1 /* $OpenBSD: ssh-keysign.c,v 1.67 2021/07/05 01:16:46 dtucker 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, 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 fail = 0; 79 80 if ((b = sshbuf_from(data, datalen)) == NULL) 81 fatal_f("sshbuf_from failed"); 82 83 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 84 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 85 fatal_fr(r, "parse session ID"); 86 if (len != 20 && len != 32) 87 fail++; 88 89 if ((r = sshbuf_get_u8(b, &type)) != 0) 90 fatal_fr(r, "parse type"); 91 if (type != SSH2_MSG_USERAUTH_REQUEST) 92 fail++; 93 94 /* server user */ 95 if ((r = sshbuf_skip_string(b)) != 0) 96 fatal_fr(r, "parse user"); 97 98 /* service */ 99 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 100 fatal_fr(r, "parse service"); 101 if (strcmp("ssh-connection", p) != 0) 102 fail++; 103 free(p); 104 105 /* method */ 106 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 107 fatal_fr(r, "parse method"); 108 if (strcmp("hostbased", p) != 0) 109 fail++; 110 free(p); 111 112 /* pubkey */ 113 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 114 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 115 fatal_fr(r, "parse pk"); 116 117 pktype = sshkey_type_from_name(pkalg); 118 if (pktype == KEY_UNSPEC) 119 fail++; 120 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 121 error_fr(r, "decode key"); 122 fail++; 123 } else if (key->type != pktype) 124 fail++; 125 free(pkalg); 126 free(pkblob); 127 128 /* client host name, handle trailing dot */ 129 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 130 fatal_fr(r, "parse hostname"); 131 debug2_f("check expect chost %s got %s", host, p); 132 if (strlen(host) != len - 1) 133 fail++; 134 else if (p[len - 1] != '.') 135 fail++; 136 else if (strncasecmp(host, p, len - 1) != 0) 137 fail++; 138 free(p); 139 140 /* local user */ 141 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 142 fatal_fr(r, "parse luser"); 143 144 if (strcmp(pw->pw_name, luser) != 0) 145 fail++; 146 free(luser); 147 148 /* end of message */ 149 if (sshbuf_len(b) != 0) 150 fail++; 151 sshbuf_free(b); 152 153 debug3_f("fail %d", fail); 154 155 if (fail) 156 sshkey_free(key); 157 else if (ret != NULL) 158 *ret = key; 159 160 return (fail ? -1 : 0); 161 } 162 163 int 164 main(int argc, char **argv) 165 { 166 struct sshbuf *b; 167 Options options; 168 #define NUM_KEYTYPES 5 169 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 170 struct passwd *pw; 171 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 172 u_char *signature, *data, rver; 173 char *host, *fp; 174 size_t slen, dlen; 175 176 if (pledge("stdio rpath getpw dns id", NULL) != 0) 177 fatal("%s: pledge: %s", __progname, strerror(errno)); 178 179 /* Ensure that stdin and stdout are connected */ 180 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 181 exit(1); 182 /* Leave /dev/null fd iff it is attached to stderr */ 183 if (fd > 2) 184 close(fd); 185 186 i = 0; 187 /* XXX This really needs to read sshd_config for the paths */ 188 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 189 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 190 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 191 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 192 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 193 194 if ((pw = getpwuid(getuid())) == NULL) 195 fatal("getpwuid failed"); 196 pw = pwcopy(pw); 197 198 permanently_set_uid(pw); 199 200 seed_rng(); 201 202 #ifdef DEBUG_SSH_KEYSIGN 203 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 204 #endif 205 206 /* verify that ssh-keysign is enabled by the admin */ 207 initialize_options(&options); 208 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 209 &options, 0, NULL); 210 (void)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 found = 0; 223 for (i = 0; i < NUM_KEYTYPES; i++) { 224 keys[i] = NULL; 225 if (key_fd[i] == -1) 226 continue; 227 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 228 NULL, &key, NULL); 229 close(key_fd[i]); 230 if (r != 0) 231 debug_r(r, "parse key %d", i); 232 else if (key != NULL) { 233 keys[i] = key; 234 found = 1; 235 } 236 } 237 if (!found) 238 fatal("no hostkey found"); 239 240 if (pledge("stdio dns", NULL) != 0) 241 fatal("%s: pledge: %s", __progname, strerror(errno)); 242 243 if ((b = sshbuf_new()) == NULL) 244 fatal("%s: sshbuf_new failed", __progname); 245 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 246 fatal("%s: ssh_msg_recv failed", __progname); 247 if ((r = sshbuf_get_u8(b, &rver)) != 0) 248 fatal_r(r, "%s: buffer error", __progname); 249 if (rver != version) 250 fatal("%s: bad version: received %d, expected %d", 251 __progname, rver, version); 252 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 253 fatal_r(r, "%s: buffer error", __progname); 254 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 255 fatal("%s: bad fd = %d", __progname, fd); 256 if ((host = get_local_name(fd)) == NULL) 257 fatal("%s: cannot get local name for fd", __progname); 258 259 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 260 fatal_r(r, "%s: buffer error", __progname); 261 if (valid_request(pw, host, &key, data, dlen) < 0) 262 fatal("%s: not a valid request", __progname); 263 free(host); 264 265 found = 0; 266 for (i = 0; i < NUM_KEYTYPES; i++) { 267 if (keys[i] != NULL && 268 sshkey_equal_public(key, keys[i])) { 269 found = 1; 270 break; 271 } 272 } 273 if (!found) { 274 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 275 SSH_FP_DEFAULT)) == NULL) 276 fatal("%s: sshkey_fingerprint failed", __progname); 277 fatal("%s: no matching hostkey found for key %s %s", __progname, 278 sshkey_type(key), fp ? fp : ""); 279 } 280 281 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 282 NULL, NULL, NULL, 0)) != 0) 283 fatal_r(r, "%s: sshkey_sign failed", __progname); 284 free(data); 285 286 /* send reply */ 287 sshbuf_reset(b); 288 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 289 fatal_r(r, "%s: buffer error", __progname); 290 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 291 fatal("%s: ssh_msg_send failed", __progname); 292 293 return (0); 294 } 295