1 /* $OpenBSD: ssh-keysign.c,v 1.73 2024/01/11 01:51:16 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 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 if (pledge("stdio rpath getpw dns id", NULL) != 0) 189 fatal("%s: pledge: %s", __progname, strerror(errno)); 190 191 /* Ensure that stdin and stdout are connected */ 192 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 193 exit(1); 194 /* Leave /dev/null fd iff it is attached to stderr */ 195 if (fd > 2) 196 close(fd); 197 198 for (i = 0; i < NUM_KEYTYPES; i++) 199 key_fd[i] = -1; 200 201 i = 0; 202 /* XXX This really needs to read sshd_config for the paths */ 203 #ifdef WITH_DSA 204 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 205 #endif 206 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 207 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 208 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 209 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 210 211 if ((pw = getpwuid(getuid())) == NULL) 212 fatal("getpwuid failed"); 213 pw = pwcopy(pw); 214 215 permanently_set_uid(pw); 216 217 seed_rng(); 218 219 #ifdef DEBUG_SSH_KEYSIGN 220 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 221 #endif 222 223 /* verify that ssh-keysign is enabled by the admin */ 224 initialize_options(&options); 225 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 226 &options, 0, NULL); 227 (void)fill_default_options(&options); 228 if (options.enable_ssh_keysign != 1) 229 fatal("ssh-keysign not enabled in %s", 230 _PATH_HOST_CONFIG_FILE); 231 232 if (pledge("stdio dns", NULL) != 0) 233 fatal("%s: pledge: %s", __progname, strerror(errno)); 234 235 for (i = found = 0; i < NUM_KEYTYPES; i++) { 236 if (key_fd[i] != -1) 237 found = 1; 238 } 239 if (found == 0) 240 fatal("could not open any host key"); 241 242 found = 0; 243 for (i = 0; i < NUM_KEYTYPES; i++) { 244 keys[i] = NULL; 245 if (key_fd[i] == -1) 246 continue; 247 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 248 NULL, &key, NULL); 249 close(key_fd[i]); 250 if (r != 0) 251 debug_r(r, "parse key %d", i); 252 else if (key != NULL) { 253 keys[i] = key; 254 found = 1; 255 } 256 } 257 if (!found) 258 fatal("no hostkey found"); 259 260 if ((b = sshbuf_new()) == NULL) 261 fatal("%s: sshbuf_new failed", __progname); 262 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 263 fatal("%s: ssh_msg_recv failed", __progname); 264 if ((r = sshbuf_get_u8(b, &rver)) != 0) 265 fatal_r(r, "%s: buffer error", __progname); 266 if (rver != version) 267 fatal("%s: bad version: received %d, expected %d", 268 __progname, rver, version); 269 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 270 fatal_r(r, "%s: buffer error", __progname); 271 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 272 fatal("%s: bad fd = %d", __progname, fd); 273 if ((host = get_local_name(fd)) == NULL) 274 fatal("%s: cannot get local name for fd", __progname); 275 276 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 277 fatal_r(r, "%s: buffer error", __progname); 278 if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0) 279 fatal("%s: not a valid request", __progname); 280 free(host); 281 282 found = 0; 283 for (i = 0; i < NUM_KEYTYPES; i++) { 284 if (keys[i] != NULL && 285 sshkey_equal_public(key, keys[i])) { 286 found = 1; 287 break; 288 } 289 } 290 if (!found) { 291 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 292 SSH_FP_DEFAULT)) == NULL) 293 fatal("%s: sshkey_fingerprint failed", __progname); 294 fatal("%s: no matching hostkey found for key %s %s", __progname, 295 sshkey_type(key), fp ? fp : ""); 296 } 297 298 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 299 pkalg, NULL, NULL, 0)) != 0) 300 fatal_r(r, "%s: sshkey_sign failed", __progname); 301 free(data); 302 303 /* send reply */ 304 sshbuf_reset(b); 305 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 306 fatal_r(r, "%s: buffer error", __progname); 307 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 308 fatal("%s: ssh_msg_send failed", __progname); 309 310 return (0); 311 } 312