crypto/openssh/ssh-keysign.c

   1 /* $OpenBSD: ssh-keysign.c,v 1.52 2016/02/15 09:47:49 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 <stdlib.h>
  35 #include <string.h>
  36 #include <unistd.h>
  37 #include <errno.h>
  38
  39 #ifdef WITH_OPENSSL
  40 #include <openssl/evp.h>
  41 #include <openssl/rand.h>
  42 #include <openssl/rsa.h>
  43 #endif
  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 "sshkey.h"
  59 #include "ssherr.h"
  60
  61 struct ssh *active_state = NULL; /* XXX needed for linking */
  62
  63 extern char *__progname;
  64
  65 /* XXX readconf.c needs these */
  66 uid_t original_real_uid;
  67
  68 extern char *__progname;
  69
  70 static int
  71 valid_request(struct passwd *pw, char *host, struct sshkey **ret,
  72     u_char *data, size_t datalen)
  73 {
  74         struct sshbuf *b;
  75         struct sshkey *key = NULL;
  76         u_char type, *pkblob;
  77         char *p;
  78         size_t blen, len;
  79         char *pkalg, *luser;
  80         int r, pktype, fail;
  81
  82         if (ret != NULL)
  83                 *ret = NULL;
  84         fail = 0;
  85
  86         if ((b = sshbuf_from(data, datalen)) == NULL)
  87                 fatal("%s: sshbuf_from failed", __func__);
  88
  89         /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
  90         if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
  91                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
  92         if (len != 20 && len != 32)
  93                 fail++;
  94
  95         if ((r = sshbuf_get_u8(b, &type)) != 0)
  96                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
  97         if (type != SSH2_MSG_USERAUTH_REQUEST)
  98                 fail++;
  99
 100         /* server user */
 101         if ((r = sshbuf_skip_string(b)) != 0)
 102                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 103
 104         /* service */
 105         if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
 106                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 107         if (strcmp("ssh-connection", p) != 0)
 108                 fail++;
 109         free(p);
 110
 111         /* method */
 112         if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
 113                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 114         if (strcmp("hostbased", p) != 0)
 115                 fail++;
 116         free(p);
 117
 118         /* pubkey */
 119         if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
 120             (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
 121                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 122
 123         pktype = sshkey_type_from_name(pkalg);
 124         if (pktype == KEY_UNSPEC)
 125                 fail++;
 126         else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
 127                 error("%s: bad key blob: %s", __func__, ssh_err(r));
 128                 fail++;
 129         } else if (key->type != pktype)
 130                 fail++;
 131         free(pkalg);
 132         free(pkblob);
 133
 134         /* client host name, handle trailing dot */
 135         if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
 136                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 137         debug2("%s: check expect chost %s got %s", __func__, host, p);
 138         if (strlen(host) != len - 1)
 139                 fail++;
 140         else if (p[len - 1] != '.')
 141                 fail++;
 142         else if (strncasecmp(host, p, len - 1) != 0)
 143                 fail++;
 144         free(p);
 145
 146         /* local user */
 147         if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
 148                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 149
 150         if (strcmp(pw->pw_name, luser) != 0)
 151                 fail++;
 152         free(luser);
 153
 154         /* end of message */
 155         if (sshbuf_len(b) != 0)
 156                 fail++;
 157         sshbuf_free(b);
 158
 159         debug3("%s: fail %d", __func__, fail);
 160
 161         if (fail && key != NULL)
 162                 sshkey_free(key);
 163         else if (ret != NULL)
 164                 *ret = key;
 165
 166         return (fail ? -1 : 0);
 167 }
 168
 169 int
 170 main(int argc, char **argv)
 171 {
 172         struct sshbuf *b;
 173         Options options;
 174 #define NUM_KEYTYPES 4
 175         struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
 176         struct passwd *pw;
 177         int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
 178         u_char *signature, *data, rver;
 179         char *host, *fp;
 180         size_t slen, dlen;
 181 #ifdef WITH_OPENSSL
 182         u_int32_t rnd[256];
 183 #endif
 184
 185         ssh_malloc_init();      /* must be called before any mallocs */
 186         if (pledge("stdio rpath getpw dns id", NULL) != 0)
 187                 fatal("%s: pledge: %s", __progname, strerror(errno));
 188
 189         /* Ensure that stdin and stdout are connected */
 190         if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
 191                 exit(1);
 192         /* Leave /dev/null fd iff it is attached to stderr */
 193         if (fd > 2)
 194                 close(fd);
 195
 196         i = 0;
 197         /* XXX This really needs to read sshd_config for the paths */
 198         key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
 199         key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
 200         key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
 201         key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
 202
 203         original_real_uid = getuid();   /* XXX readconf.c needs this */
 204         if ((pw = getpwuid(original_real_uid)) == NULL)
 205                 fatal("getpwuid failed");
 206         pw = pwcopy(pw);
 207
 208         permanently_set_uid(pw);
 209
 210         seed_rng();
 211
 212 #ifdef DEBUG_SSH_KEYSIGN
 213         log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
 214 #endif
 215
 216         /* verify that ssh-keysign is enabled by the admin */
 217         initialize_options(&options);
 218         (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0);
 219         fill_default_options(&options);
 220         if (options.enable_ssh_keysign != 1)
 221                 fatal("ssh-keysign not enabled in %s",
 222                     _PATH_HOST_CONFIG_FILE);
 223
 224         for (i = found = 0; i < NUM_KEYTYPES; i++) {
 225                 if (key_fd[i] != -1)
 226                         found = 1;
 227         }
 228         if (found == 0)
 229                 fatal("could not open any host key");
 230
 231 #ifdef WITH_OPENSSL
 232         OpenSSL_add_all_algorithms();
 233         arc4random_buf(rnd, sizeof(rnd));
 234         RAND_seed(rnd, sizeof(rnd));
 235 #endif
 236
 237         found = 0;
 238         for (i = 0; i < NUM_KEYTYPES; i++) {
 239                 keys[i] = NULL;
 240                 if (key_fd[i] == -1)
 241                         continue;
 242                 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
 243                     NULL, &key, NULL);
 244                 close(key_fd[i]);
 245                 if (r != 0)
 246                         debug("parse key %d: %s", i, ssh_err(r));
 247                 else if (key != NULL) {
 248                         keys[i] = key;
 249                         found = 1;
 250                 }
 251         }
 252         if (!found)
 253                 fatal("no hostkey found");
 254
 255         if (pledge("stdio dns", NULL) != 0)
 256                 fatal("%s: pledge: %s", __progname, strerror(errno));
 257
 258         if ((b = sshbuf_new()) == NULL)
 259                 fatal("%s: sshbuf_new failed", __progname);
 260         if (ssh_msg_recv(STDIN_FILENO, b) < 0)
 261                 fatal("ssh_msg_recv failed");
 262         if ((r = sshbuf_get_u8(b, &rver)) != 0)
 263                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
 264         if (rver != version)
 265                 fatal("bad version: received %d, expected %d", rver, version);
 266         if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
 267                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
 268         if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
 269                 fatal("bad fd");
 270         if ((host = get_local_name(fd)) == NULL)
 271                 fatal("cannot get local name for fd");
 272
 273         if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
 274                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
 275         if (valid_request(pw, host, &key, data, dlen) < 0)
 276                 fatal("not a valid request");
 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("no matching hostkey found for key %s %s",
 292                     sshkey_type(key), fp ? fp : "");
 293         }
 294
 295         if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0))
 296             != 0)
 297                 fatal("sshkey_sign failed: %s", ssh_err(r));
 298         free(data);
 299
 300         /* send reply */
 301         sshbuf_reset(b);
 302         if ((r = sshbuf_put_string(b, signature, slen)) != 0)
 303                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
 304         if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
 305                 fatal("ssh_msg_send failed");
 306
 307         return (0);
 308 }