auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.19 2008/07/03 21:46:58 otto Exp $ */
   2 /*
   3  * Copyright (c) 2000 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 <sys/types.h>
  29 #include <sys/stat.h>
  30
  31 #include <fcntl.h>
  32 #include <pwd.h>
  33 #include <stdio.h>
  34 #include <stdarg.h>
  35 #include <unistd.h>
  36
  37 #include "xmalloc.h"
  38 #include "ssh.h"
  39 #include "ssh2.h"
  40 #include "packet.h"
  41 #include "buffer.h"
  42 #include "log.h"
  43 #include "servconf.h"
  44 #include "compat.h"
  45 #include "key.h"
  46 #include "hostfile.h"
  47 #include "auth.h"
  48 #include "pathnames.h"
  49 #include "uidswap.h"
  50 #include "auth-options.h"
  51 #include "canohost.h"
  52 #ifdef GSSAPI
  53 #include "ssh-gss.h"
  54 #endif
  55 #include "monitor_wrap.h"
  56 #include "misc.h"
  57
  58 /* import */
  59 extern ServerOptions options;
  60 extern u_char *session_id2;
  61 extern u_int session_id2_len;
  62
  63 static int
  64 userauth_pubkey(Authctxt *authctxt)
  65 {
  66         Buffer b;
  67         Key *key = NULL;
  68         char *pkalg;
  69         u_char *pkblob, *sig;
  70         u_int alen, blen, slen;
  71         int have_sig, pktype;
  72         int authenticated = 0;
  73
  74         if (!authctxt->valid) {
  75                 debug2("userauth_pubkey: disabled because of invalid user");
  76                 return 0;
  77         }
  78         have_sig = packet_get_char();
  79         if (datafellows & SSH_BUG_PKAUTH) {
  80                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  81                 /* no explicit pkalg given */
  82                 pkblob = packet_get_string(&blen);
  83                 buffer_init(&b);
  84                 buffer_append(&b, pkblob, blen);
  85                 /* so we have to extract the pkalg from the pkblob */
  86                 pkalg = buffer_get_string(&b, &alen);
  87                 buffer_free(&b);
  88         } else {
  89                 pkalg = packet_get_string(&alen);
  90                 pkblob = packet_get_string(&blen);
  91         }
  92         pktype = key_type_from_name(pkalg);
  93         if (pktype == KEY_UNSPEC) {
  94                 /* this is perfectly legal */
  95                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  96                     pkalg);
  97                 goto done;
  98         }
  99         key = key_from_blob(pkblob, blen);
 100         if (key == NULL) {
 101                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 102                 goto done;
 103         }
 104         if (key->type != pktype) {
 105                 error("userauth_pubkey: type mismatch for decoded key "
 106                     "(received %d, expected %d)", key->type, pktype);
 107                 goto done;
 108         }
 109         if (have_sig) {
 110                 sig = packet_get_string(&slen);
 111                 packet_check_eom();
 112                 buffer_init(&b);
 113                 if (datafellows & SSH_OLD_SESSIONID) {
 114                         buffer_append(&b, session_id2, session_id2_len);
 115                 } else {
 116                         buffer_put_string(&b, session_id2, session_id2_len);
 117                 }
 118                 /* reconstruct packet */
 119                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 120                 buffer_put_cstring(&b, authctxt->user);
 121                 buffer_put_cstring(&b,
 122                     datafellows & SSH_BUG_PKSERVICE ?
 123                     "ssh-userauth" :
 124                     authctxt->service);
 125                 if (datafellows & SSH_BUG_PKAUTH) {
 126                         buffer_put_char(&b, have_sig);
 127                 } else {
 128                         buffer_put_cstring(&b, "publickey");
 129                         buffer_put_char(&b, have_sig);
 130                         buffer_put_cstring(&b, pkalg);
 131                 }
 132                 buffer_put_string(&b, pkblob, blen);
 133 #ifdef DEBUG_PK
 134                 buffer_dump(&b);
 135 #endif
 136                 /* test for correct signature */
 137                 authenticated = 0;
 138                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 139                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 140                     buffer_len(&b))) == 1)
 141                         authenticated = 1;
 142                 buffer_free(&b);
 143                 xfree(sig);
 144         } else {
 145                 debug("test whether pkalg/pkblob are acceptable");
 146                 packet_check_eom();
 147
 148                 /* XXX fake reply and always send PK_OK ? */
 149                 /*
 150                  * XXX this allows testing whether a user is allowed
 151                  * to login: if you happen to have a valid pubkey this
 152                  * message is sent. the message is NEVER sent at all
 153                  * if a user is not allowed to login. is this an
 154                  * issue? -markus
 155                  */
 156                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 157                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 158                         packet_put_string(pkalg, alen);
 159                         packet_put_string(pkblob, blen);
 160                         packet_send();
 161                         packet_write_wait();
 162                         authctxt->postponed = 1;
 163                 }
 164         }
 165         if (authenticated != 1)
 166                 auth_clear_options();
 167 done:
 168         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 169         if (key != NULL)
 170                 key_free(key);
 171         xfree(pkalg);
 172         xfree(pkblob);
 173         return authenticated;
 174 }
 175
 176 /* return 1 if user allows given key */
 177 static int
 178 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 179 {
 180         char line[SSH_MAX_PUBKEY_BYTES];
 181         int found_key = 0;
 182         FILE *f;
 183         u_long linenum = 0;
 184         Key *found;
 185         char *fp;
 186
 187         /* Temporarily use the user's uid. */
 188         temporarily_use_uid(pw);
 189
 190         debug("trying public key file %s", file);
 191         f = auth_openkeyfile(file, pw, options.strict_modes);
 192
 193         if (!f) {
 194                 restore_uid();
 195                 return 0;
 196         }
 197
 198         found_key = 0;
 199         found = key_new(key->type);
 200
 201         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 202                 char *cp, *key_options = NULL;
 203
 204                 /* Skip leading whitespace, empty and comment lines. */
 205                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 206                         ;
 207                 if (!*cp || *cp == '\n' || *cp == '#')
 208                         continue;
 209
 210                 if (key_read(found, &cp) != 1) {
 211                         /* no key?  check if there are options for this key */
 212                         int quoted = 0;
 213                         debug2("user_key_allowed: check options: '%s'", cp);
 214                         key_options = cp;
 215                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 216                                 if (*cp == '\\' && cp[1] == '"')
 217                                         cp++;   /* Skip both */
 218                                 else if (*cp == '"')
 219                                         quoted = !quoted;
 220                         }
 221                         /* Skip remaining whitespace. */
 222                         for (; *cp == ' ' || *cp == '\t'; cp++)
 223                                 ;
 224                         if (key_read(found, &cp) != 1) {
 225                                 debug2("user_key_allowed: advance: '%s'", cp);
 226                                 /* still no key?  advance to next line*/
 227                                 continue;
 228                         }
 229                 }
 230                 if (key_equal(found, key) &&
 231                     auth_parse_options(pw, key_options, file, linenum) == 1) {
 232                         found_key = 1;
 233                         debug("matching key found: file %s, line %lu",
 234                             file, linenum);
 235                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 236                         verbose("Found matching %s key: %s",
 237                             key_type(found), fp);
 238                         xfree(fp);
 239                         break;
 240                 }
 241         }
 242         restore_uid();
 243         fclose(f);
 244         key_free(found);
 245         if (!found_key)
 246                 debug2("key not found");
 247         return found_key;
 248 }
 249
 250 /* check whether given key is in .ssh/authorized_keys* */
 251 int
 252 user_key_allowed(struct passwd *pw, Key *key)
 253 {
 254         int success;
 255         char *file;
 256
 257         file = authorized_keys_file(pw);
 258         success = user_key_allowed2(pw, key, file);
 259         xfree(file);
 260         if (success)
 261                 return success;
 262
 263         /* try suffix "2" for backward compat, too */
 264         file = authorized_keys_file2(pw);
 265         success = user_key_allowed2(pw, key, file);
 266         xfree(file);
 267         return success;
 268 }
 269
 270 Authmethod method_pubkey = {
 271         "publickey",
 272         userauth_pubkey,
 273         &options.pubkey_authentication
 274 };