auth2-pubkey.c

   1 /*
   2  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26 RCSID("$OpenBSD: auth2-pubkey.c,v 1.9 2004/12/11 01:48:56 dtucker Exp $");
  27
  28 #include "ssh.h"
  29 #include "ssh2.h"
  30 #include "xmalloc.h"
  31 #include "packet.h"
  32 #include "buffer.h"
  33 #include "log.h"
  34 #include "servconf.h"
  35 #include "compat.h"
  36 #include "bufaux.h"
  37 #include "auth.h"
  38 #include "key.h"
  39 #include "pathnames.h"
  40 #include "uidswap.h"
  41 #include "auth-options.h"
  42 #include "canohost.h"
  43 #include "monitor_wrap.h"
  44 #include "misc.h"
  45
  46 /* import */
  47 extern ServerOptions options;
  48 extern u_char *session_id2;
  49 extern u_int session_id2_len;
  50
  51 static int
  52 userauth_pubkey(Authctxt *authctxt)
  53 {
  54         Buffer b;
  55         Key *key = NULL;
  56         char *pkalg;
  57         u_char *pkblob, *sig;
  58         u_int alen, blen, slen;
  59         int have_sig, pktype;
  60         int authenticated = 0;
  61
  62         if (!authctxt->valid) {
  63                 debug2("userauth_pubkey: disabled because of invalid user");
  64                 return 0;
  65         }
  66         have_sig = packet_get_char();
  67         if (datafellows & SSH_BUG_PKAUTH) {
  68                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  69                 /* no explicit pkalg given */
  70                 pkblob = packet_get_string(&blen);
  71                 buffer_init(&b);
  72                 buffer_append(&b, pkblob, blen);
  73                 /* so we have to extract the pkalg from the pkblob */
  74                 pkalg = buffer_get_string(&b, &alen);
  75                 buffer_free(&b);
  76         } else {
  77                 pkalg = packet_get_string(&alen);
  78                 pkblob = packet_get_string(&blen);
  79         }
  80         pktype = key_type_from_name(pkalg);
  81         if (pktype == KEY_UNSPEC) {
  82                 /* this is perfectly legal */
  83                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  84                     pkalg);
  85                 goto done;
  86         }
  87         key = key_from_blob(pkblob, blen);
  88         if (key == NULL) {
  89                 error("userauth_pubkey: cannot decode key: %s", pkalg);
  90                 goto done;
  91         }
  92         if (key->type != pktype) {
  93                 error("userauth_pubkey: type mismatch for decoded key "
  94                     "(received %d, expected %d)", key->type, pktype);
  95                 goto done;
  96         }
  97         if (have_sig) {
  98                 sig = packet_get_string(&slen);
  99                 packet_check_eom();
 100                 buffer_init(&b);
 101                 if (datafellows & SSH_OLD_SESSIONID) {
 102                         buffer_append(&b, session_id2, session_id2_len);
 103                 } else {
 104                         buffer_put_string(&b, session_id2, session_id2_len);
 105                 }
 106                 /* reconstruct packet */
 107                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 108                 buffer_put_cstring(&b, authctxt->user);
 109                 buffer_put_cstring(&b,
 110                     datafellows & SSH_BUG_PKSERVICE ?
 111                     "ssh-userauth" :
 112                     authctxt->service);
 113                 if (datafellows & SSH_BUG_PKAUTH) {
 114                         buffer_put_char(&b, have_sig);
 115                 } else {
 116                         buffer_put_cstring(&b, "publickey");
 117                         buffer_put_char(&b, have_sig);
 118                         buffer_put_cstring(&b, pkalg);
 119                 }
 120                 buffer_put_string(&b, pkblob, blen);
 121 #ifdef DEBUG_PK
 122                 buffer_dump(&b);
 123 #endif
 124                 /* test for correct signature */
 125                 authenticated = 0;
 126                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 127                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 128                     buffer_len(&b))) == 1)
 129                         authenticated = 1;
 130                 buffer_free(&b);
 131                 xfree(sig);
 132         } else {
 133                 debug("test whether pkalg/pkblob are acceptable");
 134                 packet_check_eom();
 135
 136                 /* XXX fake reply and always send PK_OK ? */
 137                 /*
 138                  * XXX this allows testing whether a user is allowed
 139                  * to login: if you happen to have a valid pubkey this
 140                  * message is sent. the message is NEVER sent at all
 141                  * if a user is not allowed to login. is this an
 142                  * issue? -markus
 143                  */
 144                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 145                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 146                         packet_put_string(pkalg, alen);
 147                         packet_put_string(pkblob, blen);
 148                         packet_send();
 149                         packet_write_wait();
 150                         authctxt->postponed = 1;
 151                 }
 152         }
 153         if (authenticated != 1)
 154                 auth_clear_options();
 155 done:
 156         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 157         if (key != NULL)
 158                 key_free(key);
 159         xfree(pkalg);
 160         xfree(pkblob);
 161 #ifdef HAVE_CYGWIN
 162         if (check_nt_auth(0, authctxt->pw) == 0)
 163                 authenticated = 0;
 164 #endif
 165         return authenticated;
 166 }
 167
 168 /* return 1 if user allows given key */
 169 static int
 170 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 171 {
 172         char line[SSH_MAX_PUBKEY_BYTES];
 173         int found_key = 0;
 174         FILE *f;
 175         u_long linenum = 0;
 176         struct stat st;
 177         Key *found;
 178         char *fp;
 179
 180         /* Temporarily use the user's uid. */
 181         temporarily_use_uid(pw);
 182
 183         debug("trying public key file %s", file);
 184
 185         /* Fail quietly if file does not exist */
 186         if (stat(file, &st) < 0) {
 187                 /* Restore the privileged uid. */
 188                 restore_uid();
 189                 return 0;
 190         }
 191         /* Open the file containing the authorized keys. */
 192         f = fopen(file, "r");
 193         if (!f) {
 194                 /* Restore the privileged uid. */
 195                 restore_uid();
 196                 return 0;
 197         }
 198         if (options.strict_modes &&
 199             secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 200                 fclose(f);
 201                 logit("Authentication refused: %s", line);
 202                 restore_uid();
 203                 return 0;
 204         }
 205
 206         found_key = 0;
 207         found = key_new(key->type);
 208
 209         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 210                 char *cp, *key_options = NULL;
 211
 212                 /* Skip leading whitespace, empty and comment lines. */
 213                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 214                         ;
 215                 if (!*cp || *cp == '\n' || *cp == '#')
 216                         continue;
 217
 218                 if (key_read(found, &cp) != 1) {
 219                         /* no key?  check if there are options for this key */
 220                         int quoted = 0;
 221                         debug2("user_key_allowed: check options: '%s'", cp);
 222                         key_options = cp;
 223                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 224                                 if (*cp == '\\' && cp[1] == '"')
 225                                         cp++;   /* Skip both */
 226                                 else if (*cp == '"')
 227                                         quoted = !quoted;
 228                         }
 229                         /* Skip remaining whitespace. */
 230                         for (; *cp == ' ' || *cp == '\t'; cp++)
 231                                 ;
 232                         if (key_read(found, &cp) != 1) {
 233                                 debug2("user_key_allowed: advance: '%s'", cp);
 234                                 /* still no key?  advance to next line*/
 235                                 continue;
 236                         }
 237                 }
 238                 if (key_equal(found, key) &&
 239                     auth_parse_options(pw, key_options, file, linenum) == 1) {
 240                         found_key = 1;
 241                         debug("matching key found: file %s, line %lu",
 242                             file, linenum);
 243                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 244                         verbose("Found matching %s key: %s",
 245                             key_type(found), fp);
 246                         xfree(fp);
 247                         break;
 248                 }
 249         }
 250         restore_uid();
 251         fclose(f);
 252         key_free(found);
 253         if (!found_key)
 254                 debug2("key not found");
 255         return found_key;
 256 }
 257
 258 /* check whether given key is in .ssh/authorized_keys* */
 259 int
 260 user_key_allowed(struct passwd *pw, Key *key)
 261 {
 262         int success;
 263         char *file;
 264
 265         file = authorized_keys_file(pw);
 266         success = user_key_allowed2(pw, key, file);
 267         xfree(file);
 268         if (success)
 269                 return success;
 270
 271         /* try suffix "2" for backward compat, too */
 272         file = authorized_keys_file2(pw);
 273         success = user_key_allowed2(pw, key, file);
 274         xfree(file);
 275         return success;
 276 }
 277
 278 Authmethod method_pubkey = {
 279         "publickey",
 280         userauth_pubkey,
 281         &options.pubkey_authentication
 282 };