ssh-keysign.c

   1 /* $OpenBSD: ssh-keysign.c,v 1.26 2006/07/17 01:31:10 stevesk 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 #include "includes.h"
  26
  27 #include <fcntl.h>
  28 #ifdef HAVE_PATHS_H
  29 #include <paths.h>
  30 #endif
  31 #include <pwd.h>
  32 #include <unistd.h>
  33
  34 #include <openssl/evp.h>
  35 #include <openssl/rand.h>
  36 #include <openssl/rsa.h>
  37
  38 #include "log.h"
  39 #include "key.h"
  40 #include "ssh.h"
  41 #include "ssh2.h"
  42 #include "misc.h"
  43 #include "xmalloc.h"
  44 #include "buffer.h"
  45 #include "bufaux.h"
  46 #include "authfile.h"
  47 #include "msg.h"
  48 #include "canohost.h"
  49 #include "pathnames.h"
  50 #include "readconf.h"
  51 #include "uidswap.h"
  52
  53 /* XXX readconf.c needs these */
  54 uid_t original_real_uid;
  55
  56 extern char *__progname;
  57
  58 static int
  59 valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
  60     u_int datalen)
  61 {
  62         Buffer b;
  63         Key *key = NULL;
  64         u_char *pkblob;
  65         u_int blen, len;
  66         char *pkalg, *p;
  67         int pktype, fail;
  68
  69         fail = 0;
  70
  71         buffer_init(&b);
  72         buffer_append(&b, data, datalen);
  73
  74         /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
  75         p = buffer_get_string(&b, &len);
  76         if (len != 20 && len != 32)
  77                 fail++;
  78         xfree(p);
  79
  80         if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
  81                 fail++;
  82
  83         /* server user */
  84         buffer_skip_string(&b);
  85
  86         /* service */
  87         p = buffer_get_string(&b, NULL);
  88         if (strcmp("ssh-connection", p) != 0)
  89                 fail++;
  90         xfree(p);
  91
  92         /* method */
  93         p = buffer_get_string(&b, NULL);
  94         if (strcmp("hostbased", p) != 0)
  95                 fail++;
  96         xfree(p);
  97
  98         /* pubkey */
  99         pkalg = buffer_get_string(&b, NULL);
 100         pkblob = buffer_get_string(&b, &blen);
 101
 102         pktype = key_type_from_name(pkalg);
 103         if (pktype == KEY_UNSPEC)
 104                 fail++;
 105         else if ((key = key_from_blob(pkblob, blen)) == NULL)
 106                 fail++;
 107         else if (key->type != pktype)
 108                 fail++;
 109         xfree(pkalg);
 110         xfree(pkblob);
 111
 112         /* client host name, handle trailing dot */
 113         p = buffer_get_string(&b, &len);
 114         debug2("valid_request: check expect chost %s got %s", host, p);
 115         if (strlen(host) != len - 1)
 116                 fail++;
 117         else if (p[len - 1] != '.')
 118                 fail++;
 119         else if (strncasecmp(host, p, len - 1) != 0)
 120                 fail++;
 121         xfree(p);
 122
 123         /* local user */
 124         p = buffer_get_string(&b, NULL);
 125
 126         if (strcmp(pw->pw_name, p) != 0)
 127                 fail++;
 128         xfree(p);
 129
 130         /* end of message */
 131         if (buffer_len(&b) != 0)
 132                 fail++;
 133         buffer_free(&b);
 134
 135         debug3("valid_request: fail %d", fail);
 136
 137         if (fail && key != NULL)
 138                 key_free(key);
 139         else
 140                 *ret = key;
 141
 142         return (fail ? -1 : 0);
 143 }
 144
 145 int
 146 main(int argc, char **argv)
 147 {
 148         Buffer b;
 149         Options options;
 150         Key *keys[2], *key;
 151         struct passwd *pw;
 152         int key_fd[2], i, found, version = 2, fd;
 153         u_char *signature, *data;
 154         char *host;
 155         u_int slen, dlen;
 156         u_int32_t rnd[256];
 157
 158         /* Ensure that stdin and stdout are connected */
 159         if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
 160                 exit(1);
 161         /* Leave /dev/null fd iff it is attached to stderr */
 162         if (fd > 2)
 163                 close(fd);
 164
 165         key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
 166         key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
 167
 168         original_real_uid = getuid();   /* XXX readconf.c needs this */
 169         if ((pw = getpwuid(original_real_uid)) == NULL)
 170                 fatal("getpwuid failed");
 171         pw = pwcopy(pw);
 172
 173         permanently_set_uid(pw);
 174
 175         init_rng();
 176         seed_rng();
 177         arc4random_stir();
 178
 179 #ifdef DEBUG_SSH_KEYSIGN
 180         log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
 181 #endif
 182
 183         /* verify that ssh-keysign is enabled by the admin */
 184         initialize_options(&options);
 185         (void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0);
 186         fill_default_options(&options);
 187         if (options.enable_ssh_keysign != 1)
 188                 fatal("ssh-keysign not enabled in %s",
 189                     _PATH_HOST_CONFIG_FILE);
 190
 191         if (key_fd[0] == -1 && key_fd[1] == -1)
 192                 fatal("could not open any host key");
 193
 194         SSLeay_add_all_algorithms();
 195         for (i = 0; i < 256; i++)
 196                 rnd[i] = arc4random();
 197         RAND_seed(rnd, sizeof(rnd));
 198
 199         found = 0;
 200         for (i = 0; i < 2; i++) {
 201                 keys[i] = NULL;
 202                 if (key_fd[i] == -1)
 203                         continue;
 204                 keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
 205                     NULL, NULL);
 206                 close(key_fd[i]);
 207                 if (keys[i] != NULL)
 208                         found = 1;
 209         }
 210         if (!found)
 211                 fatal("no hostkey found");
 212
 213         buffer_init(&b);
 214         if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
 215                 fatal("ssh_msg_recv failed");
 216         if (buffer_get_char(&b) != version)
 217                 fatal("bad version");
 218         fd = buffer_get_int(&b);
 219         if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
 220                 fatal("bad fd");
 221         if ((host = get_local_name(fd)) == NULL)
 222                 fatal("cannot get sockname for fd");
 223
 224         data = buffer_get_string(&b, &dlen);
 225         if (valid_request(pw, host, &key, data, dlen) < 0)
 226                 fatal("not a valid request");
 227         xfree(host);
 228
 229         found = 0;
 230         for (i = 0; i < 2; i++) {
 231                 if (keys[i] != NULL &&
 232                     key_equal(key, keys[i])) {
 233                         found = 1;
 234                         break;
 235                 }
 236         }
 237         if (!found)
 238                 fatal("no matching hostkey found");
 239
 240         if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
 241                 fatal("key_sign failed");
 242         xfree(data);
 243
 244         /* send reply */
 245         buffer_clear(&b);
 246         buffer_put_string(&b, signature, slen);
 247         if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
 248                 fatal("ssh_msg_send failed");
 249
 250         return (0);
 251 }