ssh-keysign.c

   1 /* $OpenBSD: ssh-keysign.c,v 1.27 2006/07/22 20:48:23 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 <string.h>
  33 #include <unistd.h>
  34
  35 #include <openssl/evp.h>
  36 #include <openssl/rand.h>
  37 #include <openssl/rsa.h>
  38
  39 #include "log.h"
  40 #include "key.h"
  41 #include "ssh.h"
  42 #include "ssh2.h"
  43 #include "misc.h"
  44 #include "xmalloc.h"
  45 #include "buffer.h"
  46 #include "bufaux.h"
  47 #include "authfile.h"
  48 #include "msg.h"
  49 #include "canohost.h"
  50 #include "pathnames.h"
  51 #include "readconf.h"
  52 #include "uidswap.h"
  53
  54 /* XXX readconf.c needs these */
  55 uid_t original_real_uid;
  56
  57 extern char *__progname;
  58
  59 static int
  60 valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
  61     u_int datalen)
  62 {
  63         Buffer b;
  64         Key *key = NULL;
  65         u_char *pkblob;
  66         u_int blen, len;
  67         char *pkalg, *p;
  68         int pktype, fail;
  69
  70         fail = 0;
  71
  72         buffer_init(&b);
  73         buffer_append(&b, data, datalen);
  74
  75         /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
  76         p = buffer_get_string(&b, &len);
  77         if (len != 20 && len != 32)
  78                 fail++;
  79         xfree(p);
  80
  81         if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
  82                 fail++;
  83
  84         /* server user */
  85         buffer_skip_string(&b);
  86
  87         /* service */
  88         p = buffer_get_string(&b, NULL);
  89         if (strcmp("ssh-connection", p) != 0)
  90                 fail++;
  91         xfree(p);
  92
  93         /* method */
  94         p = buffer_get_string(&b, NULL);
  95         if (strcmp("hostbased", p) != 0)
  96                 fail++;
  97         xfree(p);
  98
  99         /* pubkey */
 100         pkalg = buffer_get_string(&b, NULL);
 101         pkblob = buffer_get_string(&b, &blen);
 102
 103         pktype = key_type_from_name(pkalg);
 104         if (pktype == KEY_UNSPEC)
 105                 fail++;
 106         else if ((key = key_from_blob(pkblob, blen)) == NULL)
 107                 fail++;
 108         else if (key->type != pktype)
 109                 fail++;
 110         xfree(pkalg);
 111         xfree(pkblob);
 112
 113         /* client host name, handle trailing dot */
 114         p = buffer_get_string(&b, &len);
 115         debug2("valid_request: check expect chost %s got %s", host, p);
 116         if (strlen(host) != len - 1)
 117                 fail++;
 118         else if (p[len - 1] != '.')
 119                 fail++;
 120         else if (strncasecmp(host, p, len - 1) != 0)
 121                 fail++;
 122         xfree(p);
 123
 124         /* local user */
 125         p = buffer_get_string(&b, NULL);
 126
 127         if (strcmp(pw->pw_name, p) != 0)
 128                 fail++;
 129         xfree(p);
 130
 131         /* end of message */
 132         if (buffer_len(&b) != 0)
 133                 fail++;
 134         buffer_free(&b);
 135
 136         debug3("valid_request: fail %d", fail);
 137
 138         if (fail && key != NULL)
 139                 key_free(key);
 140         else
 141                 *ret = key;
 142
 143         return (fail ? -1 : 0);
 144 }
 145
 146 int
 147 main(int argc, char **argv)
 148 {
 149         Buffer b;
 150         Options options;
 151         Key *keys[2], *key = NULL;
 152         struct passwd *pw;
 153         int key_fd[2], i, found, version = 2, fd;
 154         u_char *signature, *data;
 155         char *host;
 156         u_int slen, dlen;
 157         u_int32_t rnd[256];
 158
 159         /* Ensure that stdin and stdout are connected */
 160         if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
 161                 exit(1);
 162         /* Leave /dev/null fd iff it is attached to stderr */
 163         if (fd > 2)
 164                 close(fd);
 165
 166         key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
 167         key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
 168
 169         original_real_uid = getuid();   /* XXX readconf.c needs this */
 170         if ((pw = getpwuid(original_real_uid)) == NULL)
 171                 fatal("getpwuid failed");
 172         pw = pwcopy(pw);
 173
 174         permanently_set_uid(pw);
 175
 176         init_rng();
 177         seed_rng();
 178         arc4random_stir();
 179
 180 #ifdef DEBUG_SSH_KEYSIGN
 181         log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
 182 #endif
 183
 184         /* verify that ssh-keysign is enabled by the admin */
 185         initialize_options(&options);
 186         (void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0);
 187         fill_default_options(&options);
 188         if (options.enable_ssh_keysign != 1)
 189                 fatal("ssh-keysign not enabled in %s",
 190                     _PATH_HOST_CONFIG_FILE);
 191
 192         if (key_fd[0] == -1 && key_fd[1] == -1)
 193                 fatal("could not open any host key");
 194
 195         SSLeay_add_all_algorithms();
 196         for (i = 0; i < 256; i++)
 197                 rnd[i] = arc4random();
 198         RAND_seed(rnd, sizeof(rnd));
 199
 200         found = 0;
 201         for (i = 0; i < 2; i++) {
 202                 keys[i] = NULL;
 203                 if (key_fd[i] == -1)
 204                         continue;
 205                 keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
 206                     NULL, NULL);
 207                 close(key_fd[i]);
 208                 if (keys[i] != NULL)
 209                         found = 1;
 210         }
 211         if (!found)
 212                 fatal("no hostkey found");
 213
 214         buffer_init(&b);
 215         if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
 216                 fatal("ssh_msg_recv failed");
 217         if (buffer_get_char(&b) != version)
 218                 fatal("bad version");
 219         fd = buffer_get_int(&b);
 220         if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
 221                 fatal("bad fd");
 222         if ((host = get_local_name(fd)) == NULL)
 223                 fatal("cannot get sockname for fd");
 224
 225         data = buffer_get_string(&b, &dlen);
 226         if (valid_request(pw, host, &key, data, dlen) < 0)
 227                 fatal("not a valid request");
 228         xfree(host);
 229
 230         found = 0;
 231         for (i = 0; i < 2; i++) {
 232                 if (keys[i] != NULL &&
 233                     key_equal(key, keys[i])) {
 234                         found = 1;
 235                         break;
 236                 }
 237         }
 238         if (!found)
 239                 fatal("no matching hostkey found");
 240
 241         if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
 242                 fatal("key_sign failed");
 243         xfree(data);
 244
 245         /* send reply */
 246         buffer_clear(&b);
 247         buffer_put_string(&b, signature, slen);
 248         if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
 249                 fatal("ssh_msg_send failed");
 250
 251         return (0);
 252 }