSH2_MSG_USERAUTH_REQUEST) 97 fail++; 98 99 /* server user */ 100 if ((r = sshbuf_skip_string(b)) != 0) 101 fatal_fr(r, "parse user"); 102 103 /* service */ 104 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 105 fatal_fr(r, "parse service"); 106 if (strcmp("ssh-connection", p) != 0) 107 fail++; 108 free(p); 109 110 /* method */ 111 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 112 fatal_fr(r, "parse method"); 113 if (strcmp("hostbased", p) != 0) 114 fail++; 115 free(p); 116 117 /* pubkey */ 118 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 119 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 120 fatal_fr(r, "parse pk"); 121 122 pktype = sshkey_type_from_name(pkalg); 123 if (pktype == KEY_UNSPEC) 124 fail++; 125 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 126 error_fr(r, "decode key"); 127 fail++; 128 } else if (key->type != pktype) 129 fail++; 130 131 /* client host name, handle trailing dot */ 132 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 133 fatal_fr(r, "parse hostname"); 134 debug2_f("check expect chost %s got %s", host, p); 135 if (strlen(host) != len - 1) 136 fail++; 137 else if (p[len - 1] != '.') 138 fail++; 139 else if (strncasecmp(host, p, len - 1) != 0) 140 fail++; 141 free(p); 142 143 /* local user */ 144 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 145 fatal_fr(r, "parse luser"); 146 147 if (strcmp(pw->pw_name, luser) != 0) 148 fail++; 149 free(luser); 150 151 /* end of message */ 152 if (sshbuf_len(b) != 0) 153 fail++; 154 sshbuf_free(b); 155 156 debug3_f("fail %d", fail); 157 158 if (fail) 159 sshkey_free(key); 160 else { 161 if (ret != NULL) { 162 *ret = key; 163 key = NULL; 164 } 165 if (pkalgp != NULL) { 166 *pkalgp = pkalg; 167 pkalg = NULL; 168 } 169 } 170 sshkey_free(key); 171 free(pkalg); 172 free(pkblob); 173 174 return (fail ? -1 : 0); 175 } 176 177 int 178 main(int argc, char **argv) 179 { 180 struct sshbuf *b; 181 Options options; 182 #define NUM_KEYTYPES 5 183 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 184 struct passwd *pw; 185 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 186 u_char *signature, *data, rver; 187 char *host, *fp, *pkalg; 188 size_t slen, dlen; 189 190 if (pledge("stdio rpath getpw dns id", NULL) != 0) 191 fatal("%s: pledge: %s", __progname, strerror(errno)); 192 193 /* Ensure that stdin and stdout are connected */ 194 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 195 exit(1); 196 /* Leave /dev/null fd iff it is attached to stderr */ 197 if (fd > 2) 198 close(fd); 199 200 i = 0; 201 /* XXX This really needs to read sshd_config for the paths */ 202 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 203 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 204 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 205 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 206 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 207 208 if ((pw = getpwuid(getuid())) == NULL) 209 fatal("getpwuid failed"); 210 pw = pwcopy(pw); 211 212 permanently_set_uid(pw); 213 214 seed_rng(); 215 216 #ifdef DEBUG_SSH_KEYSIGN 217 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 218 #endif 219 220 /* verify that ssh-keysign is enabled by the admin */ 221 initialize_options(&options); 222 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 223 &options, 0, NULL); 224 (void)fill_default_options(&options); 225 if (options.enable_ssh_keysign != 1) 226 fatal("ssh-keysign not enabled in %s", 227 _PATH_HOST_CONFIG_FILE); 228 229 if (pledge("stdio dns", NULL) != 0) 230 fatal("%s: pledge: %s", __progname, strerror(errno)); 231 232 for (i = found = 0; i < NUM_KEYTYPES; i++) { 233 if (key_fd[i] != -1) 234 found = 1; 235 } 236 if (found == 0) 237 fatal("could not open any host key"); 238 239 found = 0; 240 for (i = 0; i < NUM_KEYTYPES; i++) { 241 keys[i] = NULL; 242 if (key_fd[i] == -1) 243 continue; 244 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 245 NULL, &key, NULL); 246 close(key_fd[i]); 247 if (r != 0) 248 debug_r(r, "parse key %d", i); 249 else if (key != NULL) { 250 keys[i] = key; 251 found = 1; 252 } 253 } 254 if (!found) 255 fatal("no hostkey found"); 256 257 if ((b = sshbuf_new()) == NULL) 258 fatal("%s: sshbuf_new failed", __progname); 259 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 260 fatal("%s: ssh_msg_recv failed", __progname); 261 if ((r = sshbuf_get_u8(b, &rver)) != 0) 262 fatal_r(r, "%s: buffer error", __progname); 263 if (rver != version) 264 fatal("%s: bad version: received %d, expected %d", 265 __progname, rver, version); 266 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 267 fatal_r(r, "%s: buffer error", __progname); 268 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 269 fatal("%s: bad fd = %d", __progname, fd); 270 if ((host = get_local_name(fd)) == NULL) 271 fatal("%s: cannot get local name for fd", __progname); 272 273 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 274 fatal_r(r, "%s: buffer error", __progname); 275 if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0) 276 fatal("%s: not a valid request", __progname); 277 free(host); 278 279 found = 0; 280 for (i = 0; i < NUM_KEYTYPES; i++) { 281 if (keys[i] != NULL && 282 sshkey_equal_public(key, keys[i])) { 283 found = 1; 284 break; 285 } 286 } 287 if (!found) { 288 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 289 SSH_FP_DEFAULT)) == NULL) 290 fatal("%s: sshkey_fingerprint failed", __progname); 291 fatal("%s: no matching hostkey found for key %s %s", __progname, 292 sshkey_type(key), fp ? fp : ""); 293 } 294 295 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 296 pkalg, NULL, NULL, 0)) != 0) 297 fatal_r(r, "%s: sshkey_sign failed", __progname); 298 free(data); 299 300 /* send reply */ 301 sshbuf_reset(b); 302 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 303 fatal_r(r, "%s: buffer error", __progname); 304 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 305 fatal("%s: ssh_msg_send failed", __progname); 306 307 return (0); 308 } 309