crypto/openssh/ssh-keysign.c

   1 /* $OpenBSD: ssh-keysign.c,v 1.71 2022/08/01 11:09:26 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 <stdio.h>
  35 #include <stdlib.h>
  36 #include <string.h>
  37 #include <unistd.h>
  38 #include <errno.h>
  39
  40 #ifdef WITH_OPENSSL
  41 #include <openssl/evp.h>
  42 #include <openssl/rand.h>
  43 #include <openssl/rsa.h>
  44 #include "openbsd-compat/openssl-compat.h"
  45 #endif
  46
  47 #include "xmalloc.h"
  48 #include "log.h"
  49 #include "sshkey.h"
  50 #include "ssh.h"
  51 #include "ssh2.h"
  52 #include "misc.h"
  53 #include "sshbuf.h"
  54 #include "authfile.h"
  55 #include "msg.h"
  56 #include "canohost.h"
  57 #include "pathnames.h"
  58 #include "readconf.h"
  59 #include "uidswap.h"
  60 #include "ssherr.h"
  61
  62 extern char *__progname;
  63
  64 static int
  65 valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
  66     u_char *data, size_t datalen)
  67 {
  68         struct sshbuf *b;
  69         struct sshkey *key = NULL;
  70         u_char type, *pkblob;
  71         char *p;
  72         size_t blen, len;
  73         char *pkalg, *luser;
  74         int r, pktype, fail;
  75
  76         if (ret != NULL)
  77                 *ret = NULL;
  78         if (pkalgp != NULL)
  79                 *pkalgp = NULL;
  80         fail = 0;
  81
  82         if ((b = sshbuf_from(data, datalen)) == NULL)
  83                 fatal_f("sshbuf_from failed");
  84
  85         /* session id */
  86         if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
  87                 fatal_fr(r, "parse session ID");
  88         if (len != 20 && /* SHA1 */
  89             len != 32 && /* SHA256 */
  90             len != 48 && /* SHA384 */
  91             len != 64)   /* SHA512 */
  92                 fail++;
  93
  94         if ((r = sshbuf_get_u8(b, &type)) != 0)
  95                 fatal_fr(r, "parse type");
  96         if (type != SSH2_MSG_USERAUTH_REQUEST)
  97                 fail++;
  98
  99         /* server user */
 100         if ((r = sshbuf_skip_string(b)) != 0)
 101                 fatal_fr(r, "parse user");
 102
 103         /* service */
 104         if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
 105                 fatal_fr(r, "parse service");
 106         if (strcmp("ssh-connection", p) != 0)
 107                 fail++;
 108         free(p);
 109
 110         /* method */
 111         if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
 112                 fatal_fr(r, "parse method");
 113         if (strcmp("hostbased", p) != 0)
 114                 fail++;
 115         free(p);
 116
 117         /* pubkey */
 118         if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
 119             (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
 120                 fatal_fr(r, "parse pk");
 121
 122         pktype = sshkey_type_from_name(pkalg);
 123         if (pktype == KEY_UNSPEC)
 124                 fail++;
 125         else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
 126                 error_fr(r, "decode key");
 127                 fail++;
 128         } else if (key->type != pktype)
 129                 fail++;
 130
 131         /* client host name, handle trailing dot */
 132         if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
 133                 fatal_fr(r, "parse hostname");
 134         debug2_f("check expect chost %s got %s", host, p);
 135         if (strlen(host) != len - 1)
 136                 fail++;
 137         else if (p[len - 1] != '.')
 138                 fail++;
 139         else if (strncasecmp(host, p, len - 1) != 0)
 140                 fail++;
 141         free(p);
 142
 143         /* local user */
 144         if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
 145                 fatal_fr(r, "parse luser");
 146
 147         if (strcmp(pw->pw_name, luser) != 0)
 148                 fail++;
 149         free(luser);
 150
 151         /* end of message */
 152         if (sshbuf_len(b) != 0)
 153                 fail++;
 154         sshbuf_free(b);
 155
 156         debug3_f("fail %d", fail);
 157
 158         if (!fail) {
 159                 if (ret != NULL) {
 160                         *ret = key;
 161                         key = NULL;
 162                 }
 163                 if (pkalgp != NULL) {
 164                         *pkalgp = pkalg;
 165                         pkalg = NULL;
 166                 }
 167         }
 168         sshkey_free(key);
 169         free(pkalg);
 170         free(pkblob);
 171
 172         return (fail ? -1 : 0);
 173 }
 174
 175 int
 176 main(int argc, char **argv)
 177 {
 178         struct sshbuf *b;
 179         Options options;
 180 #define NUM_KEYTYPES 5
 181         struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
 182         struct passwd *pw;
 183         int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
 184         u_char *signature, *data, rver;
 185         char *host, *fp, *pkalg;
 186         size_t slen, dlen;
 187
 188         if (pledge("stdio rpath getpw dns id", NULL) != 0)
 189                 fatal("%s: pledge: %s", __progname, strerror(errno));
 190
 191         /* Ensure that stdin and stdout are connected */
 192         if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
 193                 exit(1);
 194         /* Leave /dev/null fd iff it is attached to stderr */
 195         if (fd > 2)
 196                 close(fd);
 197
 198         i = 0;
 199         /* XXX This really needs to read sshd_config for the paths */
 200         key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
 201         key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
 202         key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
 203         key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
 204         key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
 205
 206         if ((pw = getpwuid(getuid())) == NULL)
 207                 fatal("getpwuid failed");
 208         pw = pwcopy(pw);
 209
 210         permanently_set_uid(pw);
 211
 212         seed_rng();
 213
 214 #ifdef DEBUG_SSH_KEYSIGN
 215         log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
 216 #endif
 217
 218         /* verify that ssh-keysign is enabled by the admin */
 219         initialize_options(&options);
 220         (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "",
 221             &options, 0, NULL);
 222         (void)fill_default_options(&options);
 223         if (options.enable_ssh_keysign != 1)
 224                 fatal("ssh-keysign not enabled in %s",
 225                     _PATH_HOST_CONFIG_FILE);
 226
 227         if (pledge("stdio dns", NULL) != 0)
 228                 fatal("%s: pledge: %s", __progname, strerror(errno));
 229
 230         for (i = found = 0; i < NUM_KEYTYPES; i++) {
 231                 if (key_fd[i] != -1)
 232                         found = 1;
 233         }
 234         if (found == 0)
 235                 fatal("could not open any host key");
 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_r(r, "parse key %d", i);
 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 ((b = sshbuf_new()) == NULL)
 256                 fatal("%s: sshbuf_new failed", __progname);
 257         if (ssh_msg_recv(STDIN_FILENO, b) < 0)
 258                 fatal("%s: ssh_msg_recv failed", __progname);
 259         if ((r = sshbuf_get_u8(b, &rver)) != 0)
 260                 fatal_r(r, "%s: buffer error", __progname);
 261         if (rver != version)
 262                 fatal("%s: bad version: received %d, expected %d",
 263                     __progname, rver, version);
 264         if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
 265                 fatal_r(r, "%s: buffer error", __progname);
 266         if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
 267                 fatal("%s: bad fd = %d", __progname, fd);
 268         if ((host = get_local_name(fd)) == NULL)
 269                 fatal("%s: cannot get local name for fd", __progname);
 270
 271         if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
 272                 fatal_r(r, "%s: buffer error", __progname);
 273         if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
 274                 fatal("%s: not a valid request", __progname);
 275         free(host);
 276
 277         found = 0;
 278         for (i = 0; i < NUM_KEYTYPES; i++) {
 279                 if (keys[i] != NULL &&
 280                     sshkey_equal_public(key, keys[i])) {
 281                         found = 1;
 282                         break;
 283                 }
 284         }
 285         if (!found) {
 286                 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
 287                     SSH_FP_DEFAULT)) == NULL)
 288                         fatal("%s: sshkey_fingerprint failed", __progname);
 289                 fatal("%s: no matching hostkey found for key %s %s", __progname,
 290                     sshkey_type(key), fp ? fp : "");
 291         }
 292
 293         if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
 294             pkalg, NULL, NULL, 0)) != 0)
 295                 fatal_r(r, "%s: sshkey_sign failed", __progname);
 296         free(data);
 297
 298         /* send reply */
 299         sshbuf_reset(b);
 300         if ((r = sshbuf_put_string(b, signature, slen)) != 0)
 301                 fatal_r(r, "%s: buffer error", __progname);
 302         if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
 303                 fatal("%s: ssh_msg_send failed", __progname);
 304
 305         return (0);
 306 }