1 /* $NetBSD: ssh-keysign.c,v 1.23 2022/02/23 19:07:20 christos Exp $ */ 2 /* $OpenBSD: ssh-keysign.c,v 1.70 2022/01/06 22:00:18 djm 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 1.23 2022/02/23 19:07:20 christos Exp $"); 29 #include <sys/types.h> 30 31 #ifdef WITH_OPENSSL 32 #include <openssl/evp.h> 33 #endif 34 35 #include <fcntl.h> 36 #include <paths.h> 37 #include <pwd.h> 38 #include <stdarg.h> 39 #include <stdio.h> 40 #include <stdlib.h> 41 #include <string.h> 42 #include <unistd.h> 43 #include <errno.h> 44 45 #include "xmalloc.h" 46 #include "log.h" 47 #include "sshkey.h" 48 #include "ssh.h" 49 #include "ssh2.h" 50 #include "misc.h" 51 #include "sshbuf.h" 52 #include "authfile.h" 53 #include "msg.h" 54 #include "canohost.h" 55 #include "pathnames.h" 56 #include "readconf.h" 57 #include "uidswap.h" 58 #include "ssherr.h" 59 60 extern char *__progname; 61 62 static int 63 valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp, 64 u_char *data, size_t datalen) 65 { 66 struct sshbuf *b; 67 struct sshkey *key = NULL; 68 u_char type, *pkblob; 69 char *p; 70 size_t blen, len; 71 char *pkalg, *luser; 72 int r, pktype, fail; 73 74 if (ret != NULL) 75 *ret = NULL; 76 if (pkalgp != NULL) 77 *pkalgp = NULL; 78 fail = 0; 79 80 if ((b = sshbuf_from(data, datalen)) == NULL) 81 fatal_f("sshbuf_from failed"); 82 83 /* session id */ 84 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 85 fatal_fr(r, "parse session ID"); 86 if (len != 20 && /* SHA1 */ 87 len != 32 && /* SHA256 */ 88 len != 48 && /* SHA384 */ 89 len != 64) /* SHA512 */ 90 fail++; 91 92 if ((r = sshbuf_get_u8(b, &type)) != 0) 93 fatal_fr(r, "parse type"); 94 if (type != SSH2_MSG_USERAUTH_REQUEST) 95 fail++; 96 97 /* server user */ 98 if ((r = sshbuf_skip_string(b)) != 0) 99 fatal_fr(r, "parse user"); 100 101 /* service */ 102 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 103 fatal_fr(r, "parse service"); 104 if (strcmp("ssh-connection", p) != 0) 105 fail++; 106 free(p); 107 108 /* method */ 109 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 110 fatal_fr(r, "parse method"); 111 if (strcmp("hostbased", p) != 0) 112 fail++; 113 free(p); 114 115 /* pubkey */ 116 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 117 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 118 fatal_fr(r, "parse pk"); 119 120 pktype = sshkey_type_from_name(pkalg); 121 if (pktype == KEY_UNSPEC) 122 fail++; 123 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 124 error_fr(r, "decode key"); 125 fail++; 126 } else if (key->type != pktype) 127 fail++; 128 129 /* client host name, handle trailing dot */ 130 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 131 fatal_fr(r, "parse hostname"); 132 debug2_f("check expect chost %s got %s", host, p); 133 if (strlen(host) != len - 1) 134 fail++; 135 else if (p[len - 1] != '.') 136 fail++; 137 else if (strncasecmp(host, p, len - 1) != 0) 138 fail++; 139 free(p); 140 141 /* local user */ 142 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 143 fatal_fr(r, "parse luser"); 144 145 if (strcmp(pw->pw_name, luser) != 0) 146 fail++; 147 free(luser); 148 149 /* end of message */ 150 if (sshbuf_len(b) != 0) 151 fail++; 152 sshbuf_free(b); 153 154 debug3_f("fail %d", fail); 155 156 if (fail) 157 sshkey_free(key); 158 else { 159 if (ret != NULL) { 160 *ret = key; 161 key = NULL; 162 } 163 if (pkalgp != NULL) { 164 *pkalgp = pkalg; 165 pkalg = NULL; 166 } 167 } 168 sshkey_free(key); 169 free(pkalg); 170 free(pkblob); 171 172 return (fail ? -1 : 0); 173 } 174 175 int 176 main(int argc, char **argv) 177 { 178 struct sshbuf *b; 179 Options options; 180 #define NUM_KEYTYPES 5 181 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 182 struct passwd *pw; 183 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 184 u_char *signature, *data, rver; 185 char *host, *fp, *pkalg; 186 size_t slen, dlen; 187 188 #ifdef __OpenBSD__ 189 if (pledge("stdio rpath getpw dns id", NULL) != 0) 190 fatal("%s: pledge: %s", __progname, strerror(errno)); 191 #endif 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 #ifdef DEBUG_SSH_KEYSIGN 215 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 216 #endif 217 218 /* verify that ssh-keysign is enabled by the admin */ 219 initialize_options(&options); 220 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 221 &options, 0, NULL); 222 (void)fill_default_options(&options); 223 if (options.enable_ssh_keysign != 1) 224 fatal("ssh-keysign not enabled in %s", 225 _PATH_HOST_CONFIG_FILE); 226 227 #ifdef __OpenBSD__ 228 if (pledge("stdio dns", NULL) != 0) 229 fatal("%s: pledge: %s", __progname, strerror(errno)); 230 #endif 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 #ifdef WITH_OPENSSL 240 OpenSSL_add_all_algorithms(); 241 #endif 242 243 found = 0; 244 for (i = 0; i < NUM_KEYTYPES; i++) { 245 keys[i] = NULL; 246 if (key_fd[i] == -1) 247 continue; 248 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 249 NULL, &key, NULL); 250 close(key_fd[i]); 251 if (r != 0) 252 debug_r(r, "parse key %d", i); 253 else if (key != NULL) { 254 keys[i] = key; 255 found = 1; 256 } 257 } 258 if (!found) 259 fatal("no hostkey found"); 260 261 if ((b = sshbuf_new()) == NULL) 262 fatal("%s: sshbuf_new failed", __progname); 263 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 264 fatal("%s: ssh_msg_recv failed", __progname); 265 if ((r = sshbuf_get_u8(b, &rver)) != 0) 266 fatal_r(r, "%s: buffer error", __progname); 267 if (rver != version) 268 fatal("%s: bad version: received %d, expected %d", 269 __progname, rver, version); 270 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 271 fatal_r(r, "%s: buffer error", __progname); 272 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 273 fatal("%s: bad fd = %d", __progname, fd); 274 if ((host = get_local_name(fd)) == NULL) 275 fatal("%s: cannot get local name for fd", __progname); 276 277 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 278 fatal_r(r, "%s: buffer error", __progname); 279 if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0) 280 fatal("%s: not a valid request", __progname); 281 free(host); 282 283 found = 0; 284 for (i = 0; i < NUM_KEYTYPES; i++) { 285 if (keys[i] != NULL && 286 sshkey_equal_public(key, keys[i])) { 287 found = 1; 288 break; 289 } 290 } 291 if (!found) { 292 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 293 SSH_FP_DEFAULT)) == NULL) 294 fatal("%s: sshkey_fingerprint failed", __progname); 295 fatal("%s: no matching hostkey found for key %s %s", __progname, 296 sshkey_type(key), fp ? fp : ""); 297 } 298 299 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 300 pkalg, NULL, NULL, 0)) != 0) 301 fatal_r(r, "%s: sshkey_sign failed", __progname); 302 free(data); 303 304 /* send reply */ 305 sshbuf_reset(b); 306 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 307 fatal_r(r, "%s: buffer error", __progname); 308 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 309 fatal("%s: ssh_msg_send failed", __progname); 310 311 return (0); 312 } 313