auth2.c

   1 /* $OpenBSD: auth2.c,v 1.121 2009/06/22 05:39:28 dtucker 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 #include <sys/uio.h>
  31
  32 #include <fcntl.h>
  33 #include <pwd.h>
  34 #include <stdarg.h>
  35 #include <string.h>
  36 #include <unistd.h>
  37
  38 #include "atomicio.h"
  39 #include "xmalloc.h"
  40 #include "ssh2.h"
  41 #include "packet.h"
  42 #include "log.h"
  43 #include "buffer.h"
  44 #include "servconf.h"
  45 #include "compat.h"
  46 #include "key.h"
  47 #include "hostfile.h"
  48 #include "auth.h"
  49 #include "dispatch.h"
  50 #include "pathnames.h"
  51 #include "buffer.h"
  52
  53 #ifdef GSSAPI
  54 #include "ssh-gss.h"
  55 #endif
  56 #include "monitor_wrap.h"
  57
  58 /* import */
  59 extern ServerOptions options;
  60 extern u_char *session_id2;
  61 extern u_int session_id2_len;
  62 extern Buffer loginmsg;
  63
  64 /* methods */
  65
  66 extern Authmethod method_none;
  67 extern Authmethod method_pubkey;
  68 extern Authmethod method_passwd;
  69 extern Authmethod method_kbdint;
  70 extern Authmethod method_hostbased;
  71 #ifdef GSSAPI
  72 extern Authmethod method_gssapi;
  73 #endif
  74 #ifdef JPAKE
  75 extern Authmethod method_jpake;
  76 #endif
  77
  78 Authmethod *authmethods[] = {
  79         &method_none,
  80         &method_pubkey,
  81 #ifdef GSSAPI
  82         &method_gssapi,
  83 #endif
  84 #ifdef JPAKE
  85         &method_jpake,
  86 #endif
  87         &method_passwd,
  88         &method_kbdint,
  89         &method_hostbased,
  90         NULL
  91 };
  92
  93 /* protocol */
  94
  95 static void input_service_request(int, u_int32_t, void *);
  96 static void input_userauth_request(int, u_int32_t, void *);
  97
  98 /* helper */
  99 static Authmethod *authmethod_lookup(const char *);
 100 static char *authmethods_get(void);
 101
 102 char *
 103 auth2_read_banner(void)
 104 {
 105         struct stat st;
 106         char *banner = NULL;
 107         size_t len, n;
 108         int fd;
 109
 110         if ((fd = open(options.banner, O_RDONLY)) == -1)
 111                 return (NULL);
 112         if (fstat(fd, &st) == -1) {
 113                 close(fd);
 114                 return (NULL);
 115         }
 116         if (st.st_size > 1*1024*1024) {
 117                 close(fd);
 118                 return (NULL);
 119         }
 120
 121         len = (size_t)st.st_size;               /* truncate */
 122         banner = xmalloc(len + 1);
 123         n = atomicio(read, fd, banner, len);
 124         close(fd);
 125
 126         if (n != len) {
 127                 xfree(banner);
 128                 return (NULL);
 129         }
 130         banner[n] = '\0';
 131
 132         return (banner);
 133 }
 134
 135 void
 136 userauth_send_banner(const char *msg)
 137 {
 138         if (datafellows & SSH_BUG_BANNER)
 139                 return;
 140
 141         packet_start(SSH2_MSG_USERAUTH_BANNER);
 142         packet_put_cstring(msg);
 143         packet_put_cstring("");         /* language, unused */
 144         packet_send();
 145         debug("%s: sent", __func__);
 146 }
 147
 148 static void
 149 userauth_banner(void)
 150 {
 151         char *banner = NULL;
 152
 153         if (options.banner == NULL ||
 154             strcasecmp(options.banner, "none") == 0 ||
 155             (datafellows & SSH_BUG_BANNER) != 0)
 156                 return;
 157
 158         if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
 159                 goto done;
 160         userauth_send_banner(banner);
 161
 162 done:
 163         if (banner)
 164                 xfree(banner);
 165 }
 166
 167 /*
 168  * loop until authctxt->success == TRUE
 169  */
 170 void
 171 do_authentication2(Authctxt *authctxt)
 172 {
 173         dispatch_init(&dispatch_protocol_error);
 174         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 175         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 176 }
 177
 178 /*ARGSUSED*/
 179 static void
 180 input_service_request(int type, u_int32_t seq, void *ctxt)
 181 {
 182         Authctxt *authctxt = ctxt;
 183         u_int len;
 184         int acceptit = 0;
 185         char *service = packet_get_string(&len);
 186         packet_check_eom();
 187
 188         if (authctxt == NULL)
 189                 fatal("input_service_request: no authctxt");
 190
 191         if (strcmp(service, "ssh-userauth") == 0) {
 192                 if (!authctxt->success) {
 193                         acceptit = 1;
 194                         /* now we can handle user-auth requests */
 195                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 196                 }
 197         }
 198         /* XXX all other service requests are denied */
 199
 200         if (acceptit) {
 201                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 202                 packet_put_cstring(service);
 203                 packet_send();
 204                 packet_write_wait();
 205         } else {
 206                 debug("bad service request %s", service);
 207                 packet_disconnect("bad service request %s", service);
 208         }
 209         xfree(service);
 210 }
 211
 212 /*ARGSUSED*/
 213 static void
 214 input_userauth_request(int type, u_int32_t seq, void *ctxt)
 215 {
 216         Authctxt *authctxt = ctxt;
 217         Authmethod *m = NULL;
 218         char *user, *service, *method, *style = NULL;
 219         int authenticated = 0;
 220
 221         if (authctxt == NULL)
 222                 fatal("input_userauth_request: no authctxt");
 223
 224         user = packet_get_string(NULL);
 225         service = packet_get_string(NULL);
 226         method = packet_get_string(NULL);
 227         debug("userauth-request for user %s service %s method %s", user, service, method);
 228         debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
 229
 230         if ((style = strchr(user, ':')) != NULL)
 231                 *style++ = 0;
 232
 233         if (authctxt->attempt++ == 0) {
 234                 /* setup auth context */
 235                 authctxt->pw = PRIVSEP(getpwnamallow(user));
 236                 authctxt->user = xstrdup(user);
 237                 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
 238                         authctxt->valid = 1;
 239                         debug2("input_userauth_request: setting up authctxt for %s", user);
 240                 } else {
 241                         logit("input_userauth_request: invalid user %s", user);
 242                         authctxt->pw = fakepw();
 243 #ifdef SSH_AUDIT_EVENTS
 244                         PRIVSEP(audit_event(SSH_INVALID_USER));
 245 #endif
 246                 }
 247 #ifdef USE_PAM
 248                 if (options.use_pam)
 249                         PRIVSEP(start_pam(authctxt));
 250 #endif
 251                 setproctitle("%s%s", authctxt->valid ? user : "unknown",
 252                     use_privsep ? " [net]" : "");
 253                 authctxt->service = xstrdup(service);
 254                 authctxt->style = style ? xstrdup(style) : NULL;
 255                 if (use_privsep)
 256                         mm_inform_authserv(service, style);
 257                 userauth_banner();
 258         } else if (strcmp(user, authctxt->user) != 0 ||
 259             strcmp(service, authctxt->service) != 0) {
 260                 packet_disconnect("Change of username or service not allowed: "
 261                     "(%s,%s) -> (%s,%s)",
 262                     authctxt->user, authctxt->service, user, service);
 263         }
 264         /* reset state */
 265         auth2_challenge_stop(authctxt);
 266 #ifdef JPAKE
 267         auth2_jpake_stop(authctxt);
 268 #endif
 269
 270 #ifdef GSSAPI
 271         /* XXX move to auth2_gssapi_stop() */
 272         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 273         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 274 #endif
 275
 276         authctxt->postponed = 0;
 277
 278         /* try to authenticate user */
 279         m = authmethod_lookup(method);
 280         if (m != NULL && authctxt->failures < options.max_authtries) {
 281                 debug2("input_userauth_request: try method %s", method);
 282                 authenticated = m->userauth(authctxt);
 283         }
 284         userauth_finish(authctxt, authenticated, method);
 285
 286         xfree(service);
 287         xfree(user);
 288         xfree(method);
 289 }
 290
 291 void
 292 userauth_finish(Authctxt *authctxt, int authenticated, char *method)
 293 {
 294         char *methods;
 295
 296         if (!authctxt->valid && authenticated)
 297                 fatal("INTERNAL ERROR: authenticated invalid user %s",
 298                     authctxt->user);
 299
 300         /* Special handling for root */
 301         if (authenticated && authctxt->pw->pw_uid == 0 &&
 302             !auth_root_allowed(method)) {
 303                 authenticated = 0;
 304 #ifdef SSH_AUDIT_EVENTS
 305                 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 306 #endif
 307         }
 308
 309 #ifdef USE_PAM
 310         if (options.use_pam && authenticated) {
 311                 if (!PRIVSEP(do_pam_account())) {
 312                         /* if PAM returned a message, send it to the user */
 313                         if (buffer_len(&loginmsg) > 0) {
 314                                 buffer_append(&loginmsg, "\0", 1);
 315                                 userauth_send_banner(buffer_ptr(&loginmsg));
 316                                 packet_write_wait();
 317                         }
 318                         fatal("Access denied for user %s by PAM account "
 319                             "configuration", authctxt->user);
 320                 }
 321         }
 322 #endif
 323
 324 #ifdef _UNICOS
 325         if (authenticated && cray_access_denied(authctxt->user)) {
 326                 authenticated = 0;
 327                 fatal("Access denied for user %s.",authctxt->user);
 328         }
 329 #endif /* _UNICOS */
 330
 331         /* Log before sending the reply */
 332         auth_log(authctxt, authenticated, method, " ssh2");
 333
 334         if (authctxt->postponed)
 335                 return;
 336
 337         /* XXX todo: check if multiple auth methods are needed */
 338         if (authenticated == 1) {
 339                 /* turn off userauth */
 340                 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
 341                 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
 342                 packet_send();
 343                 packet_write_wait();
 344                 /* now we can break out */
 345                 authctxt->success = 1;
 346         } else {
 347
 348                 /* Allow initial try of "none" auth without failure penalty */
 349                 if (authctxt->attempt > 1 || strcmp(method, "none") != 0)
 350                         authctxt->failures++;
 351                 if (authctxt->failures >= options.max_authtries) {
 352 #ifdef SSH_AUDIT_EVENTS
 353                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 354 #endif
 355                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 356                 }
 357                 methods = authmethods_get();
 358                 packet_start(SSH2_MSG_USERAUTH_FAILURE);
 359                 packet_put_cstring(methods);
 360                 packet_put_char(0);     /* XXX partial success, unused */
 361                 packet_send();
 362                 packet_write_wait();
 363                 xfree(methods);
 364         }
 365 }
 366
 367 static char *
 368 authmethods_get(void)
 369 {
 370         Buffer b;
 371         char *list;
 372         int i;
 373
 374         buffer_init(&b);
 375         for (i = 0; authmethods[i] != NULL; i++) {
 376                 if (strcmp(authmethods[i]->name, "none") == 0)
 377                         continue;
 378                 if (authmethods[i]->enabled != NULL &&
 379                     *(authmethods[i]->enabled) != 0) {
 380                         if (buffer_len(&b) > 0)
 381                                 buffer_append(&b, ",", 1);
 382                         buffer_append(&b, authmethods[i]->name,
 383                             strlen(authmethods[i]->name));
 384                 }
 385         }
 386         buffer_append(&b, "\0", 1);
 387         list = xstrdup(buffer_ptr(&b));
 388         buffer_free(&b);
 389         return list;
 390 }
 391
 392 static Authmethod *
 393 authmethod_lookup(const char *name)
 394 {
 395         int i;
 396
 397         if (name != NULL)
 398                 for (i = 0; authmethods[i] != NULL; i++)
 399                         if (authmethods[i]->enabled != NULL &&
 400                             *(authmethods[i]->enabled) != 0 &&
 401                             strcmp(name, authmethods[i]->name) == 0)
 402                                 return authmethods[i];
 403         debug2("Unrecognized authentication method name: %s",
 404             name ? name : "NULL");
 405         return NULL;
 406 }
 407