auth2.c

   1 /* $OpenBSD: auth2.c,v 1.112 2006/07/22 20:48:22 stevesk 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 <string.h>
  32
  33 #include "ssh2.h"
  34 #include "xmalloc.h"
  35 #include "packet.h"
  36 #include "log.h"
  37 #include "servconf.h"
  38 #include "compat.h"
  39 #include "auth.h"
  40 #include "dispatch.h"
  41 #include "pathnames.h"
  42 #include "monitor_wrap.h"
  43 #include "buffer.h"
  44
  45 #ifdef GSSAPI
  46 #include "ssh-gss.h"
  47 #endif
  48
  49 /* import */
  50 extern ServerOptions options;
  51 extern u_char *session_id2;
  52 extern u_int session_id2_len;
  53 extern Buffer loginmsg;
  54
  55 /* methods */
  56
  57 extern Authmethod method_none;
  58 extern Authmethod method_pubkey;
  59 extern Authmethod method_passwd;
  60 extern Authmethod method_kbdint;
  61 extern Authmethod method_hostbased;
  62 #ifdef GSSAPI
  63 extern Authmethod method_gssapi;
  64 #endif
  65
  66 Authmethod *authmethods[] = {
  67         &method_none,
  68         &method_pubkey,
  69 #ifdef GSSAPI
  70         &method_gssapi,
  71 #endif
  72         &method_passwd,
  73         &method_kbdint,
  74         &method_hostbased,
  75         NULL
  76 };
  77
  78 /* protocol */
  79
  80 static void input_service_request(int, u_int32_t, void *);
  81 static void input_userauth_request(int, u_int32_t, void *);
  82
  83 /* helper */
  84 static Authmethod *authmethod_lookup(const char *);
  85 static char *authmethods_get(void);
  86 int user_key_allowed(struct passwd *, Key *);
  87
  88 /*
  89  * loop until authctxt->success == TRUE
  90  */
  91
  92 void
  93 do_authentication2(Authctxt *authctxt)
  94 {
  95         /* challenge-response is implemented via keyboard interactive */
  96         if (options.challenge_response_authentication)
  97                 options.kbd_interactive_authentication = 1;
  98
  99         dispatch_init(&dispatch_protocol_error);
 100         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 101         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 102 }
 103
 104 /*ARGSUSED*/
 105 static void
 106 input_service_request(int type, u_int32_t seq, void *ctxt)
 107 {
 108         Authctxt *authctxt = ctxt;
 109         u_int len;
 110         int acceptit = 0;
 111         char *service = packet_get_string(&len);
 112         packet_check_eom();
 113
 114         if (authctxt == NULL)
 115                 fatal("input_service_request: no authctxt");
 116
 117         if (strcmp(service, "ssh-userauth") == 0) {
 118                 if (!authctxt->success) {
 119                         acceptit = 1;
 120                         /* now we can handle user-auth requests */
 121                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 122                 }
 123         }
 124         /* XXX all other service requests are denied */
 125
 126         if (acceptit) {
 127                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 128                 packet_put_cstring(service);
 129                 packet_send();
 130                 packet_write_wait();
 131         } else {
 132                 debug("bad service request %s", service);
 133                 packet_disconnect("bad service request %s", service);
 134         }
 135         xfree(service);
 136 }
 137
 138 /*ARGSUSED*/
 139 static void
 140 input_userauth_request(int type, u_int32_t seq, void *ctxt)
 141 {
 142         Authctxt *authctxt = ctxt;
 143         Authmethod *m = NULL;
 144         char *user, *service, *method, *style = NULL;
 145         int authenticated = 0;
 146
 147         if (authctxt == NULL)
 148                 fatal("input_userauth_request: no authctxt");
 149
 150         user = packet_get_string(NULL);
 151         service = packet_get_string(NULL);
 152         method = packet_get_string(NULL);
 153         debug("userauth-request for user %s service %s method %s", user, service, method);
 154         debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
 155
 156         if ((style = strchr(user, ':')) != NULL)
 157                 *style++ = 0;
 158
 159         if (authctxt->attempt++ == 0) {
 160                 /* setup auth context */
 161                 authctxt->pw = PRIVSEP(getpwnamallow(user));
 162                 authctxt->user = xstrdup(user);
 163                 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
 164                         authctxt->valid = 1;
 165                         debug2("input_userauth_request: setting up authctxt for %s", user);
 166                 } else {
 167                         logit("input_userauth_request: invalid user %s", user);
 168                         authctxt->pw = fakepw();
 169 #ifdef SSH_AUDIT_EVENTS
 170                         PRIVSEP(audit_event(SSH_INVALID_USER));
 171 #endif
 172                 }
 173 #ifdef USE_PAM
 174                 if (options.use_pam)
 175                         PRIVSEP(start_pam(authctxt));
 176 #endif
 177                 setproctitle("%s%s", authctxt->valid ? user : "unknown",
 178                     use_privsep ? " [net]" : "");
 179                 authctxt->service = xstrdup(service);
 180                 authctxt->style = style ? xstrdup(style) : NULL;
 181                 if (use_privsep)
 182                         mm_inform_authserv(service, style);
 183         } else if (strcmp(user, authctxt->user) != 0 ||
 184             strcmp(service, authctxt->service) != 0) {
 185                 packet_disconnect("Change of username or service not allowed: "
 186                     "(%s,%s) -> (%s,%s)",
 187                     authctxt->user, authctxt->service, user, service);
 188         }
 189         /* reset state */
 190         auth2_challenge_stop(authctxt);
 191
 192 #ifdef GSSAPI
 193         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 194         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 195 #endif
 196
 197         authctxt->postponed = 0;
 198
 199         /* try to authenticate user */
 200         m = authmethod_lookup(method);
 201         if (m != NULL) {
 202                 debug2("input_userauth_request: try method %s", method);
 203                 authenticated = m->userauth(authctxt);
 204         }
 205         userauth_finish(authctxt, authenticated, method);
 206
 207         xfree(service);
 208         xfree(user);
 209         xfree(method);
 210 }
 211
 212 void
 213 userauth_finish(Authctxt *authctxt, int authenticated, char *method)
 214 {
 215         char *methods;
 216
 217         if (!authctxt->valid && authenticated)
 218                 fatal("INTERNAL ERROR: authenticated invalid user %s",
 219                     authctxt->user);
 220
 221         /* Special handling for root */
 222         if (authenticated && authctxt->pw->pw_uid == 0 &&
 223             !auth_root_allowed(method)) {
 224                 authenticated = 0;
 225 #ifdef SSH_AUDIT_EVENTS
 226                 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 227 #endif
 228         }
 229
 230 #ifdef USE_PAM
 231         if (options.use_pam && authenticated) {
 232                 if (!PRIVSEP(do_pam_account())) {
 233                         /* if PAM returned a message, send it to the user */
 234                         if (buffer_len(&loginmsg) > 0) {
 235                                 buffer_append(&loginmsg, "\0", 1);
 236                                 userauth_send_banner(buffer_ptr(&loginmsg));
 237                                 packet_write_wait();
 238                         }
 239                         fatal("Access denied for user %s by PAM account "
 240                             "configuration", authctxt->user);
 241                 }
 242         }
 243 #endif
 244
 245 #ifdef _UNICOS
 246         if (authenticated && cray_access_denied(authctxt->user)) {
 247                 authenticated = 0;
 248                 fatal("Access denied for user %s.",authctxt->user);
 249         }
 250 #endif /* _UNICOS */
 251
 252         /* Log before sending the reply */
 253         auth_log(authctxt, authenticated, method, " ssh2");
 254
 255         if (authctxt->postponed)
 256                 return;
 257
 258         /* XXX todo: check if multiple auth methods are needed */
 259         if (authenticated == 1) {
 260                 /* turn off userauth */
 261                 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
 262                 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
 263                 packet_send();
 264                 packet_write_wait();
 265                 /* now we can break out */
 266                 authctxt->success = 1;
 267         } else {
 268                 if (authctxt->failures++ > options.max_authtries) {
 269 #ifdef SSH_AUDIT_EVENTS
 270                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 271 #endif
 272                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 273                 }
 274                 methods = authmethods_get();
 275                 packet_start(SSH2_MSG_USERAUTH_FAILURE);
 276                 packet_put_cstring(methods);
 277                 packet_put_char(0);     /* XXX partial success, unused */
 278                 packet_send();
 279                 packet_write_wait();
 280                 xfree(methods);
 281         }
 282 }
 283
 284 #define DELIM   ","
 285
 286 static char *
 287 authmethods_get(void)
 288 {
 289         Buffer b;
 290         char *list;
 291         int i;
 292
 293         buffer_init(&b);
 294         for (i = 0; authmethods[i] != NULL; i++) {
 295                 if (strcmp(authmethods[i]->name, "none") == 0)
 296                         continue;
 297                 if (authmethods[i]->enabled != NULL &&
 298                     *(authmethods[i]->enabled) != 0) {
 299                         if (buffer_len(&b) > 0)
 300                                 buffer_append(&b, ",", 1);
 301                         buffer_append(&b, authmethods[i]->name,
 302                             strlen(authmethods[i]->name));
 303                 }
 304         }
 305         buffer_append(&b, "\0", 1);
 306         list = xstrdup(buffer_ptr(&b));
 307         buffer_free(&b);
 308         return list;
 309 }
 310
 311 static Authmethod *
 312 authmethod_lookup(const char *name)
 313 {
 314         int i;
 315
 316         if (name != NULL)
 317                 for (i = 0; authmethods[i] != NULL; i++)
 318                         if (authmethods[i]->enabled != NULL &&
 319                             *(authmethods[i]->enabled) != 0 &&
 320                             strcmp(name, authmethods[i]->name) == 0)
 321                                 return authmethods[i];
 322         debug2("Unrecognized authentication method name: %s",
 323             name ? name : "NULL");
 324         return NULL;
 325 }