auth2.c

   1 /* $OpenBSD: auth2.c,v 1.113 2006/08/03 03:34:41 deraadt 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
  30 #include <pwd.h>
  31 #include <stdarg.h>
  32 #include <string.h>
  33
  34 #include "xmalloc.h"
  35 #include "ssh2.h"
  36 #include "packet.h"
  37 #include "log.h"
  38 #include "buffer.h"
  39 #include "servconf.h"
  40 #include "compat.h"
  41 #include "key.h"
  42 #include "hostfile.h"
  43 #include "auth.h"
  44 #include "dispatch.h"
  45 #include "pathnames.h"
  46 #include "buffer.h"
  47
  48 #ifdef GSSAPI
  49 #include "ssh-gss.h"
  50 #endif
  51 #include "monitor_wrap.h"
  52
  53 /* import */
  54 extern ServerOptions options;
  55 extern u_char *session_id2;
  56 extern u_int session_id2_len;
  57 extern Buffer loginmsg;
  58
  59 /* methods */
  60
  61 extern Authmethod method_none;
  62 extern Authmethod method_pubkey;
  63 extern Authmethod method_passwd;
  64 extern Authmethod method_kbdint;
  65 extern Authmethod method_hostbased;
  66 #ifdef GSSAPI
  67 extern Authmethod method_gssapi;
  68 #endif
  69
  70 Authmethod *authmethods[] = {
  71         &method_none,
  72         &method_pubkey,
  73 #ifdef GSSAPI
  74         &method_gssapi,
  75 #endif
  76         &method_passwd,
  77         &method_kbdint,
  78         &method_hostbased,
  79         NULL
  80 };
  81
  82 /* protocol */
  83
  84 static void input_service_request(int, u_int32_t, void *);
  85 static void input_userauth_request(int, u_int32_t, void *);
  86
  87 /* helper */
  88 static Authmethod *authmethod_lookup(const char *);
  89 static char *authmethods_get(void);
  90 int user_key_allowed(struct passwd *, Key *);
  91
  92 /*
  93  * loop until authctxt->success == TRUE
  94  */
  95
  96 void
  97 do_authentication2(Authctxt *authctxt)
  98 {
  99         /* challenge-response is implemented via keyboard interactive */
 100         if (options.challenge_response_authentication)
 101                 options.kbd_interactive_authentication = 1;
 102
 103         dispatch_init(&dispatch_protocol_error);
 104         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 105         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 106 }
 107
 108 /*ARGSUSED*/
 109 static void
 110 input_service_request(int type, u_int32_t seq, void *ctxt)
 111 {
 112         Authctxt *authctxt = ctxt;
 113         u_int len;
 114         int acceptit = 0;
 115         char *service = packet_get_string(&len);
 116         packet_check_eom();
 117
 118         if (authctxt == NULL)
 119                 fatal("input_service_request: no authctxt");
 120
 121         if (strcmp(service, "ssh-userauth") == 0) {
 122                 if (!authctxt->success) {
 123                         acceptit = 1;
 124                         /* now we can handle user-auth requests */
 125                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 126                 }
 127         }
 128         /* XXX all other service requests are denied */
 129
 130         if (acceptit) {
 131                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 132                 packet_put_cstring(service);
 133                 packet_send();
 134                 packet_write_wait();
 135         } else {
 136                 debug("bad service request %s", service);
 137                 packet_disconnect("bad service request %s", service);
 138         }
 139         xfree(service);
 140 }
 141
 142 /*ARGSUSED*/
 143 static void
 144 input_userauth_request(int type, u_int32_t seq, void *ctxt)
 145 {
 146         Authctxt *authctxt = ctxt;
 147         Authmethod *m = NULL;
 148         char *user, *service, *method, *style = NULL;
 149         int authenticated = 0;
 150
 151         if (authctxt == NULL)
 152                 fatal("input_userauth_request: no authctxt");
 153
 154         user = packet_get_string(NULL);
 155         service = packet_get_string(NULL);
 156         method = packet_get_string(NULL);
 157         debug("userauth-request for user %s service %s method %s", user, service, method);
 158         debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
 159
 160         if ((style = strchr(user, ':')) != NULL)
 161                 *style++ = 0;
 162
 163         if (authctxt->attempt++ == 0) {
 164                 /* setup auth context */
 165                 authctxt->pw = PRIVSEP(getpwnamallow(user));
 166                 authctxt->user = xstrdup(user);
 167                 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
 168                         authctxt->valid = 1;
 169                         debug2("input_userauth_request: setting up authctxt for %s", user);
 170                 } else {
 171                         logit("input_userauth_request: invalid user %s", user);
 172                         authctxt->pw = fakepw();
 173 #ifdef SSH_AUDIT_EVENTS
 174                         PRIVSEP(audit_event(SSH_INVALID_USER));
 175 #endif
 176                 }
 177 #ifdef USE_PAM
 178                 if (options.use_pam)
 179                         PRIVSEP(start_pam(authctxt));
 180 #endif
 181                 setproctitle("%s%s", authctxt->valid ? user : "unknown",
 182                     use_privsep ? " [net]" : "");
 183                 authctxt->service = xstrdup(service);
 184                 authctxt->style = style ? xstrdup(style) : NULL;
 185                 if (use_privsep)
 186                         mm_inform_authserv(service, style);
 187         } else if (strcmp(user, authctxt->user) != 0 ||
 188             strcmp(service, authctxt->service) != 0) {
 189                 packet_disconnect("Change of username or service not allowed: "
 190                     "(%s,%s) -> (%s,%s)",
 191                     authctxt->user, authctxt->service, user, service);
 192         }
 193         /* reset state */
 194         auth2_challenge_stop(authctxt);
 195
 196 #ifdef GSSAPI
 197         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 198         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 199 #endif
 200
 201         authctxt->postponed = 0;
 202
 203         /* try to authenticate user */
 204         m = authmethod_lookup(method);
 205         if (m != NULL) {
 206                 debug2("input_userauth_request: try method %s", method);
 207                 authenticated = m->userauth(authctxt);
 208         }
 209         userauth_finish(authctxt, authenticated, method);
 210
 211         xfree(service);
 212         xfree(user);
 213         xfree(method);
 214 }
 215
 216 void
 217 userauth_finish(Authctxt *authctxt, int authenticated, char *method)
 218 {
 219         char *methods;
 220
 221         if (!authctxt->valid && authenticated)
 222                 fatal("INTERNAL ERROR: authenticated invalid user %s",
 223                     authctxt->user);
 224
 225         /* Special handling for root */
 226         if (authenticated && authctxt->pw->pw_uid == 0 &&
 227             !auth_root_allowed(method)) {
 228                 authenticated = 0;
 229 #ifdef SSH_AUDIT_EVENTS
 230                 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 231 #endif
 232         }
 233
 234 #ifdef USE_PAM
 235         if (options.use_pam && authenticated) {
 236                 if (!PRIVSEP(do_pam_account())) {
 237                         /* if PAM returned a message, send it to the user */
 238                         if (buffer_len(&loginmsg) > 0) {
 239                                 buffer_append(&loginmsg, "\0", 1);
 240                                 userauth_send_banner(buffer_ptr(&loginmsg));
 241                                 packet_write_wait();
 242                         }
 243                         fatal("Access denied for user %s by PAM account "
 244                             "configuration", authctxt->user);
 245                 }
 246         }
 247 #endif
 248
 249 #ifdef _UNICOS
 250         if (authenticated && cray_access_denied(authctxt->user)) {
 251                 authenticated = 0;
 252                 fatal("Access denied for user %s.",authctxt->user);
 253         }
 254 #endif /* _UNICOS */
 255
 256         /* Log before sending the reply */
 257         auth_log(authctxt, authenticated, method, " ssh2");
 258
 259         if (authctxt->postponed)
 260                 return;
 261
 262         /* XXX todo: check if multiple auth methods are needed */
 263         if (authenticated == 1) {
 264                 /* turn off userauth */
 265                 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
 266                 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
 267                 packet_send();
 268                 packet_write_wait();
 269                 /* now we can break out */
 270                 authctxt->success = 1;
 271         } else {
 272                 if (authctxt->failures++ > options.max_authtries) {
 273 #ifdef SSH_AUDIT_EVENTS
 274                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 275 #endif
 276                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 277                 }
 278                 methods = authmethods_get();
 279                 packet_start(SSH2_MSG_USERAUTH_FAILURE);
 280                 packet_put_cstring(methods);
 281                 packet_put_char(0);     /* XXX partial success, unused */
 282                 packet_send();
 283                 packet_write_wait();
 284                 xfree(methods);
 285         }
 286 }
 287
 288 #define DELIM   ","
 289
 290 static char *
 291 authmethods_get(void)
 292 {
 293         Buffer b;
 294         char *list;
 295         int i;
 296
 297         buffer_init(&b);
 298         for (i = 0; authmethods[i] != NULL; i++) {
 299                 if (strcmp(authmethods[i]->name, "none") == 0)
 300                         continue;
 301                 if (authmethods[i]->enabled != NULL &&
 302                     *(authmethods[i]->enabled) != 0) {
 303                         if (buffer_len(&b) > 0)
 304                                 buffer_append(&b, ",", 1);
 305                         buffer_append(&b, authmethods[i]->name,
 306                             strlen(authmethods[i]->name));
 307                 }
 308         }
 309         buffer_append(&b, "\0", 1);
 310         list = xstrdup(buffer_ptr(&b));
 311         buffer_free(&b);
 312         return list;
 313 }
 314
 315 static Authmethod *
 316 authmethod_lookup(const char *name)
 317 {
 318         int i;
 319
 320         if (name != NULL)
 321                 for (i = 0; authmethods[i] != NULL; i++)
 322                         if (authmethods[i]->enabled != NULL &&
 323                             *(authmethods[i]->enabled) != 0 &&
 324                             strcmp(name, authmethods[i]->name) == 0)
 325                                 return authmethods[i];
 326         debug2("Unrecognized authentication method name: %s",
 327             name ? name : "NULL");
 328         return NULL;
 329 }