crypto/openssh/gss-serv.c

   1 /* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 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 "sshkey.h"
  40 #include "hostfile.h"
  41 #include "auth.h"
  42 #include "log.h"
  43 #include "channels.h"
  44 #include "session.h"
  45 #include "misc.h"
  46 #include "servconf.h"
  47
  48 #include "ssh-gss.h"
  49
  50 extern ServerOptions options;
  51
  52 static ssh_gssapi_client gssapi_client =
  53     { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
  54     GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
  55
  56 ssh_gssapi_mech gssapi_null_mech =
  57     { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
  58
  59 #ifdef KRB5
  60 extern ssh_gssapi_mech gssapi_kerberos_mech;
  61 #endif
  62
  63 ssh_gssapi_mech* supported_mechs[]= {
  64 #ifdef KRB5
  65         &gssapi_kerberos_mech,
  66 #endif
  67         &gssapi_null_mech,
  68 };
  69
  70 /*
  71  * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
  72  * list of supported mechanisms before privsep is set up.
  73  */
  74 static gss_OID_set supported_oids;
  75
  76 void
  77 ssh_gssapi_prepare_supported_oids(void)
  78 {
  79         ssh_gssapi_supported_oids(&supported_oids);
  80 }
  81
  82 OM_uint32
  83 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
  84 {
  85         if (supported_oids == NULL)
  86                 ssh_gssapi_prepare_supported_oids();
  87         return gss_test_oid_set_member(ms, member, supported_oids, present);
  88 }
  89
  90 /*
  91  * Acquire credentials for a server running on the current host.
  92  * Requires that the context structure contains a valid OID
  93  */
  94
  95 /* Returns a GSSAPI error code */
  96 /* Privileged (called from ssh_gssapi_server_ctx) */
  97 static OM_uint32
  98 ssh_gssapi_acquire_cred(Gssctxt *ctx)
  99 {
 100         OM_uint32 status;
 101         char lname[NI_MAXHOST];
 102         gss_OID_set oidset;
 103
 104         if (options.gss_strict_acceptor) {
 105                 gss_create_empty_oid_set(&status, &oidset);
 106                 gss_add_oid_set_member(&status, ctx->oid, &oidset);
 107
 108                 if (gethostname(lname, HOST_NAME_MAX)) {
 109                         gss_release_oid_set(&status, &oidset);
 110                         return (-1);
 111                 }
 112
 113                 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
 114                         gss_release_oid_set(&status, &oidset);
 115                         return (ctx->major);
 116                 }
 117
 118                 if ((ctx->major = gss_acquire_cred(&ctx->minor,
 119                     ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
 120                     NULL, NULL)))
 121                         ssh_gssapi_error(ctx);
 122
 123                 gss_release_oid_set(&status, &oidset);
 124                 return (ctx->major);
 125         } else {
 126                 ctx->name = GSS_C_NO_NAME;
 127                 ctx->creds = GSS_C_NO_CREDENTIAL;
 128         }
 129         return GSS_S_COMPLETE;
 130 }
 131
 132 /* Privileged */
 133 OM_uint32
 134 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
 135 {
 136         if (*ctx)
 137                 ssh_gssapi_delete_ctx(ctx);
 138         ssh_gssapi_build_ctx(ctx);
 139         ssh_gssapi_set_oid(*ctx, oid);
 140         return (ssh_gssapi_acquire_cred(*ctx));
 141 }
 142
 143 /* Unprivileged */
 144 void
 145 ssh_gssapi_supported_oids(gss_OID_set *oidset)
 146 {
 147         int i = 0;
 148         OM_uint32 min_status;
 149         int present;
 150         gss_OID_set supported;
 151
 152         gss_create_empty_oid_set(&min_status, oidset);
 153         gss_indicate_mechs(&min_status, &supported);
 154
 155         while (supported_mechs[i]->name != NULL) {
 156                 if (GSS_ERROR(gss_test_oid_set_member(&min_status,
 157                     &supported_mechs[i]->oid, supported, &present)))
 158                         present = 0;
 159                 if (present)
 160                         gss_add_oid_set_member(&min_status,
 161                             &supported_mechs[i]->oid, oidset);
 162                 i++;
 163         }
 164
 165         gss_release_oid_set(&min_status, &supported);
 166 }
 167
 168
 169 /* Wrapper around accept_sec_context
 170  * Requires that the context contains:
 171  *    oid
 172  *    credentials       (from ssh_gssapi_acquire_cred)
 173  */
 174 /* Privileged */
 175 OM_uint32
 176 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
 177     gss_buffer_desc *send_tok, OM_uint32 *flags)
 178 {
 179         OM_uint32 status;
 180         gss_OID mech;
 181
 182         ctx->major = gss_accept_sec_context(&ctx->minor,
 183             &ctx->context, ctx->creds, recv_tok,
 184             GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
 185             send_tok, flags, NULL, &ctx->client_creds);
 186
 187         if (GSS_ERROR(ctx->major))
 188                 ssh_gssapi_error(ctx);
 189
 190         if (ctx->client_creds)
 191                 debug("Received some client credentials");
 192         else
 193                 debug("Got no client credentials");
 194
 195         status = ctx->major;
 196
 197         /* Now, if we're complete and we have the right flags, then
 198          * we flag the user as also having been authenticated
 199          */
 200
 201         if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
 202             (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
 203                 if (ssh_gssapi_getclient(ctx, &gssapi_client))
 204                         fatal("Couldn't convert client name");
 205         }
 206
 207         return (status);
 208 }
 209
 210 /*
 211  * This parses an exported name, extracting the mechanism specific portion
 212  * to use for ACL checking. It verifies that the name belongs the mechanism
 213  * originally selected.
 214  */
 215 static OM_uint32
 216 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
 217 {
 218         u_char *tok;
 219         OM_uint32 offset;
 220         OM_uint32 oidl;
 221
 222         tok = ename->value;
 223
 224         /*
 225          * Check that ename is long enough for all of the fixed length
 226          * header, and that the initial ID bytes are correct
 227          */
 228
 229         if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
 230                 return GSS_S_FAILURE;
 231
 232         /*
 233          * Extract the OID, and check it. Here GSSAPI breaks with tradition
 234          * and does use the OID type and length bytes. To confuse things
 235          * there are two lengths - the first including these, and the
 236          * second without.
 237          */
 238
 239         oidl = get_u16(tok+2); /* length including next two bytes */
 240         oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
 241
 242         /*
 243          * Check the BER encoding for correct type and length, that the
 244          * string is long enough and that the OID matches that in our context
 245          */
 246         if (tok[4] != 0x06 || tok[5] != oidl ||
 247             ename->length < oidl+6 ||
 248             !ssh_gssapi_check_oid(ctx, tok+6, oidl))
 249                 return GSS_S_FAILURE;
 250
 251         offset = oidl+6;
 252
 253         if (ename->length < offset+4)
 254                 return GSS_S_FAILURE;
 255
 256         name->length = get_u32(tok+offset);
 257         offset += 4;
 258
 259         if (UINT_MAX - offset < name->length)
 260                 return GSS_S_FAILURE;
 261         if (ename->length < offset+name->length)
 262                 return GSS_S_FAILURE;
 263
 264         name->value = xmalloc(name->length+1);
 265         memcpy(name->value, tok+offset, name->length);
 266         ((char *)name->value)[name->length] = 0;
 267
 268         return GSS_S_COMPLETE;
 269 }
 270
 271 /* Extract the client details from a given context. This can only reliably
 272  * be called once for a context */
 273
 274 /* Privileged (called from accept_secure_ctx) */
 275 OM_uint32
 276 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
 277 {
 278         int i = 0;
 279
 280         gss_buffer_desc ename;
 281
 282         client->mech = NULL;
 283
 284         while (supported_mechs[i]->name != NULL) {
 285                 if (supported_mechs[i]->oid.length == ctx->oid->length &&
 286                     (memcmp(supported_mechs[i]->oid.elements,
 287                     ctx->oid->elements, ctx->oid->length) == 0))
 288                         client->mech = supported_mechs[i];
 289                 i++;
 290         }
 291
 292         if (client->mech == NULL)
 293                 return GSS_S_FAILURE;
 294
 295         if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
 296             &client->displayname, NULL))) {
 297                 ssh_gssapi_error(ctx);
 298                 return (ctx->major);
 299         }
 300
 301         if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
 302             &ename))) {
 303                 ssh_gssapi_error(ctx);
 304                 return (ctx->major);
 305         }
 306
 307         if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
 308             &client->exportedname))) {
 309                 return (ctx->major);
 310         }
 311
 312         /* We can't copy this structure, so we just move the pointer to it */
 313         client->creds = ctx->client_creds;
 314         ctx->client_creds = GSS_C_NO_CREDENTIAL;
 315         return (ctx->major);
 316 }
 317
 318 /* As user - called on fatal/exit */
 319 void
 320 ssh_gssapi_cleanup_creds(void)
 321 {
 322         if (gssapi_client.store.filename != NULL) {
 323                 /* Unlink probably isn't sufficient */
 324                 debug("removing gssapi cred file\"%s\"",
 325                     gssapi_client.store.filename);
 326                 unlink(gssapi_client.store.filename);
 327         }
 328 }
 329
 330 /* As user */
 331 void
 332 ssh_gssapi_storecreds(void)
 333 {
 334         if (gssapi_client.mech && gssapi_client.mech->storecreds) {
 335                 (*gssapi_client.mech->storecreds)(&gssapi_client);
 336         } else
 337                 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
 338 }
 339
 340 /* This allows GSSAPI methods to do things to the child's environment based
 341  * on the passed authentication process and credentials.
 342  */
 343 /* As user */
 344 void
 345 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
 346 {
 347
 348         if (gssapi_client.store.envvar != NULL &&
 349             gssapi_client.store.envval != NULL) {
 350                 debug("Setting %s to %s", gssapi_client.store.envvar,
 351                     gssapi_client.store.envval);
 352                 child_set_env(envp, envsizep, gssapi_client.store.envvar,
 353                     gssapi_client.store.envval);
 354         }
 355 }
 356
 357 /* Privileged */
 358 int
 359 ssh_gssapi_userok(char *user)
 360 {
 361         OM_uint32 lmin;
 362
 363         if (gssapi_client.exportedname.length == 0 ||
 364             gssapi_client.exportedname.value == NULL) {
 365                 debug("No suitable client data");
 366                 return 0;
 367         }
 368         if (gssapi_client.mech && gssapi_client.mech->userok)
 369                 if ((*gssapi_client.mech->userok)(&gssapi_client, user))
 370                         return 1;
 371                 else {
 372                         /* Destroy delegated credentials if userok fails */
 373                         gss_release_buffer(&lmin, &gssapi_client.displayname);
 374                         gss_release_buffer(&lmin, &gssapi_client.exportedname);
 375                         gss_release_cred(&lmin, &gssapi_client.creds);
 376                         explicit_bzero(&gssapi_client,
 377                             sizeof(ssh_gssapi_client));
 378                         return 0;
 379                 }
 380         else
 381                 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
 382         return (0);
 383 }
 384
 385 /* Privileged */
 386 OM_uint32
 387 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
 388 {
 389         ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
 390             gssbuf, gssmic, NULL);
 391
 392         return (ctx->major);
 393 }
 394
 395 /* Privileged */
 396 const char *ssh_gssapi_displayname(void)
 397 {
 398         if (gssapi_client.displayname.length == 0 ||
 399             gssapi_client.displayname.value == NULL)
 400                 return NULL;
 401         return (char *)gssapi_client.displayname.value;
 402 }
 403
 404 #endif