auth1.c

   1 /*
   2  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   3  *                    All rights reserved
   4  *
   5  * As far as I am concerned, the code I have written for this software
   6  * can be used freely for any purpose.  Any derived versions of this
   7  * software must be clearly marked as such, and if the derived work is
   8  * incompatible with the protocol description in the RFC file, it must be
   9  * called by a name other than "ssh" or "Secure Shell".
  10  */
  11
  12 #include "includes.h"
  13 RCSID("$OpenBSD: auth1.c,v 1.50 2003/08/13 08:46:30 markus Exp $");
  14
  15 #include "xmalloc.h"
  16 #include "rsa.h"
  17 #include "ssh1.h"
  18 #include "packet.h"
  19 #include "buffer.h"
  20 #include "mpaux.h"
  21 #include "log.h"
  22 #include "servconf.h"
  23 #include "compat.h"
  24 #include "auth.h"
  25 #include "channels.h"
  26 #include "session.h"
  27 #include "uidswap.h"
  28 #include "monitor_wrap.h"
  29
  30 /* import */
  31 extern ServerOptions options;
  32
  33 /*
  34  * convert ssh auth msg type into description
  35  */
  36 static char *
  37 get_authname(int type)
  38 {
  39         static char buf[1024];
  40         switch (type) {
  41         case SSH_CMSG_AUTH_PASSWORD:
  42                 return "password";
  43         case SSH_CMSG_AUTH_RSA:
  44                 return "rsa";
  45         case SSH_CMSG_AUTH_RHOSTS_RSA:
  46                 return "rhosts-rsa";
  47         case SSH_CMSG_AUTH_RHOSTS:
  48                 return "rhosts";
  49         case SSH_CMSG_AUTH_TIS:
  50         case SSH_CMSG_AUTH_TIS_RESPONSE:
  51                 return "challenge-response";
  52 #ifdef KRB5
  53         case SSH_CMSG_AUTH_KERBEROS:
  54                 return "kerberos";
  55 #endif
  56         }
  57         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  58         return buf;
  59 }
  60
  61 /*
  62  * read packets, try to authenticate the user and
  63  * return only if authentication is successful
  64  */
  65 static void
  66 do_authloop(Authctxt *authctxt)
  67 {
  68         int authenticated = 0;
  69         u_int bits;
  70         Key *client_host_key;
  71         BIGNUM *n;
  72         char *client_user, *password;
  73         char info[1024];
  74         u_int dlen;
  75         u_int ulen;
  76         int prev, type = 0;
  77         struct passwd *pw = authctxt->pw;
  78
  79         debug("Attempting authentication for %s%.100s.",
  80             authctxt->valid ? "" : "illegal user ", authctxt->user);
  81
  82         /* If the user has no password, accept authentication immediately. */
  83         if (options.password_authentication &&
  84 #ifdef KRB5
  85             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  86 #endif
  87             PRIVSEP(auth_password(authctxt, ""))) {
  88                 auth_log(authctxt, 1, "without authentication", "");
  89                 return;
  90         }
  91
  92         /* Indicate that authentication is needed. */
  93         packet_start(SSH_SMSG_FAILURE);
  94         packet_send();
  95         packet_write_wait();
  96
  97         client_user = NULL;
  98
  99         for (;;) {
 100                 /* default to fail */
 101                 authenticated = 0;
 102
 103                 info[0] = '\0';
 104
 105                 /* Get a packet from the client. */
 106                 prev = type;
 107                 type = packet_read();
 108
 109                 /*
 110                  * If we started challenge-response authentication but the
 111                  * next packet is not a response to our challenge, release
 112                  * the resources allocated by get_challenge() (which would
 113                  * normally have been released by verify_response() had we
 114                  * received such a response)
 115                  */
 116                 if (prev == SSH_CMSG_AUTH_TIS &&
 117                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 118                         abandon_challenge_response(authctxt);
 119
 120                 /* Process the packet. */
 121                 switch (type) {
 122
 123 #ifdef KRB5
 124                 case SSH_CMSG_AUTH_KERBEROS:
 125                         if (!options.kerberos_authentication) {
 126                                 verbose("Kerberos authentication disabled.");
 127                         } else {
 128                                 char *kdata = packet_get_string(&dlen);
 129                                 packet_check_eom();
 130
 131                                 if (kdata[0] != 4) { /* KRB_PROT_VERSION */
 132                                         krb5_data tkt, reply;
 133                                         tkt.length = dlen;
 134                                         tkt.data = kdata;
 135
 136                                         if (PRIVSEP(auth_krb5(authctxt, &tkt,
 137                                             &client_user, &reply))) {
 138                                                 authenticated = 1;
 139                                                 snprintf(info, sizeof(info),
 140                                                     " tktuser %.100s",
 141                                                     client_user);
 142
 143                                                 /* Send response to client */
 144                                                 packet_start(
 145                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 146                                                 packet_put_string((char *)
 147                                                     reply.data, reply.length);
 148                                                 packet_send();
 149                                                 packet_write_wait();
 150
 151                                                 if (reply.length)
 152                                                         xfree(reply.data);
 153                                         }
 154                                 }
 155                                 xfree(kdata);
 156                         }
 157                         break;
 158                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 159                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 160                         break;
 161 #endif
 162
 163                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 164                         if (!options.rhosts_rsa_authentication) {
 165                                 verbose("Rhosts with RSA authentication disabled.");
 166                                 break;
 167                         }
 168                         /*
 169                          * Get client user name.  Note that we just have to
 170                          * trust the client; root on the client machine can
 171                          * claim to be any user.
 172                          */
 173                         client_user = packet_get_string(&ulen);
 174
 175                         /* Get the client host key. */
 176                         client_host_key = key_new(KEY_RSA1);
 177                         bits = packet_get_int();
 178                         packet_get_bignum(client_host_key->rsa->e);
 179                         packet_get_bignum(client_host_key->rsa->n);
 180
 181                         if (bits != BN_num_bits(client_host_key->rsa->n))
 182                                 verbose("Warning: keysize mismatch for client_host_key: "
 183                                     "actual %d, announced %d",
 184                                     BN_num_bits(client_host_key->rsa->n), bits);
 185                         packet_check_eom();
 186
 187                         authenticated = auth_rhosts_rsa(pw, client_user,
 188                             client_host_key);
 189                         key_free(client_host_key);
 190
 191                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 192                         break;
 193
 194                 case SSH_CMSG_AUTH_RSA:
 195                         if (!options.rsa_authentication) {
 196                                 verbose("RSA authentication disabled.");
 197                                 break;
 198                         }
 199                         /* RSA authentication requested. */
 200                         if ((n = BN_new()) == NULL)
 201                                 fatal("do_authloop: BN_new failed");
 202                         packet_get_bignum(n);
 203                         packet_check_eom();
 204                         authenticated = auth_rsa(pw, n);
 205                         BN_clear_free(n);
 206                         break;
 207
 208                 case SSH_CMSG_AUTH_PASSWORD:
 209                         if (!options.password_authentication) {
 210                                 verbose("Password authentication disabled.");
 211                                 break;
 212                         }
 213                         /*
 214                          * Read user password.  It is in plain text, but was
 215                          * transmitted over the encrypted channel so it is
 216                          * not visible to an outside observer.
 217                          */
 218                         password = packet_get_string(&dlen);
 219                         packet_check_eom();
 220
 221                         /* Try authentication with the password. */
 222                         authenticated = PRIVSEP(auth_password(authctxt, password));
 223
 224                         memset(password, 0, strlen(password));
 225                         xfree(password);
 226                         break;
 227
 228                 case SSH_CMSG_AUTH_TIS:
 229                         debug("rcvd SSH_CMSG_AUTH_TIS");
 230                         if (options.challenge_response_authentication == 1) {
 231                                 char *challenge = get_challenge(authctxt);
 232                                 if (challenge != NULL) {
 233                                         debug("sending challenge '%s'", challenge);
 234                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 235                                         packet_put_cstring(challenge);
 236                                         xfree(challenge);
 237                                         packet_send();
 238                                         packet_write_wait();
 239                                         continue;
 240                                 }
 241                         }
 242                         break;
 243                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 244                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 245                         if (options.challenge_response_authentication == 1) {
 246                                 char *response = packet_get_string(&dlen);
 247                                 packet_check_eom();
 248                                 authenticated = verify_response(authctxt, response);
 249                                 memset(response, 'r', dlen);
 250                                 xfree(response);
 251                         }
 252                         break;
 253
 254                 default:
 255                         /*
 256                          * Any unknown messages will be ignored (and failure
 257                          * returned) during authentication.
 258                          */
 259                         logit("Unknown message during authentication: type %d", type);
 260                         break;
 261                 }
 262 #ifdef BSD_AUTH
 263                 if (authctxt->as) {
 264                         auth_close(authctxt->as);
 265                         authctxt->as = NULL;
 266                 }
 267 #endif
 268                 if (!authctxt->valid && authenticated)
 269                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 270                             authctxt->user);
 271
 272 #ifdef _UNICOS
 273                 if (authenticated && cray_access_denied(authctxt->user)) {
 274                         authenticated = 0;
 275                         fatal("Access denied for user %s.",authctxt->user);
 276                 }
 277 #endif /* _UNICOS */
 278
 279 #ifdef HAVE_CYGWIN
 280                 if (authenticated &&
 281                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 282                         packet_disconnect("Authentication rejected for uid %d.",
 283                         pw == NULL ? -1 : pw->pw_uid);
 284                         authenticated = 0;
 285                 }
 286 #else
 287                 /* Special handling for root */
 288                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 289                     !auth_root_allowed(get_authname(type)))
 290                         authenticated = 0;
 291 #endif
 292
 293                 /* Log before sending the reply */
 294                 auth_log(authctxt, authenticated, get_authname(type), info);
 295
 296                 if (client_user != NULL) {
 297                         xfree(client_user);
 298                         client_user = NULL;
 299                 }
 300
 301                 if (authenticated)
 302                         return;
 303
 304                 if (authctxt->failures++ > AUTH_FAIL_MAX)
 305                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 306
 307                 packet_start(SSH_SMSG_FAILURE);
 308                 packet_send();
 309                 packet_write_wait();
 310         }
 311 }
 312
 313 /*
 314  * Performs authentication of an incoming connection.  Session key has already
 315  * been exchanged and encryption is enabled.
 316  */
 317 Authctxt *
 318 do_authentication(void)
 319 {
 320         Authctxt *authctxt;
 321         u_int ulen;
 322         char *user, *style = NULL;
 323
 324         /* Get the name of the user that we wish to log in as. */
 325         packet_read_expect(SSH_CMSG_USER);
 326
 327         /* Get the user name. */
 328         user = packet_get_string(&ulen);
 329         packet_check_eom();
 330
 331         if ((style = strchr(user, ':')) != NULL)
 332                 *style++ = '\0';
 333
 334 #ifdef KRB5
 335         /* XXX - SSH.com Kerberos v5 braindeath. */
 336         if ((datafellows & SSH_BUG_K5USER) &&
 337             options.kerberos_authentication) {
 338                 char *p;
 339                 if ((p = strchr(user, '@')) != NULL)
 340                         *p = '\0';
 341         }
 342 #endif
 343
 344         authctxt = authctxt_new();
 345         authctxt->user = user;
 346         authctxt->style = style;
 347
 348         /* Verify that the user is a valid user. */
 349         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 350                 authctxt->valid = 1;
 351         else
 352                 debug("do_authentication: illegal user %s", user);
 353
 354         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 355             use_privsep ? " [net]" : "");
 356
 357 #ifdef USE_PAM
 358         if (options.use_pam)
 359                 PRIVSEP(start_pam(user));
 360 #endif
 361
 362         /*
 363          * If we are not running as root, the user must have the same uid as
 364          * the server. (Unless you are running Windows)
 365          */
 366 #ifndef HAVE_CYGWIN
 367         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 368             authctxt->pw->pw_uid != getuid())
 369                 packet_disconnect("Cannot change user when server not running as root.");
 370 #endif
 371
 372         /*
 373          * Loop until the user has been authenticated or the connection is
 374          * closed, do_authloop() returns only if authentication is successful
 375          */
 376         do_authloop(authctxt);
 377
 378         /* The user has been authenticated and accepted. */
 379         packet_start(SSH_SMSG_SUCCESS);
 380         packet_send();
 381         packet_write_wait();
 382
 383         return (authctxt);
 384 }