ssh-keysign.c

   1 /* $OpenBSD: ssh-keysign.c,v 1.35 2010/08/31 12:33:38 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 <stdlib.h>
  35 #include <string.h>
  36 #include <unistd.h>
  37
  38 #include <openssl/evp.h>
  39 #include <openssl/rand.h>
  40 #include <openssl/rsa.h>
  41
  42 #include "xmalloc.h"
  43 #include "log.h"
  44 #include "key.h"
  45 #include "ssh.h"
  46 #include "ssh2.h"
  47 #include "misc.h"
  48 #include "buffer.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
  56 /* XXX readconf.c needs these */
  57 uid_t original_real_uid;
  58
  59 extern char *__progname;
  60
  61 static int
  62 valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
  63     u_int datalen)
  64 {
  65         Buffer b;
  66         Key *key = NULL;
  67         u_char *pkblob;
  68         u_int blen, len;
  69         char *pkalg, *p;
  70         int pktype, fail;
  71
  72         fail = 0;
  73
  74         buffer_init(&b);
  75         buffer_append(&b, data, datalen);
  76
  77         /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
  78         p = buffer_get_string(&b, &len);
  79         if (len != 20 && len != 32)
  80                 fail++;
  81         xfree(p);
  82
  83         if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
  84                 fail++;
  85
  86         /* server user */
  87         buffer_skip_string(&b);
  88
  89         /* service */
  90         p = buffer_get_string(&b, NULL);
  91         if (strcmp("ssh-connection", p) != 0)
  92                 fail++;
  93         xfree(p);
  94
  95         /* method */
  96         p = buffer_get_string(&b, NULL);
  97         if (strcmp("hostbased", p) != 0)
  98                 fail++;
  99         xfree(p);
 100
 101         /* pubkey */
 102         pkalg = buffer_get_string(&b, NULL);
 103         pkblob = buffer_get_string(&b, &blen);
 104
 105         pktype = key_type_from_name(pkalg);
 106         if (pktype == KEY_UNSPEC)
 107                 fail++;
 108         else if ((key = key_from_blob(pkblob, blen)) == NULL)
 109                 fail++;
 110         else if (key->type != pktype)
 111                 fail++;
 112         xfree(pkalg);
 113         xfree(pkblob);
 114
 115         /* client host name, handle trailing dot */
 116         p = buffer_get_string(&b, &len);
 117         debug2("valid_request: check expect chost %s got %s", host, p);
 118         if (strlen(host) != len - 1)
 119                 fail++;
 120         else if (p[len - 1] != '.')
 121                 fail++;
 122         else if (strncasecmp(host, p, len - 1) != 0)
 123                 fail++;
 124         xfree(p);
 125
 126         /* local user */
 127         p = buffer_get_string(&b, NULL);
 128
 129         if (strcmp(pw->pw_name, p) != 0)
 130                 fail++;
 131         xfree(p);
 132
 133         /* end of message */
 134         if (buffer_len(&b) != 0)
 135                 fail++;
 136         buffer_free(&b);
 137
 138         debug3("valid_request: fail %d", fail);
 139
 140         if (fail && key != NULL)
 141                 key_free(key);
 142         else
 143                 *ret = key;
 144
 145         return (fail ? -1 : 0);
 146 }
 147
 148 int
 149 main(int argc, char **argv)
 150 {
 151         Buffer b;
 152         Options options;
 153         Key *keys[2], *key = NULL;
 154         struct passwd *pw;
 155         int key_fd[2], i, found, version = 2, fd;
 156         u_char *signature, *data;
 157         char *host;
 158         u_int slen, dlen;
 159         u_int32_t rnd[256];
 160
 161         /* Ensure that stdin and stdout are connected */
 162         if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
 163                 exit(1);
 164         /* Leave /dev/null fd iff it is attached to stderr */
 165         if (fd > 2)
 166                 close(fd);
 167
 168         key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
 169         key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
 170
 171         original_real_uid = getuid();   /* XXX readconf.c needs this */
 172         if ((pw = getpwuid(original_real_uid)) == NULL)
 173                 fatal("getpwuid failed");
 174         pw = pwcopy(pw);
 175
 176         permanently_set_uid(pw);
 177
 178         init_rng();
 179         seed_rng();
 180         arc4random_stir();
 181
 182 #ifdef DEBUG_SSH_KEYSIGN
 183         log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
 184 #endif
 185
 186         /* verify that ssh-keysign is enabled by the admin */
 187         initialize_options(&options);
 188         (void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0);
 189         fill_default_options(&options);
 190         if (options.enable_ssh_keysign != 1)
 191                 fatal("ssh-keysign not enabled in %s",
 192                     _PATH_HOST_CONFIG_FILE);
 193
 194         if (key_fd[0] == -1 && key_fd[1] == -1)
 195                 fatal("could not open any host key");
 196
 197         OpenSSL_add_all_algorithms();
 198         for (i = 0; i < 256; i++)
 199                 rnd[i] = arc4random();
 200         RAND_seed(rnd, sizeof(rnd));
 201
 202         found = 0;
 203         for (i = 0; i < 2; i++) {
 204                 keys[i] = NULL;
 205                 if (key_fd[i] == -1)
 206                         continue;
 207                 keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
 208                     NULL, NULL);
 209                 close(key_fd[i]);
 210                 if (keys[i] != NULL)
 211                         found = 1;
 212         }
 213         if (!found)
 214                 fatal("no hostkey found");
 215
 216         buffer_init(&b);
 217         if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
 218                 fatal("ssh_msg_recv failed");
 219         if (buffer_get_char(&b) != version)
 220                 fatal("bad version");
 221         fd = buffer_get_int(&b);
 222         if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
 223                 fatal("bad fd");
 224         if ((host = get_local_name(fd)) == NULL)
 225                 fatal("cannot get local name for fd");
 226
 227         data = buffer_get_string(&b, &dlen);
 228         if (valid_request(pw, host, &key, data, dlen) < 0)
 229                 fatal("not a valid request");
 230         xfree(host);
 231
 232         found = 0;
 233         for (i = 0; i < 2; i++) {
 234                 if (keys[i] != NULL &&
 235                     key_equal_public(key, keys[i])) {
 236                         found = 1;
 237                         break;
 238                 }
 239         }
 240         if (!found)
 241                 fatal("no matching hostkey found");
 242
 243         if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
 244                 fatal("key_sign failed");
 245         xfree(data);
 246
 247         /* send reply */
 248         buffer_clear(&b);
 249         buffer_put_string(&b, signature, slen);
 250         if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
 251                 fatal("ssh_msg_send failed");
 252
 253         return (0);
 254 }