crypto/openssh/gss-serv.c

   1 /* $OpenBSD: gss-serv.c,v 1.29 2015/05/22 03:50:02 djm Exp $ */
   2
   3 /*
   4  * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "includes.h"
  28
  29 #ifdef GSSAPI
  30
  31 #include <sys/types.h>
  32
  33 #include <stdarg.h>
  34 #include <string.h>
  35 #include <unistd.h>
  36
  37 #include "openbsd-compat/sys-queue.h"
  38 #include "xmalloc.h"
  39 #include "buffer.h"
  40 #include "key.h"
  41 #include "hostfile.h"
  42 #include "auth.h"
  43 #include "log.h"
  44 #include "channels.h"
  45 #include "session.h"
  46 #include "misc.h"
  47 #include "servconf.h"
  48
  49 #include "ssh-gss.h"
  50
  51 extern ServerOptions options;
  52
  53 static ssh_gssapi_client gssapi_client =
  54     { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
  55     GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
  56
  57 ssh_gssapi_mech gssapi_null_mech =
  58     { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
  59
  60 #ifdef KRB5
  61 extern ssh_gssapi_mech gssapi_kerberos_mech;
  62 #endif
  63
  64 ssh_gssapi_mech* supported_mechs[]= {
  65 #ifdef KRB5
  66         &gssapi_kerberos_mech,
  67 #endif
  68         &gssapi_null_mech,
  69 };
  70
  71 /*
  72  * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
  73  * list of supported mechanisms before privsep is set up.
  74  */
  75 static gss_OID_set supported_oids;
  76
  77 void
  78 ssh_gssapi_prepare_supported_oids(void)
  79 {
  80         ssh_gssapi_supported_oids(&supported_oids);
  81 }
  82
  83 OM_uint32
  84 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
  85 {
  86         if (supported_oids == NULL)
  87                 ssh_gssapi_prepare_supported_oids();
  88         return gss_test_oid_set_member(ms, member, supported_oids, present);
  89 }
  90
  91 /*
  92  * Acquire credentials for a server running on the current host.
  93  * Requires that the context structure contains a valid OID
  94  */
  95
  96 /* Returns a GSSAPI error code */
  97 /* Privileged (called from ssh_gssapi_server_ctx) */
  98 static OM_uint32
  99 ssh_gssapi_acquire_cred(Gssctxt *ctx)
 100 {
 101         OM_uint32 status;
 102         char lname[NI_MAXHOST];
 103         gss_OID_set oidset;
 104
 105         if (options.gss_strict_acceptor) {
 106                 gss_create_empty_oid_set(&status, &oidset);
 107                 gss_add_oid_set_member(&status, ctx->oid, &oidset);
 108
 109                 if (gethostname(lname, MAXHOSTNAMELEN)) {
 110                         gss_release_oid_set(&status, &oidset);
 111                         return (-1);
 112                 }
 113
 114                 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
 115                         gss_release_oid_set(&status, &oidset);
 116                         return (ctx->major);
 117                 }
 118
 119                 if ((ctx->major = gss_acquire_cred(&ctx->minor,
 120                     ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
 121                     NULL, NULL)))
 122                         ssh_gssapi_error(ctx);
 123
 124                 gss_release_oid_set(&status, &oidset);
 125                 return (ctx->major);
 126         } else {
 127                 ctx->name = GSS_C_NO_NAME;
 128                 ctx->creds = GSS_C_NO_CREDENTIAL;
 129         }
 130         return GSS_S_COMPLETE;
 131 }
 132
 133 /* Privileged */
 134 OM_uint32
 135 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
 136 {
 137         if (*ctx)
 138                 ssh_gssapi_delete_ctx(ctx);
 139         ssh_gssapi_build_ctx(ctx);
 140         ssh_gssapi_set_oid(*ctx, oid);
 141         return (ssh_gssapi_acquire_cred(*ctx));
 142 }
 143
 144 /* Unprivileged */
 145 void
 146 ssh_gssapi_supported_oids(gss_OID_set *oidset)
 147 {
 148         int i = 0;
 149         OM_uint32 min_status;
 150         int present;
 151         gss_OID_set supported;
 152
 153         gss_create_empty_oid_set(&min_status, oidset);
 154         gss_indicate_mechs(&min_status, &supported);
 155
 156         while (supported_mechs[i]->name != NULL) {
 157                 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
 158                     &supported_mechs[i]->oid, supported, &present)))
 159                         present = 0;
 160                 if (present)
 161                         gss_add_oid_set_member(&min_status,
 162                             &supported_mechs[i]->oid, oidset);
 163                 i++;
 164         }
 165
 166         gss_release_oid_set(&min_status, &supported);
 167 }
 168
 169
 170 /* Wrapper around accept_sec_context
 171  * Requires that the context contains:
 172  *    oid
 173  *    credentials       (from ssh_gssapi_acquire_cred)
 174  */
 175 /* Privileged */
 176 OM_uint32
 177 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
 178     gss_buffer_desc *send_tok, OM_uint32 *flags)
 179 {
 180         OM_uint32 status;
 181         gss_OID mech;
 182
 183         ctx->major = gss_accept_sec_context(&ctx->minor,
 184             &ctx->context, ctx->creds, recv_tok,
 185             GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
 186             send_tok, flags, NULL, &ctx->client_creds);
 187
 188         if (GSS_ERROR(ctx->major))
 189                 ssh_gssapi_error(ctx);
 190
 191         if (ctx->client_creds)
 192                 debug("Received some client credentials");
 193         else
 194                 debug("Got no client credentials");
 195
 196         status = ctx->major;
 197
 198         /* Now, if we're complete and we have the right flags, then
 199          * we flag the user as also having been authenticated
 200          */
 201
 202         if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
 203             (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
 204                 if (ssh_gssapi_getclient(ctx, &gssapi_client))
 205                         fatal("Couldn't convert client name");
 206         }
 207
 208         return (status);
 209 }
 210
 211 /*
 212  * This parses an exported name, extracting the mechanism specific portion
 213  * to use for ACL checking. It verifies that the name belongs the mechanism
 214  * originally selected.
 215  */
 216 static OM_uint32
 217 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
 218 {
 219         u_char *tok;
 220         OM_uint32 offset;
 221         OM_uint32 oidl;
 222
 223         tok = ename->value;
 224
 225         /*
 226          * Check that ename is long enough for all of the fixed length
 227          * header, and that the initial ID bytes are correct
 228          */
 229
 230         if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
 231                 return GSS_S_FAILURE;
 232
 233         /*
 234          * Extract the OID, and check it. Here GSSAPI breaks with tradition
 235          * and does use the OID type and length bytes. To confuse things
 236          * there are two lengths - the first including these, and the
 237          * second without.
 238          */
 239
 240         oidl = get_u16(tok+2); /* length including next two bytes */
 241         oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
 242
 243         /*
 244          * Check the BER encoding for correct type and length, that the
 245          * string is long enough and that the OID matches that in our context
 246          */
 247         if (tok[4] != 0x06 || tok[5] != oidl ||
 248             ename->length < oidl+6 ||
 249             !ssh_gssapi_check_oid(ctx, tok+6, oidl))
 250                 return GSS_S_FAILURE;
 251
 252         offset = oidl+6;
 253
 254         if (ename->length < offset+4)
 255                 return GSS_S_FAILURE;
 256
 257         name->length = get_u32(tok+offset);
 258         offset += 4;
 259
 260         if (UINT_MAX - offset < name->length)
 261                 return GSS_S_FAILURE;
 262         if (ename->length < offset+name->length)
 263                 return GSS_S_FAILURE;
 264
 265         name->value = xmalloc(name->length+1);
 266         memcpy(name->value, tok+offset, name->length);
 267         ((char *)name->value)[name->length] = 0;
 268
 269         return GSS_S_COMPLETE;
 270 }
 271
 272 /* Extract the client details from a given context. This can only reliably
 273  * be called once for a context */
 274
 275 /* Privileged (called from accept_secure_ctx) */
 276 OM_uint32
 277 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
 278 {
 279         int i = 0;
 280
 281         gss_buffer_desc ename;
 282
 283         client->mech = NULL;
 284
 285         while (supported_mechs[i]->name != NULL) {
 286                 if (supported_mechs[i]->oid.length == ctx->oid->length &&
 287                     (memcmp(supported_mechs[i]->oid.elements,
 288                     ctx->oid->elements, ctx->oid->length) == 0))
 289                         client->mech = supported_mechs[i];
 290                 i++;
 291         }
 292
 293         if (client->mech == NULL)
 294                 return GSS_S_FAILURE;
 295
 296         if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
 297             &client->displayname, NULL))) {
 298                 ssh_gssapi_error(ctx);
 299                 return (ctx->major);
 300         }
 301
 302         if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
 303             &ename))) {
 304                 ssh_gssapi_error(ctx);
 305                 return (ctx->major);
 306         }
 307
 308         if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
 309             &client->exportedname))) {
 310                 return (ctx->major);
 311         }
 312
 313         /* We can't copy this structure, so we just move the pointer to it */
 314         client->creds = ctx->client_creds;
 315         ctx->client_creds = GSS_C_NO_CREDENTIAL;
 316         return (ctx->major);
 317 }
 318
 319 /* As user - called on fatal/exit */
 320 void
 321 ssh_gssapi_cleanup_creds(void)
 322 {
 323         if (gssapi_client.store.filename != NULL) {
 324                 /* Unlink probably isn't sufficient */
 325                 debug("removing gssapi cred file\"%s\"",
 326                     gssapi_client.store.filename);
 327                 unlink(gssapi_client.store.filename);
 328         }
 329 }
 330
 331 /* As user */
 332 void
 333 ssh_gssapi_storecreds(void)
 334 {
 335         if (gssapi_client.mech && gssapi_client.mech->storecreds) {
 336                 (*gssapi_client.mech->storecreds)(&gssapi_client);
 337         } else
 338                 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
 339 }
 340
 341 /* This allows GSSAPI methods to do things to the childs environment based
 342  * on the passed authentication process and credentials.
 343  */
 344 /* As user */
 345 void
 346 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
 347 {
 348
 349         if (gssapi_client.store.envvar != NULL &&
 350             gssapi_client.store.envval != NULL) {
 351                 debug("Setting %s to %s", gssapi_client.store.envvar,
 352                     gssapi_client.store.envval);
 353                 child_set_env(envp, envsizep, gssapi_client.store.envvar,
 354                     gssapi_client.store.envval);
 355         }
 356 }
 357
 358 /* Privileged */
 359 int
 360 ssh_gssapi_userok(char *user)
 361 {
 362         OM_uint32 lmin;
 363
 364         if (gssapi_client.exportedname.length == 0 ||
 365             gssapi_client.exportedname.value == NULL) {
 366                 debug("No suitable client data");
 367                 return 0;
 368         }
 369         if (gssapi_client.mech && gssapi_client.mech->userok)
 370                 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
 371                         return 1;
 372                 else {
 373                         /* Destroy delegated credentials if userok fails */
 374                         gss_release_buffer(&lmin, &gssapi_client.displayname);
 375                         gss_release_buffer(&lmin, &gssapi_client.exportedname);
 376                         gss_release_cred(&lmin, &gssapi_client.creds);
 377                         explicit_bzero(&gssapi_client,
 378                             sizeof(ssh_gssapi_client));
 379                         return 0;
 380                 }
 381         else
 382                 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
 383         return (0);
 384 }
 385
 386 /* Privileged */
 387 OM_uint32
 388 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
 389 {
 390         ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
 391             gssbuf, gssmic, NULL);
 392
 393         return (ctx->major);
 394 }
 395
 396 #endif