auth1.c

   1 /* $OpenBSD: auth1.c,v 1.66 2006/03/25 13:17:01 djm Exp $ */
   2 /*
   3  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   4  *                    All rights reserved
   5  *
   6  * As far as I am concerned, the code I have written for this software
   7  * can be used freely for any purpose.  Any derived versions of this
   8  * software must be clearly marked as such, and if the derived work is
   9  * incompatible with the protocol description in the RFC file, it must be
  10  * called by a name other than "ssh" or "Secure Shell".
  11  */
  12
  13 #include "includes.h"
  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 static int auth1_process_password(Authctxt *, char *, size_t);
  35 static int auth1_process_rsa(Authctxt *, char *, size_t);
  36 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
  37 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
  38 static int auth1_process_tis_response(Authctxt *, char *, size_t);
  39
  40 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  41
  42 struct AuthMethod1 {
  43         int type;
  44         char *name;
  45         int *enabled;
  46         int (*method)(Authctxt *, char *, size_t);
  47 };
  48
  49 const struct AuthMethod1 auth1_methods[] = {
  50         {
  51                 SSH_CMSG_AUTH_PASSWORD, "password",
  52                 &options.password_authentication, auth1_process_password
  53         },
  54         {
  55                 SSH_CMSG_AUTH_RSA, "rsa",
  56                 &options.rsa_authentication, auth1_process_rsa
  57         },
  58         {
  59                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  60                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  61         },
  62         {
  63                 SSH_CMSG_AUTH_TIS, "challenge-response",
  64                 &options.challenge_response_authentication,
  65                 auth1_process_tis_challenge
  66         },
  67         {
  68                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  69                 &options.challenge_response_authentication,
  70                 auth1_process_tis_response
  71         },
  72         { -1, NULL, NULL, NULL}
  73 };
  74
  75 static const struct AuthMethod1
  76 *lookup_authmethod1(int type)
  77 {
  78         int i;
  79
  80         for (i = 0; auth1_methods[i].name != NULL; i++)
  81                 if (auth1_methods[i].type == type)
  82                         return (&(auth1_methods[i]));
  83
  84         return (NULL);
  85 }
  86
  87 static char *
  88 get_authname(int type)
  89 {
  90         const struct AuthMethod1 *a;
  91         static char buf[64];
  92
  93         if ((a = lookup_authmethod1(type)) != NULL)
  94                 return (a->name);
  95         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
  96         return (buf);
  97 }
  98
  99 /*ARGSUSED*/
 100 static int
 101 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 102 {
 103         int authenticated = 0;
 104         char *password;
 105         u_int dlen;
 106
 107         /*
 108          * Read user password.  It is in plain text, but was
 109          * transmitted over the encrypted channel so it is
 110          * not visible to an outside observer.
 111          */
 112         password = packet_get_string(&dlen);
 113         packet_check_eom();
 114
 115         /* Try authentication with the password. */
 116         authenticated = PRIVSEP(auth_password(authctxt, password));
 117
 118         memset(password, 0, dlen);
 119         xfree(password);
 120
 121         return (authenticated);
 122 }
 123
 124 /*ARGSUSED*/
 125 static int
 126 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 127 {
 128         int authenticated = 0;
 129         BIGNUM *n;
 130
 131         /* RSA authentication requested. */
 132         if ((n = BN_new()) == NULL)
 133                 fatal("do_authloop: BN_new failed");
 134         packet_get_bignum(n);
 135         packet_check_eom();
 136         authenticated = auth_rsa(authctxt, n);
 137         BN_clear_free(n);
 138
 139         return (authenticated);
 140 }
 141
 142 /*ARGSUSED*/
 143 static int
 144 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 145 {
 146         int keybits, authenticated = 0;
 147         u_int bits;
 148         Key *client_host_key;
 149         u_int ulen;
 150
 151         /*
 152          * Get client user name.  Note that we just have to
 153          * trust the client; root on the client machine can
 154          * claim to be any user.
 155          */
 156         client_user = packet_get_string(&ulen);
 157
 158         /* Get the client host key. */
 159         client_host_key = key_new(KEY_RSA1);
 160         bits = packet_get_int();
 161         packet_get_bignum(client_host_key->rsa->e);
 162         packet_get_bignum(client_host_key->rsa->n);
 163
 164         keybits = BN_num_bits(client_host_key->rsa->n);
 165         if (keybits < 0 || bits != (u_int)keybits) {
 166                 verbose("Warning: keysize mismatch for client_host_key: "
 167                     "actual %d, announced %d",
 168                     BN_num_bits(client_host_key->rsa->n), bits);
 169         }
 170         packet_check_eom();
 171
 172         authenticated = auth_rhosts_rsa(authctxt, client_user,
 173             client_host_key);
 174         key_free(client_host_key);
 175
 176         snprintf(info, infolen, " ruser %.100s", client_user);
 177
 178         return (authenticated);
 179 }
 180
 181 /*ARGSUSED*/
 182 static int
 183 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 184 {
 185         char *challenge;
 186
 187         if ((challenge = get_challenge(authctxt)) == NULL)
 188                 return (0);
 189
 190         debug("sending challenge '%s'", challenge);
 191         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 192         packet_put_cstring(challenge);
 193         xfree(challenge);
 194         packet_send();
 195         packet_write_wait();
 196
 197         return (-1);
 198 }
 199
 200 /*ARGSUSED*/
 201 static int
 202 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 203 {
 204         int authenticated = 0;
 205         char *response;
 206         u_int dlen;
 207
 208         response = packet_get_string(&dlen);
 209         packet_check_eom();
 210         authenticated = verify_response(authctxt, response);
 211         memset(response, 'r', dlen);
 212         xfree(response);
 213
 214         return (authenticated);
 215 }
 216
 217 /*
 218  * read packets, try to authenticate the user and
 219  * return only if authentication is successful
 220  */
 221 static void
 222 do_authloop(Authctxt *authctxt)
 223 {
 224         int authenticated = 0;
 225         char info[1024];
 226         int prev = 0, type = 0;
 227         const struct AuthMethod1 *meth;
 228
 229         debug("Attempting authentication for %s%.100s.",
 230             authctxt->valid ? "" : "invalid user ", authctxt->user);
 231
 232         /* If the user has no password, accept authentication immediately. */
 233         if (options.password_authentication &&
 234 #ifdef KRB5
 235             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 236 #endif
 237             PRIVSEP(auth_password(authctxt, ""))) {
 238 #ifdef USE_PAM
 239                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 240 #endif
 241                 {
 242                         auth_log(authctxt, 1, "without authentication", "");
 243                         return;
 244                 }
 245         }
 246
 247         /* Indicate that authentication is needed. */
 248         packet_start(SSH_SMSG_FAILURE);
 249         packet_send();
 250         packet_write_wait();
 251
 252         for (;;) {
 253                 /* default to fail */
 254                 authenticated = 0;
 255
 256                 info[0] = '\0';
 257
 258                 /* Get a packet from the client. */
 259                 prev = type;
 260                 type = packet_read();
 261
 262                 /*
 263                  * If we started challenge-response authentication but the
 264                  * next packet is not a response to our challenge, release
 265                  * the resources allocated by get_challenge() (which would
 266                  * normally have been released by verify_response() had we
 267                  * received such a response)
 268                  */
 269                 if (prev == SSH_CMSG_AUTH_TIS &&
 270                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 271                         abandon_challenge_response(authctxt);
 272
 273                 if ((meth = lookup_authmethod1(type)) == NULL) {
 274                         logit("Unknown message during authentication: "
 275                             "type %d", type);
 276                         goto skip;
 277                 }
 278
 279                 if (!*(meth->enabled)) {
 280                         verbose("%s authentication disabled.", meth->name);
 281                         goto skip;
 282                 }
 283
 284                 authenticated = meth->method(authctxt, info, sizeof(info));
 285                 if (authenticated == -1)
 286                         continue; /* "postponed" */
 287
 288 #ifdef BSD_AUTH
 289                 if (authctxt->as) {
 290                         auth_close(authctxt->as);
 291                         authctxt->as = NULL;
 292                 }
 293 #endif
 294                 if (!authctxt->valid && authenticated)
 295                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 296                             authctxt->user);
 297
 298 #ifdef _UNICOS
 299                 if (authenticated && cray_access_denied(authctxt->user)) {
 300                         authenticated = 0;
 301                         fatal("Access denied for user %s.",authctxt->user);
 302                 }
 303 #endif /* _UNICOS */
 304
 305 #ifdef HAVE_CYGWIN
 306                 if (authenticated &&
 307                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
 308                     authctxt->pw)) {
 309                         packet_disconnect("Authentication rejected for uid %d.",
 310                             authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
 311                         authenticated = 0;
 312                 }
 313 #else
 314                 /* Special handling for root */
 315                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 316                     !auth_root_allowed(meth->name)) {
 317                         authenticated = 0;
 318 # ifdef SSH_AUDIT_EVENTS
 319                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 320 # endif
 321                 }
 322 #endif
 323
 324 #ifdef USE_PAM
 325                 if (options.use_pam && authenticated &&
 326                     !PRIVSEP(do_pam_account())) {
 327                         char *msg;
 328                         size_t len;
 329
 330                         error("Access denied for user %s by PAM account "
 331                             "configuration", authctxt->user);
 332                         len = buffer_len(&loginmsg);
 333                         buffer_append(&loginmsg, "\0", 1);
 334                         msg = buffer_ptr(&loginmsg);
 335                         /* strip trailing newlines */
 336                         if (len > 0)
 337                                 while (len > 0 && msg[--len] == '\n')
 338                                         msg[len] = '\0';
 339                         else
 340                                 msg = "Access denied.";
 341                         packet_disconnect(msg);
 342                 }
 343 #endif
 344
 345  skip:
 346                 /* Log before sending the reply */
 347                 auth_log(authctxt, authenticated, get_authname(type), info);
 348
 349                 if (client_user != NULL) {
 350                         xfree(client_user);
 351                         client_user = NULL;
 352                 }
 353
 354                 if (authenticated)
 355                         return;
 356
 357                 if (authctxt->failures++ > options.max_authtries) {
 358 #ifdef SSH_AUDIT_EVENTS
 359                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 360 #endif
 361                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 362                 }
 363
 364                 packet_start(SSH_SMSG_FAILURE);
 365                 packet_send();
 366                 packet_write_wait();
 367         }
 368 }
 369
 370 /*
 371  * Performs authentication of an incoming connection.  Session key has already
 372  * been exchanged and encryption is enabled.
 373  */
 374 void
 375 do_authentication(Authctxt *authctxt)
 376 {
 377         u_int ulen;
 378         char *user, *style = NULL;
 379
 380         /* Get the name of the user that we wish to log in as. */
 381         packet_read_expect(SSH_CMSG_USER);
 382
 383         /* Get the user name. */
 384         user = packet_get_string(&ulen);
 385         packet_check_eom();
 386
 387         if ((style = strchr(user, ':')) != NULL)
 388                 *style++ = '\0';
 389
 390         authctxt->user = user;
 391         authctxt->style = style;
 392
 393         /* Verify that the user is a valid user. */
 394         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 395                 authctxt->valid = 1;
 396         else {
 397                 debug("do_authentication: invalid user %s", user);
 398                 authctxt->pw = fakepw();
 399         }
 400
 401         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 402             use_privsep ? " [net]" : "");
 403
 404 #ifdef USE_PAM
 405         if (options.use_pam)
 406                 PRIVSEP(start_pam(authctxt));
 407 #endif
 408
 409         /*
 410          * If we are not running as root, the user must have the same uid as
 411          * the server.
 412          */
 413 #ifndef HAVE_CYGWIN
 414         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 415             authctxt->pw->pw_uid != getuid())
 416                 packet_disconnect("Cannot change user when server not running as root.");
 417 #endif
 418
 419         /*
 420          * Loop until the user has been authenticated or the connection is
 421          * closed, do_authloop() returns only if authentication is successful
 422          */
 423         do_authloop(authctxt);
 424
 425         /* The user has been authenticated and accepted. */
 426         packet_start(SSH_SMSG_SUCCESS);
 427         packet_send();
 428         packet_write_wait();
 429 }