auth2.c

   1 /* $OpenBSD: auth2.c,v 1.111 2006/07/06 16:03:53 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
  32 #include "ssh2.h"
  33 #include "xmalloc.h"
  34 #include "packet.h"
  35 #include "log.h"
  36 #include "servconf.h"
  37 #include "compat.h"
  38 #include "auth.h"
  39 #include "dispatch.h"
  40 #include "pathnames.h"
  41 #include "monitor_wrap.h"
  42 #include "buffer.h"
  43
  44 #ifdef GSSAPI
  45 #include "ssh-gss.h"
  46 #endif
  47
  48 /* import */
  49 extern ServerOptions options;
  50 extern u_char *session_id2;
  51 extern u_int session_id2_len;
  52 extern Buffer loginmsg;
  53
  54 /* methods */
  55
  56 extern Authmethod method_none;
  57 extern Authmethod method_pubkey;
  58 extern Authmethod method_passwd;
  59 extern Authmethod method_kbdint;
  60 extern Authmethod method_hostbased;
  61 #ifdef GSSAPI
  62 extern Authmethod method_gssapi;
  63 #endif
  64
  65 Authmethod *authmethods[] = {
  66         &method_none,
  67         &method_pubkey,
  68 #ifdef GSSAPI
  69         &method_gssapi,
  70 #endif
  71         &method_passwd,
  72         &method_kbdint,
  73         &method_hostbased,
  74         NULL
  75 };
  76
  77 /* protocol */
  78
  79 static void input_service_request(int, u_int32_t, void *);
  80 static void input_userauth_request(int, u_int32_t, void *);
  81
  82 /* helper */
  83 static Authmethod *authmethod_lookup(const char *);
  84 static char *authmethods_get(void);
  85 int user_key_allowed(struct passwd *, Key *);
  86
  87 /*
  88  * loop until authctxt->success == TRUE
  89  */
  90
  91 void
  92 do_authentication2(Authctxt *authctxt)
  93 {
  94         /* challenge-response is implemented via keyboard interactive */
  95         if (options.challenge_response_authentication)
  96                 options.kbd_interactive_authentication = 1;
  97
  98         dispatch_init(&dispatch_protocol_error);
  99         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 100         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 101 }
 102
 103 /*ARGSUSED*/
 104 static void
 105 input_service_request(int type, u_int32_t seq, void *ctxt)
 106 {
 107         Authctxt *authctxt = ctxt;
 108         u_int len;
 109         int acceptit = 0;
 110         char *service = packet_get_string(&len);
 111         packet_check_eom();
 112
 113         if (authctxt == NULL)
 114                 fatal("input_service_request: no authctxt");
 115
 116         if (strcmp(service, "ssh-userauth") == 0) {
 117                 if (!authctxt->success) {
 118                         acceptit = 1;
 119                         /* now we can handle user-auth requests */
 120                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 121                 }
 122         }
 123         /* XXX all other service requests are denied */
 124
 125         if (acceptit) {
 126                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 127                 packet_put_cstring(service);
 128                 packet_send();
 129                 packet_write_wait();
 130         } else {
 131                 debug("bad service request %s", service);
 132                 packet_disconnect("bad service request %s", service);
 133         }
 134         xfree(service);
 135 }
 136
 137 /*ARGSUSED*/
 138 static void
 139 input_userauth_request(int type, u_int32_t seq, void *ctxt)
 140 {
 141         Authctxt *authctxt = ctxt;
 142         Authmethod *m = NULL;
 143         char *user, *service, *method, *style = NULL;
 144         int authenticated = 0;
 145
 146         if (authctxt == NULL)
 147                 fatal("input_userauth_request: no authctxt");
 148
 149         user = packet_get_string(NULL);
 150         service = packet_get_string(NULL);
 151         method = packet_get_string(NULL);
 152         debug("userauth-request for user %s service %s method %s", user, service, method);
 153         debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
 154
 155         if ((style = strchr(user, ':')) != NULL)
 156                 *style++ = 0;
 157
 158         if (authctxt->attempt++ == 0) {
 159                 /* setup auth context */
 160                 authctxt->pw = PRIVSEP(getpwnamallow(user));
 161                 authctxt->user = xstrdup(user);
 162                 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
 163                         authctxt->valid = 1;
 164                         debug2("input_userauth_request: setting up authctxt for %s", user);
 165                 } else {
 166                         logit("input_userauth_request: invalid user %s", user);
 167                         authctxt->pw = fakepw();
 168 #ifdef SSH_AUDIT_EVENTS
 169                         PRIVSEP(audit_event(SSH_INVALID_USER));
 170 #endif
 171                 }
 172 #ifdef USE_PAM
 173                 if (options.use_pam)
 174                         PRIVSEP(start_pam(authctxt));
 175 #endif
 176                 setproctitle("%s%s", authctxt->valid ? user : "unknown",
 177                     use_privsep ? " [net]" : "");
 178                 authctxt->service = xstrdup(service);
 179                 authctxt->style = style ? xstrdup(style) : NULL;
 180                 if (use_privsep)
 181                         mm_inform_authserv(service, style);
 182         } else if (strcmp(user, authctxt->user) != 0 ||
 183             strcmp(service, authctxt->service) != 0) {
 184                 packet_disconnect("Change of username or service not allowed: "
 185                     "(%s,%s) -> (%s,%s)",
 186                     authctxt->user, authctxt->service, user, service);
 187         }
 188         /* reset state */
 189         auth2_challenge_stop(authctxt);
 190
 191 #ifdef GSSAPI
 192         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 193         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 194 #endif
 195
 196         authctxt->postponed = 0;
 197
 198         /* try to authenticate user */
 199         m = authmethod_lookup(method);
 200         if (m != NULL) {
 201                 debug2("input_userauth_request: try method %s", method);
 202                 authenticated = m->userauth(authctxt);
 203         }
 204         userauth_finish(authctxt, authenticated, method);
 205
 206         xfree(service);
 207         xfree(user);
 208         xfree(method);
 209 }
 210
 211 void
 212 userauth_finish(Authctxt *authctxt, int authenticated, char *method)
 213 {
 214         char *methods;
 215
 216         if (!authctxt->valid && authenticated)
 217                 fatal("INTERNAL ERROR: authenticated invalid user %s",
 218                     authctxt->user);
 219
 220         /* Special handling for root */
 221         if (authenticated && authctxt->pw->pw_uid == 0 &&
 222             !auth_root_allowed(method)) {
 223                 authenticated = 0;
 224 #ifdef SSH_AUDIT_EVENTS
 225                 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 226 #endif
 227         }
 228
 229 #ifdef USE_PAM
 230         if (options.use_pam && authenticated) {
 231                 if (!PRIVSEP(do_pam_account())) {
 232                         /* if PAM returned a message, send it to the user */
 233                         if (buffer_len(&loginmsg) > 0) {
 234                                 buffer_append(&loginmsg, "\0", 1);
 235                                 userauth_send_banner(buffer_ptr(&loginmsg));
 236                                 packet_write_wait();
 237                         }
 238                         fatal("Access denied for user %s by PAM account "
 239                             "configuration", authctxt->user);
 240                 }
 241         }
 242 #endif
 243
 244 #ifdef _UNICOS
 245         if (authenticated && cray_access_denied(authctxt->user)) {
 246                 authenticated = 0;
 247                 fatal("Access denied for user %s.",authctxt->user);
 248         }
 249 #endif /* _UNICOS */
 250
 251         /* Log before sending the reply */
 252         auth_log(authctxt, authenticated, method, " ssh2");
 253
 254         if (authctxt->postponed)
 255                 return;
 256
 257         /* XXX todo: check if multiple auth methods are needed */
 258         if (authenticated == 1) {
 259                 /* turn off userauth */
 260                 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
 261                 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
 262                 packet_send();
 263                 packet_write_wait();
 264                 /* now we can break out */
 265                 authctxt->success = 1;
 266         } else {
 267                 if (authctxt->failures++ > options.max_authtries) {
 268 #ifdef SSH_AUDIT_EVENTS
 269                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 270 #endif
 271                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 272                 }
 273                 methods = authmethods_get();
 274                 packet_start(SSH2_MSG_USERAUTH_FAILURE);
 275                 packet_put_cstring(methods);
 276                 packet_put_char(0);     /* XXX partial success, unused */
 277                 packet_send();
 278                 packet_write_wait();
 279                 xfree(methods);
 280         }
 281 }
 282
 283 #define DELIM   ","
 284
 285 static char *
 286 authmethods_get(void)
 287 {
 288         Buffer b;
 289         char *list;
 290         int i;
 291
 292         buffer_init(&b);
 293         for (i = 0; authmethods[i] != NULL; i++) {
 294                 if (strcmp(authmethods[i]->name, "none") == 0)
 295                         continue;
 296                 if (authmethods[i]->enabled != NULL &&
 297                     *(authmethods[i]->enabled) != 0) {
 298                         if (buffer_len(&b) > 0)
 299                                 buffer_append(&b, ",", 1);
 300                         buffer_append(&b, authmethods[i]->name,
 301                             strlen(authmethods[i]->name));
 302                 }
 303         }
 304         buffer_append(&b, "\0", 1);
 305         list = xstrdup(buffer_ptr(&b));
 306         buffer_free(&b);
 307         return list;
 308 }
 309
 310 static Authmethod *
 311 authmethod_lookup(const char *name)
 312 {
 313         int i;
 314
 315         if (name != NULL)
 316                 for (i = 0; authmethods[i] != NULL; i++)
 317                         if (authmethods[i]->enabled != NULL &&
 318                             *(authmethods[i]->enabled) != 0 &&
 319                             strcmp(name, authmethods[i]->name) == 0)
 320                                 return authmethods[i];
 321         debug2("Unrecognized authentication method name: %s",
 322             name ? name : "NULL");
 323         return NULL;
 324 }