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 1.56 2004/05/09 01:19:27 djm 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
  29 /* import */
  30 extern ServerOptions options;
  31
  32 /*
  33  * convert ssh auth msg type into description
  34  */
  35 static char *
  36 get_authname(int type)
  37 {
  38         static char buf[1024];
  39         switch (type) {
  40         case SSH_CMSG_AUTH_PASSWORD:
  41                 return "password";
  42         case SSH_CMSG_AUTH_RSA:
  43                 return "rsa";
  44         case SSH_CMSG_AUTH_RHOSTS_RSA:
  45                 return "rhosts-rsa";
  46         case SSH_CMSG_AUTH_RHOSTS:
  47                 return "rhosts";
  48         case SSH_CMSG_AUTH_TIS:
  49         case SSH_CMSG_AUTH_TIS_RESPONSE:
  50                 return "challenge-response";
  51         }
  52         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  53         return buf;
  54 }
  55
  56 /*
  57  * read packets, try to authenticate the user and
  58  * return only if authentication is successful
  59  */
  60 static void
  61 do_authloop(Authctxt *authctxt)
  62 {
  63         int authenticated = 0;
  64         u_int bits;
  65         Key *client_host_key;
  66         BIGNUM *n;
  67         char *client_user, *password;
  68         char info[1024];
  69         u_int dlen;
  70         u_int ulen;
  71         int prev, type = 0;
  72         struct passwd *pw = authctxt->pw;
  73
  74         debug("Attempting authentication for %s%.100s.",
  75             authctxt->valid ? "" : "illegal user ", authctxt->user);
  76
  77         /* If the user has no password, accept authentication immediately. */
  78         if (options.password_authentication &&
  79 #ifdef KRB5
  80             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  81 #endif
  82             PRIVSEP(auth_password(authctxt, ""))) {
  83                 auth_log(authctxt, 1, "without authentication", "");
  84                 return;
  85         }
  86
  87         /* Indicate that authentication is needed. */
  88         packet_start(SSH_SMSG_FAILURE);
  89         packet_send();
  90         packet_write_wait();
  91
  92         client_user = NULL;
  93
  94         for (;;) {
  95                 /* default to fail */
  96                 authenticated = 0;
  97
  98                 info[0] = '\0';
  99
 100                 /* Get a packet from the client. */
 101                 prev = type;
 102                 type = packet_read();
 103
 104                 /*
 105                  * If we started challenge-response authentication but the
 106                  * next packet is not a response to our challenge, release
 107                  * the resources allocated by get_challenge() (which would
 108                  * normally have been released by verify_response() had we
 109                  * received such a response)
 110                  */
 111                 if (prev == SSH_CMSG_AUTH_TIS &&
 112                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 113                         abandon_challenge_response(authctxt);
 114
 115                 /* Process the packet. */
 116                 switch (type) {
 117                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 118                         if (!options.rhosts_rsa_authentication) {
 119                                 verbose("Rhosts with RSA authentication disabled.");
 120                                 break;
 121                         }
 122                         /*
 123                          * Get client user name.  Note that we just have to
 124                          * trust the client; root on the client machine can
 125                          * claim to be any user.
 126                          */
 127                         client_user = packet_get_string(&ulen);
 128
 129                         /* Get the client host key. */
 130                         client_host_key = key_new(KEY_RSA1);
 131                         bits = packet_get_int();
 132                         packet_get_bignum(client_host_key->rsa->e);
 133                         packet_get_bignum(client_host_key->rsa->n);
 134
 135                         if (bits != BN_num_bits(client_host_key->rsa->n))
 136                                 verbose("Warning: keysize mismatch for client_host_key: "
 137                                     "actual %d, announced %d",
 138                                     BN_num_bits(client_host_key->rsa->n), bits);
 139                         packet_check_eom();
 140
 141                         authenticated = auth_rhosts_rsa(authctxt, client_user,
 142                             client_host_key);
 143                         key_free(client_host_key);
 144
 145                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 146                         break;
 147
 148                 case SSH_CMSG_AUTH_RSA:
 149                         if (!options.rsa_authentication) {
 150                                 verbose("RSA authentication disabled.");
 151                                 break;
 152                         }
 153                         /* RSA authentication requested. */
 154                         if ((n = BN_new()) == NULL)
 155                                 fatal("do_authloop: BN_new failed");
 156                         packet_get_bignum(n);
 157                         packet_check_eom();
 158                         authenticated = auth_rsa(authctxt, n);
 159                         BN_clear_free(n);
 160                         break;
 161
 162                 case SSH_CMSG_AUTH_PASSWORD:
 163                         if (!options.password_authentication) {
 164                                 verbose("Password authentication disabled.");
 165                                 break;
 166                         }
 167                         /*
 168                          * Read user password.  It is in plain text, but was
 169                          * transmitted over the encrypted channel so it is
 170                          * not visible to an outside observer.
 171                          */
 172                         password = packet_get_string(&dlen);
 173                         packet_check_eom();
 174
 175                         /* Try authentication with the password. */
 176                         authenticated = PRIVSEP(auth_password(authctxt, password));
 177
 178                         memset(password, 0, strlen(password));
 179                         xfree(password);
 180                         break;
 181
 182                 case SSH_CMSG_AUTH_TIS:
 183                         debug("rcvd SSH_CMSG_AUTH_TIS");
 184                         if (options.challenge_response_authentication == 1) {
 185                                 char *challenge = get_challenge(authctxt);
 186                                 if (challenge != NULL) {
 187                                         debug("sending challenge '%s'", challenge);
 188                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 189                                         packet_put_cstring(challenge);
 190                                         xfree(challenge);
 191                                         packet_send();
 192                                         packet_write_wait();
 193                                         continue;
 194                                 }
 195                         }
 196                         break;
 197                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 198                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 199                         if (options.challenge_response_authentication == 1) {
 200                                 char *response = packet_get_string(&dlen);
 201                                 packet_check_eom();
 202                                 authenticated = verify_response(authctxt, response);
 203                                 memset(response, 'r', dlen);
 204                                 xfree(response);
 205                         }
 206                         break;
 207
 208                 default:
 209                         /*
 210                          * Any unknown messages will be ignored (and failure
 211                          * returned) during authentication.
 212                          */
 213                         logit("Unknown message during authentication: type %d", type);
 214                         break;
 215                 }
 216 #ifdef BSD_AUTH
 217                 if (authctxt->as) {
 218                         auth_close(authctxt->as);
 219                         authctxt->as = NULL;
 220                 }
 221 #endif
 222                 if (!authctxt->valid && authenticated)
 223                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 224                             authctxt->user);
 225
 226 #ifdef _UNICOS
 227                 if (authenticated && cray_access_denied(authctxt->user)) {
 228                         authenticated = 0;
 229                         fatal("Access denied for user %s.",authctxt->user);
 230                 }
 231 #endif /* _UNICOS */
 232
 233 #ifdef HAVE_CYGWIN
 234                 if (authenticated &&
 235                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 236                         packet_disconnect("Authentication rejected for uid %d.",
 237                             pw == NULL ? -1 : pw->pw_uid);
 238                         authenticated = 0;
 239                 }
 240 #else
 241                 /* Special handling for root */
 242                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 243                     !auth_root_allowed(get_authname(type)))
 244                         authenticated = 0;
 245 #endif
 246
 247 #ifdef USE_PAM
 248                 if (options.use_pam && authenticated &&
 249                     !PRIVSEP(do_pam_account()))
 250                         authenticated = 0;
 251 #endif
 252
 253                 /* Log before sending the reply */
 254                 auth_log(authctxt, authenticated, get_authname(type), info);
 255
 256                 if (client_user != NULL) {
 257                         xfree(client_user);
 258                         client_user = NULL;
 259                 }
 260
 261                 if (authenticated)
 262                         return;
 263
 264                 if (authctxt->failures++ > AUTH_FAIL_MAX)
 265                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 266
 267                 packet_start(SSH_SMSG_FAILURE);
 268                 packet_send();
 269                 packet_write_wait();
 270         }
 271 }
 272
 273 /*
 274  * Performs authentication of an incoming connection.  Session key has already
 275  * been exchanged and encryption is enabled.
 276  */
 277 void
 278 do_authentication(Authctxt *authctxt)
 279 {
 280         u_int ulen;
 281         char *user, *style = NULL;
 282
 283         /* Get the name of the user that we wish to log in as. */
 284         packet_read_expect(SSH_CMSG_USER);
 285
 286         /* Get the user name. */
 287         user = packet_get_string(&ulen);
 288         packet_check_eom();
 289
 290         if ((style = strchr(user, ':')) != NULL)
 291                 *style++ = '\0';
 292
 293         authctxt->user = user;
 294         authctxt->style = style;
 295
 296         /* Verify that the user is a valid user. */
 297         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 298                 authctxt->valid = 1;
 299         else {
 300                 debug("do_authentication: illegal user %s", user);
 301                 authctxt->pw = fakepw();
 302         }
 303
 304         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 305             use_privsep ? " [net]" : "");
 306
 307 #ifdef USE_PAM
 308         if (options.use_pam)
 309                 PRIVSEP(start_pam(authctxt));
 310 #endif
 311
 312         /*
 313          * If we are not running as root, the user must have the same uid as
 314          * the server. (Unless you are running Windows)
 315          */
 316 #ifndef HAVE_CYGWIN
 317         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 318             authctxt->pw->pw_uid != getuid())
 319                 packet_disconnect("Cannot change user when server not running as root.");
 320 #endif
 321
 322         /*
 323          * Loop until the user has been authenticated or the connection is
 324          * closed, do_authloop() returns only if authentication is successful
 325          */
 326         do_authloop(authctxt);
 327
 328         /* The user has been authenticated and accepted. */
 329         packet_start(SSH_SMSG_SUCCESS);
 330         packet_send();
 331         packet_write_wait();
 332 }