ssh-keysign.c

   1 /* $OpenBSD: ssh-keysign.c,v 1.29 2006/08/03 03:34:42 deraadt 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 <stdlib.h>
  34 #include <string.h>
  35 #include <unistd.h>
  36
  37 #include <openssl/evp.h>
  38 #include <openssl/rand.h>
  39 #include <openssl/rsa.h>
  40
  41 #include "xmalloc.h"
  42 #include "log.h"
  43 #include "key.h"
  44 #include "ssh.h"
  45 #include "ssh2.h"
  46 #include "misc.h"
  47 #include "buffer.h"
  48 #include "authfile.h"
  49 #include "msg.h"
  50 #include "canohost.h"
  51 #include "pathnames.h"
  52 #include "readconf.h"
  53 #include "uidswap.h"
  54
  55 /* XXX readconf.c needs these */
  56 uid_t original_real_uid;
  57
  58 extern char *__progname;
  59
  60 static int
  61 valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
  62     u_int datalen)
  63 {
  64         Buffer b;
  65         Key *key = NULL;
  66         u_char *pkblob;
  67         u_int blen, len;
  68         char *pkalg, *p;
  69         int pktype, fail;
  70
  71         fail = 0;
  72
  73         buffer_init(&b);
  74         buffer_append(&b, data, datalen);
  75
  76         /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
  77         p = buffer_get_string(&b, &len);
  78         if (len != 20 && len != 32)
  79                 fail++;
  80         xfree(p);
  81
  82         if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
  83                 fail++;
  84
  85         /* server user */
  86         buffer_skip_string(&b);
  87
  88         /* service */
  89         p = buffer_get_string(&b, NULL);
  90         if (strcmp("ssh-connection", p) != 0)
  91                 fail++;
  92         xfree(p);
  93
  94         /* method */
  95         p = buffer_get_string(&b, NULL);
  96         if (strcmp("hostbased", p) != 0)
  97                 fail++;
  98         xfree(p);
  99
 100         /* pubkey */
 101         pkalg = buffer_get_string(&b, NULL);
 102         pkblob = buffer_get_string(&b, &blen);
 103
 104         pktype = key_type_from_name(pkalg);
 105         if (pktype == KEY_UNSPEC)
 106                 fail++;
 107         else if ((key = key_from_blob(pkblob, blen)) == NULL)
 108                 fail++;
 109         else if (key->type != pktype)
 110                 fail++;
 111         xfree(pkalg);
 112         xfree(pkblob);
 113
 114         /* client host name, handle trailing dot */
 115         p = buffer_get_string(&b, &len);
 116         debug2("valid_request: check expect chost %s got %s", host, p);
 117         if (strlen(host) != len - 1)
 118                 fail++;
 119         else if (p[len - 1] != '.')
 120                 fail++;
 121         else if (strncasecmp(host, p, len - 1) != 0)
 122                 fail++;
 123         xfree(p);
 124
 125         /* local user */
 126         p = buffer_get_string(&b, NULL);
 127
 128         if (strcmp(pw->pw_name, p) != 0)
 129                 fail++;
 130         xfree(p);
 131
 132         /* end of message */
 133         if (buffer_len(&b) != 0)
 134                 fail++;
 135         buffer_free(&b);
 136
 137         debug3("valid_request: fail %d", fail);
 138
 139         if (fail && key != NULL)
 140                 key_free(key);
 141         else
 142                 *ret = key;
 143
 144         return (fail ? -1 : 0);
 145 }
 146
 147 int
 148 main(int argc, char **argv)
 149 {
 150         Buffer b;
 151         Options options;
 152         Key *keys[2], *key = NULL;
 153         struct passwd *pw;
 154         int key_fd[2], i, found, version = 2, fd;
 155         u_char *signature, *data;
 156         char *host;
 157         u_int slen, dlen;
 158         u_int32_t rnd[256];
 159
 160         /* Ensure that stdin and stdout are connected */
 161         if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
 162                 exit(1);
 163         /* Leave /dev/null fd iff it is attached to stderr */
 164         if (fd > 2)
 165                 close(fd);
 166
 167         key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
 168         key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
 169
 170         original_real_uid = getuid();   /* XXX readconf.c needs this */
 171         if ((pw = getpwuid(original_real_uid)) == NULL)
 172                 fatal("getpwuid failed");
 173         pw = pwcopy(pw);
 174
 175         permanently_set_uid(pw);
 176
 177         init_rng();
 178         seed_rng();
 179         arc4random_stir();
 180
 181 #ifdef DEBUG_SSH_KEYSIGN
 182         log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
 183 #endif
 184
 185         /* verify that ssh-keysign is enabled by the admin */
 186         initialize_options(&options);
 187         (void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0);
 188         fill_default_options(&options);
 189         if (options.enable_ssh_keysign != 1)
 190                 fatal("ssh-keysign not enabled in %s",
 191                     _PATH_HOST_CONFIG_FILE);
 192
 193         if (key_fd[0] == -1 && key_fd[1] == -1)
 194                 fatal("could not open any host key");
 195
 196         SSLeay_add_all_algorithms();
 197         for (i = 0; i < 256; i++)
 198                 rnd[i] = arc4random();
 199         RAND_seed(rnd, sizeof(rnd));
 200
 201         found = 0;
 202         for (i = 0; i < 2; i++) {
 203                 keys[i] = NULL;
 204                 if (key_fd[i] == -1)
 205                         continue;
 206                 keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
 207                     NULL, NULL);
 208                 close(key_fd[i]);
 209                 if (keys[i] != NULL)
 210                         found = 1;
 211         }
 212         if (!found)
 213                 fatal("no hostkey found");
 214
 215         buffer_init(&b);
 216         if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
 217                 fatal("ssh_msg_recv failed");
 218         if (buffer_get_char(&b) != version)
 219                 fatal("bad version");
 220         fd = buffer_get_int(&b);
 221         if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
 222                 fatal("bad fd");
 223         if ((host = get_local_name(fd)) == NULL)
 224                 fatal("cannot get sockname for fd");
 225
 226         data = buffer_get_string(&b, &dlen);
 227         if (valid_request(pw, host, &key, data, dlen) < 0)
 228                 fatal("not a valid request");
 229         xfree(host);
 230
 231         found = 0;
 232         for (i = 0; i < 2; i++) {
 233                 if (keys[i] != NULL &&
 234                     key_equal(key, keys[i])) {
 235                         found = 1;
 236                         break;
 237                 }
 238         }
 239         if (!found)
 240                 fatal("no matching hostkey found");
 241
 242         if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
 243                 fatal("key_sign failed");
 244         xfree(data);
 245
 246         /* send reply */
 247         buffer_clear(&b);
 248         buffer_put_string(&b, signature, slen);
 249         if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
 250                 fatal("ssh_msg_send failed");
 251
 252         return (0);
 253 }