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 1.59 2004/07/28 09:40:29 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 "log.h"
  21 #include "servconf.h"
  22 #include "compat.h"
  23 #include "auth.h"
  24 #include "channels.h"
  25 #include "session.h"
  26 #include "uidswap.h"
  27 #include "monitor_wrap.h"
  28 #include "buffer.h"
  29
  30 /* import */
  31 extern ServerOptions options;
  32 extern Buffer loginmsg;
  33
  34 /*
  35  * convert ssh auth msg type into description
  36  */
  37 static char *
  38 get_authname(int type)
  39 {
  40         static char buf[1024];
  41         switch (type) {
  42         case SSH_CMSG_AUTH_PASSWORD:
  43                 return "password";
  44         case SSH_CMSG_AUTH_RSA:
  45                 return "rsa";
  46         case SSH_CMSG_AUTH_RHOSTS_RSA:
  47                 return "rhosts-rsa";
  48         case SSH_CMSG_AUTH_RHOSTS:
  49                 return "rhosts";
  50         case SSH_CMSG_AUTH_TIS:
  51         case SSH_CMSG_AUTH_TIS_RESPONSE:
  52                 return "challenge-response";
  53         }
  54         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  55         return buf;
  56 }
  57
  58 /*
  59  * read packets, try to authenticate the user and
  60  * return only if authentication is successful
  61  */
  62 static void
  63 do_authloop(Authctxt *authctxt)
  64 {
  65         int authenticated = 0;
  66         u_int bits;
  67         Key *client_host_key;
  68         BIGNUM *n;
  69         char *client_user, *password;
  70         char info[1024];
  71         u_int dlen;
  72         u_int ulen;
  73         int prev, type = 0;
  74
  75         debug("Attempting authentication for %s%.100s.",
  76             authctxt->valid ? "" : "invalid user ", authctxt->user);
  77
  78         /* If the user has no password, accept authentication immediately. */
  79         if (options.password_authentication &&
  80 #ifdef KRB5
  81             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  82 #endif
  83             PRIVSEP(auth_password(authctxt, ""))) {
  84 #ifdef USE_PAM
  85                 if (options.use_pam && (PRIVSEP(do_pam_account())))
  86 #endif
  87                 {
  88                         auth_log(authctxt, 1, "without authentication", "");
  89                         return;
  90                 }
  91         }
  92
  93         /* Indicate that authentication is needed. */
  94         packet_start(SSH_SMSG_FAILURE);
  95         packet_send();
  96         packet_write_wait();
  97
  98         client_user = NULL;
  99
 100         for (;;) {
 101                 /* default to fail */
 102                 authenticated = 0;
 103
 104                 info[0] = '\0';
 105
 106                 /* Get a packet from the client. */
 107                 prev = type;
 108                 type = packet_read();
 109
 110                 /*
 111                  * If we started challenge-response authentication but the
 112                  * next packet is not a response to our challenge, release
 113                  * the resources allocated by get_challenge() (which would
 114                  * normally have been released by verify_response() had we
 115                  * received such a response)
 116                  */
 117                 if (prev == SSH_CMSG_AUTH_TIS &&
 118                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 119                         abandon_challenge_response(authctxt);
 120
 121                 /* Process the packet. */
 122                 switch (type) {
 123                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 124                         if (!options.rhosts_rsa_authentication) {
 125                                 verbose("Rhosts with RSA authentication disabled.");
 126                                 break;
 127                         }
 128                         /*
 129                          * Get client user name.  Note that we just have to
 130                          * trust the client; root on the client machine can
 131                          * claim to be any user.
 132                          */
 133                         client_user = packet_get_string(&ulen);
 134
 135                         /* Get the client host key. */
 136                         client_host_key = key_new(KEY_RSA1);
 137                         bits = packet_get_int();
 138                         packet_get_bignum(client_host_key->rsa->e);
 139                         packet_get_bignum(client_host_key->rsa->n);
 140
 141                         if (bits != BN_num_bits(client_host_key->rsa->n))
 142                                 verbose("Warning: keysize mismatch for client_host_key: "
 143                                     "actual %d, announced %d",
 144                                     BN_num_bits(client_host_key->rsa->n), bits);
 145                         packet_check_eom();
 146
 147                         authenticated = auth_rhosts_rsa(authctxt, client_user,
 148                             client_host_key);
 149                         key_free(client_host_key);
 150
 151                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 152                         break;
 153
 154                 case SSH_CMSG_AUTH_RSA:
 155                         if (!options.rsa_authentication) {
 156                                 verbose("RSA authentication disabled.");
 157                                 break;
 158                         }
 159                         /* RSA authentication requested. */
 160                         if ((n = BN_new()) == NULL)
 161                                 fatal("do_authloop: BN_new failed");
 162                         packet_get_bignum(n);
 163                         packet_check_eom();
 164                         authenticated = auth_rsa(authctxt, n);
 165                         BN_clear_free(n);
 166                         break;
 167
 168                 case SSH_CMSG_AUTH_PASSWORD:
 169                         if (!options.password_authentication) {
 170                                 verbose("Password authentication disabled.");
 171                                 break;
 172                         }
 173                         /*
 174                          * Read user password.  It is in plain text, but was
 175                          * transmitted over the encrypted channel so it is
 176                          * not visible to an outside observer.
 177                          */
 178                         password = packet_get_string(&dlen);
 179                         packet_check_eom();
 180
 181                         /* Try authentication with the password. */
 182                         authenticated = PRIVSEP(auth_password(authctxt, password));
 183
 184                         memset(password, 0, strlen(password));
 185                         xfree(password);
 186                         break;
 187
 188                 case SSH_CMSG_AUTH_TIS:
 189                         debug("rcvd SSH_CMSG_AUTH_TIS");
 190                         if (options.challenge_response_authentication == 1) {
 191                                 char *challenge = get_challenge(authctxt);
 192                                 if (challenge != NULL) {
 193                                         debug("sending challenge '%s'", challenge);
 194                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 195                                         packet_put_cstring(challenge);
 196                                         xfree(challenge);
 197                                         packet_send();
 198                                         packet_write_wait();
 199                                         continue;
 200                                 }
 201                         }
 202                         break;
 203                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 204                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 205                         if (options.challenge_response_authentication == 1) {
 206                                 char *response = packet_get_string(&dlen);
 207                                 packet_check_eom();
 208                                 authenticated = verify_response(authctxt, response);
 209                                 memset(response, 'r', dlen);
 210                                 xfree(response);
 211                         }
 212                         break;
 213
 214                 default:
 215                         /*
 216                          * Any unknown messages will be ignored (and failure
 217                          * returned) during authentication.
 218                          */
 219                         logit("Unknown message during authentication: type %d", type);
 220                         break;
 221                 }
 222 #ifdef BSD_AUTH
 223                 if (authctxt->as) {
 224                         auth_close(authctxt->as);
 225                         authctxt->as = NULL;
 226                 }
 227 #endif
 228                 if (!authctxt->valid && authenticated)
 229                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 230                             authctxt->user);
 231
 232 #ifdef _UNICOS
 233                 if (authenticated && cray_access_denied(authctxt->user)) {
 234                         authenticated = 0;
 235                         fatal("Access denied for user %s.",authctxt->user);
 236                 }
 237 #endif /* _UNICOS */
 238
 239 #ifdef HAVE_CYGWIN
 240                 if (authenticated &&
 241                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
 242                     authctxt->pw)) {
 243                         packet_disconnect("Authentication rejected for uid %d.",
 244                             authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
 245                         authenticated = 0;
 246                 }
 247 #else
 248                 /* Special handling for root */
 249                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 250                     !auth_root_allowed(get_authname(type))) {
 251                         authenticated = 0;
 252 # ifdef SSH_AUDIT_EVENTS
 253                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 254 # endif
 255                 }
 256 #endif
 257
 258 #ifdef USE_PAM
 259                 if (options.use_pam && authenticated &&
 260                     !PRIVSEP(do_pam_account())) {
 261                         char *msg;
 262                         size_t len;
 263
 264                         error("Access denied for user %s by PAM account "
 265                            "configuration", authctxt->user);
 266                         len = buffer_len(&loginmsg);
 267                         buffer_append(&loginmsg, "\0", 1);
 268                         msg = buffer_ptr(&loginmsg);
 269                         /* strip trailing newlines */
 270                         if (len > 0)
 271                                 while (len > 0 && msg[--len] == '\n')
 272                                         msg[len] = '\0';
 273                         else
 274                                 msg = "Access denied.";
 275                         packet_disconnect(msg);
 276                 }
 277 #endif
 278
 279                 /* Log before sending the reply */
 280                 auth_log(authctxt, authenticated, get_authname(type), info);
 281
 282                 if (client_user != NULL) {
 283                         xfree(client_user);
 284                         client_user = NULL;
 285                 }
 286
 287                 if (authenticated)
 288                         return;
 289
 290                 if (authctxt->failures++ > options.max_authtries) {
 291 #ifdef SSH_AUDIT_EVENTS
 292                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 293 #endif
 294                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 295                 }
 296
 297                 packet_start(SSH_SMSG_FAILURE);
 298                 packet_send();
 299                 packet_write_wait();
 300         }
 301 }
 302
 303 /*
 304  * Performs authentication of an incoming connection.  Session key has already
 305  * been exchanged and encryption is enabled.
 306  */
 307 void
 308 do_authentication(Authctxt *authctxt)
 309 {
 310         u_int ulen;
 311         char *user, *style = NULL;
 312
 313         /* Get the name of the user that we wish to log in as. */
 314         packet_read_expect(SSH_CMSG_USER);
 315
 316         /* Get the user name. */
 317         user = packet_get_string(&ulen);
 318         packet_check_eom();
 319
 320         if ((style = strchr(user, ':')) != NULL)
 321                 *style++ = '\0';
 322
 323         authctxt->user = user;
 324         authctxt->style = style;
 325
 326         /* Verify that the user is a valid user. */
 327         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 328                 authctxt->valid = 1;
 329         else {
 330                 debug("do_authentication: invalid user %s", user);
 331                 authctxt->pw = fakepw();
 332         }
 333
 334         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 335             use_privsep ? " [net]" : "");
 336
 337 #ifdef USE_PAM
 338         if (options.use_pam)
 339                 PRIVSEP(start_pam(authctxt));
 340 #endif
 341
 342         /*
 343          * If we are not running as root, the user must have the same uid as
 344          * the server. (Unless you are running Windows)
 345          */
 346 #ifndef HAVE_CYGWIN
 347         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 348             authctxt->pw->pw_uid != getuid())
 349                 packet_disconnect("Cannot change user when server not running as root.");
 350 #endif
 351
 352         /*
 353          * Loop until the user has been authenticated or the connection is
 354          * closed, do_authloop() returns only if authentication is successful
 355          */
 356         do_authloop(authctxt);
 357
 358         /* The user has been authenticated and accepted. */
 359         packet_start(SSH_SMSG_SUCCESS);
 360         packet_send();
 361         packet_write_wait();
 362 }