1 /* $OpenBSD: ssh-keysign.c,v 1.66 2020/12/17 23:10:27 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 #ifdef WITH_OPENSSL 29 #include <openssl/evp.h> 30 #endif 31 32 #include <fcntl.h> 33 #include <paths.h> 34 #include <pwd.h> 35 #include <stdlib.h> 36 #include <stdio.h> 37 #include <string.h> 38 #include <stdarg.h> 39 #include <unistd.h> 40 #include <errno.h> 41 42 #include "xmalloc.h" 43 #include "log.h" 44 #include "sshkey.h" 45 #include "ssh.h" 46 #include "ssh2.h" 47 #include "misc.h" 48 #include "sshbuf.h" 49 #include "authfile.h" 50 #include "msg.h" 51 #include "canohost.h" 52 #include "pathnames.h" 53 #include "readconf.h" 54 #include "uidswap.h" 55 #include "ssherr.h" 56 57 extern char *__progname; 58 59 static int 60 valid_request(struct passwd *pw, char *host, struct sshkey **ret, 61 u_char *data, size_t datalen) 62 { 63 struct sshbuf *b; 64 struct sshkey *key = NULL; 65 u_char type, *pkblob; 66 char *p; 67 size_t blen, len; 68 char *pkalg, *luser; 69 int r, pktype, fail; 70 71 if (ret != NULL) 72 *ret = NULL; 73 fail = 0; 74 75 if ((b = sshbuf_from(data, datalen)) == NULL) 76 fatal_f("sshbuf_from failed"); 77 78 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ 79 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 80 fatal_fr(r, "parse session ID"); 81 if (len != 20 && len != 32) 82 fail++; 83 84 if ((r = sshbuf_get_u8(b, &type)) != 0) 85 fatal_fr(r, "parse type"); 86 if (type != SSH2_MSG_USERAUTH_REQUEST) 87 fail++; 88 89 /* server user */ 90 if ((r = sshbuf_skip_string(b)) != 0) 91 fatal_fr(r, "parse user"); 92 93 /* service */ 94 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 95 fatal_fr(r, "parse service"); 96 if (strcmp("ssh-connection", p) != 0) 97 fail++; 98 free(p); 99 100 /* method */ 101 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 102 fatal_fr(r, "parse method"); 103 if (strcmp("hostbased", p) != 0) 104 fail++; 105 free(p); 106 107 /* pubkey */ 108 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 109 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 110 fatal_fr(r, "parse pk"); 111 112 pktype = sshkey_type_from_name(pkalg); 113 if (pktype == KEY_UNSPEC) 114 fail++; 115 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 116 error_fr(r, "decode key"); 117 fail++; 118 } else if (key->type != pktype) 119 fail++; 120 free(pkalg); 121 free(pkblob); 122 123 /* client host name, handle trailing dot */ 124 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 125 fatal_fr(r, "parse hostname"); 126 debug2_f("check expect chost %s got %s", host, p); 127 if (strlen(host) != len - 1) 128 fail++; 129 else if (p[len - 1] != '.') 130 fail++; 131 else if (strncasecmp(host, p, len - 1) != 0) 132 fail++; 133 free(p); 134 135 /* local user */ 136 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 137 fatal_fr(r, "parse luser"); 138 139 if (strcmp(pw->pw_name, luser) != 0) 140 fail++; 141 free(luser); 142 143 /* end of message */ 144 if (sshbuf_len(b) != 0) 145 fail++; 146 sshbuf_free(b); 147 148 debug3_f("fail %d", fail); 149 150 if (fail) 151 sshkey_free(key); 152 else if (ret != NULL) 153 *ret = key; 154 155 return (fail ? -1 : 0); 156 } 157 158 int 159 main(int argc, char **argv) 160 { 161 struct sshbuf *b; 162 Options options; 163 #define NUM_KEYTYPES 5 164 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 165 struct passwd *pw; 166 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 167 u_char *signature, *data, rver; 168 char *host, *fp; 169 size_t slen, dlen; 170 171 if (pledge("stdio rpath getpw dns id", NULL) != 0) 172 fatal("%s: pledge: %s", __progname, strerror(errno)); 173 174 /* Ensure that stdin and stdout are connected */ 175 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 176 exit(1); 177 /* Leave /dev/null fd iff it is attached to stderr */ 178 if (fd > 2) 179 close(fd); 180 181 i = 0; 182 /* XXX This really needs to read sshd_config for the paths */ 183 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 184 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 185 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 186 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 187 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 188 189 if ((pw = getpwuid(getuid())) == NULL) 190 fatal("getpwuid failed"); 191 pw = pwcopy(pw); 192 193 permanently_set_uid(pw); 194 195 #ifdef DEBUG_SSH_KEYSIGN 196 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 197 #endif 198 199 /* verify that ssh-keysign is enabled by the admin */ 200 initialize_options(&options); 201 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 202 &options, 0, NULL); 203 (void)fill_default_options(&options); 204 if (options.enable_ssh_keysign != 1) 205 fatal("ssh-keysign not enabled in %s", 206 _PATH_HOST_CONFIG_FILE); 207 208 for (i = found = 0; i < NUM_KEYTYPES; i++) { 209 if (key_fd[i] != -1) 210 found = 1; 211 } 212 if (found == 0) 213 fatal("could not open any host key"); 214 215 #ifdef WITH_OPENSSL 216 OpenSSL_add_all_algorithms(); 217 #endif 218 found = 0; 219 for (i = 0; i < NUM_KEYTYPES; i++) { 220 keys[i] = NULL; 221 if (key_fd[i] == -1) 222 continue; 223 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 224 NULL, &key, NULL); 225 close(key_fd[i]); 226 if (r != 0) 227 debug_r(r, "parse key %d", i); 228 else if (key != NULL) { 229 keys[i] = key; 230 found = 1; 231 } 232 } 233 if (!found) 234 fatal("no hostkey found"); 235 236 if (pledge("stdio dns", NULL) != 0) 237 fatal("%s: pledge: %s", __progname, strerror(errno)); 238 239 if ((b = sshbuf_new()) == NULL) 240 fatal("%s: sshbuf_new failed", __progname); 241 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 242 fatal("%s: ssh_msg_recv failed", __progname); 243 if ((r = sshbuf_get_u8(b, &rver)) != 0) 244 fatal_r(r, "%s: buffer error", __progname); 245 if (rver != version) 246 fatal("%s: bad version: received %d, expected %d", 247 __progname, rver, version); 248 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 249 fatal_r(r, "%s: buffer error", __progname); 250 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 251 fatal("%s: bad fd = %d", __progname, fd); 252 if ((host = get_local_name(fd)) == NULL) 253 fatal("%s: cannot get local name for fd", __progname); 254 255 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 256 fatal_r(r, "%s: buffer error", __progname); 257 if (valid_request(pw, host, &key, data, dlen) < 0) 258 fatal("%s: not a valid request", __progname); 259 free(host); 260 261 found = 0; 262 for (i = 0; i < NUM_KEYTYPES; i++) { 263 if (keys[i] != NULL && 264 sshkey_equal_public(key, keys[i])) { 265 found = 1; 266 break; 267 } 268 } 269 if (!found) { 270 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 271 SSH_FP_DEFAULT)) == NULL) 272 fatal("%s: sshkey_fingerprint failed", __progname); 273 fatal("%s: no matching hostkey found for key %s %s", __progname, 274 sshkey_type(key), fp ? fp : ""); 275 } 276 277 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 278 NULL, NULL, NULL, 0)) != 0) 279 fatal_r(r, "%s: sshkey_sign failed", __progname); 280 free(data); 281 282 /* send reply */ 283 sshbuf_reset(b); 284 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 285 fatal_r(r, "%s: buffer error", __progname); 286 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 287 fatal("%s: ssh_msg_send failed", __progname); 288 289 return (0); 290 } 291