1/* $NetBSD: gss-serv.c,v 1.15 2020/05/28 17:05:49 christos Exp $ */ 2/* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 djm Exp $ */ 3 4/* 5 * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28#include "includes.h" 29__RCSID("$NetBSD: gss-serv.c,v 1.15 2020/05/28 17:05:49 christos Exp $"); 30 31#include <sys/param.h> 32#include <sys/types.h> 33#include <sys/queue.h> 34 35#ifdef GSSAPI 36 37#include <string.h> 38#include <unistd.h> 39#include <netdb.h> 40#include <limits.h> 41#include <stdarg.h> 42 43#include "xmalloc.h" 44#include "sshkey.h" 45#include "hostfile.h" 46#include "auth.h" 47#include "log.h" 48#include "channels.h" 49#include "session.h" 50#include "misc.h" 51#include "servconf.h" 52 53#include "ssh-gss.h" 54 55extern ServerOptions options; 56 57static ssh_gssapi_client gssapi_client = 58 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER, 59 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}}; 60 61ssh_gssapi_mech gssapi_null_mech = 62 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL}; 63 64#ifdef KRB5 65extern ssh_gssapi_mech gssapi_kerberos_mech; 66#endif 67 68ssh_gssapi_mech* supported_mechs[]= { 69#ifdef KRB5 70 &gssapi_kerberos_mech, 71#endif 72 &gssapi_null_mech, 73}; 74 75/* 76 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the 77 * list of supported mechanisms before privsep is set up. 78 */ 79static gss_OID_set supported_oids; 80 81void 82ssh_gssapi_prepare_supported_oids(void) 83{ 84 ssh_gssapi_supported_oids(&supported_oids); 85} 86 87OM_uint32 88ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present) 89{ 90 if (supported_oids == NULL) 91 ssh_gssapi_prepare_supported_oids(); 92 return gss_test_oid_set_member(ms, member, supported_oids, present); 93} 94 95/* 96 * Acquire credentials for a server running on the current host. 97 * Requires that the context structure contains a valid OID 98 */ 99 100/* Returns a GSSAPI error code */ 101/* Privileged (called from ssh_gssapi_server_ctx) */ 102static OM_uint32 103ssh_gssapi_acquire_cred(Gssctxt *ctx) 104{ 105 OM_uint32 status; 106 char lname[NI_MAXHOST]; 107 gss_OID_set oidset; 108 109 if (options.gss_strict_acceptor) { 110 gss_create_empty_oid_set(&status, &oidset); 111 gss_add_oid_set_member(&status, ctx->oid, &oidset); 112 113 if (gethostname(lname, MAXHOSTNAMELEN)) { 114 gss_release_oid_set(&status, &oidset); 115 return (-1); 116 } 117 118 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) { 119 gss_release_oid_set(&status, &oidset); 120 return (ctx->major); 121 } 122 123 if ((ctx->major = gss_acquire_cred(&ctx->minor, 124 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds, 125 NULL, NULL))) 126 ssh_gssapi_error(ctx); 127 128 gss_release_oid_set(&status, &oidset); 129 return (ctx->major); 130 } else { 131 ctx->name = GSS_C_NO_NAME; 132 ctx->creds = GSS_C_NO_CREDENTIAL; 133 } 134 return GSS_S_COMPLETE; 135} 136 137/* Privileged */ 138OM_uint32 139ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid) 140{ 141 if (*ctx) 142 ssh_gssapi_delete_ctx(ctx); 143 ssh_gssapi_build_ctx(ctx); 144 ssh_gssapi_set_oid(*ctx, oid); 145 return (ssh_gssapi_acquire_cred(*ctx)); 146} 147 148/* Unprivileged */ 149void 150ssh_gssapi_supported_oids(gss_OID_set *oidset) 151{ 152 int i = 0; 153 OM_uint32 min_status; 154 int present; 155 gss_OID_set supported; 156 157 gss_create_empty_oid_set(&min_status, oidset); 158 gss_indicate_mechs(&min_status, &supported); 159 160 while (supported_mechs[i]->name != NULL) { 161 if (GSS_ERROR(gss_test_oid_set_member(&min_status, 162 &supported_mechs[i]->oid, supported, &present))) 163 present = 0; 164 if (present) 165 gss_add_oid_set_member(&min_status, 166 &supported_mechs[i]->oid, oidset); 167 i++; 168 } 169 170 gss_release_oid_set(&min_status, &supported); 171} 172 173 174/* Wrapper around accept_sec_context 175 * Requires that the context contains: 176 * oid 177 * credentials (from ssh_gssapi_acquire_cred) 178 */ 179/* Privileged */ 180OM_uint32 181ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok, 182 gss_buffer_desc *send_tok, OM_uint32 *flags) 183{ 184 OM_uint32 status; 185 gss_OID mech; 186 187 ctx->major = gss_accept_sec_context(&ctx->minor, 188 &ctx->context, ctx->creds, recv_tok, 189 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech, 190 send_tok, flags, NULL, &ctx->client_creds); 191 192 if (GSS_ERROR(ctx->major)) 193 ssh_gssapi_error(ctx); 194 195 if (ctx->client_creds) 196 debug("Received some client credentials"); 197 else 198 debug("Got no client credentials"); 199 200 status = ctx->major; 201 202 /* Now, if we're complete and we have the right flags, then 203 * we flag the user as also having been authenticated 204 */ 205 206 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) && 207 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) { 208 if (ssh_gssapi_getclient(ctx, &gssapi_client)) 209 fatal("Couldn't convert client name"); 210 } 211 212 return (status); 213} 214 215/* 216 * This parses an exported name, extracting the mechanism specific portion 217 * to use for ACL checking. It verifies that the name belongs the mechanism 218 * originally selected. 219 */ 220static OM_uint32 221ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name) 222{ 223 u_char *tok; 224 OM_uint32 offset; 225 OM_uint32 oidl; 226 227 tok = ename->value; 228 229 /* 230 * Check that ename is long enough for all of the fixed length 231 * header, and that the initial ID bytes are correct 232 */ 233 234 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0) 235 return GSS_S_FAILURE; 236 237 /* 238 * Extract the OID, and check it. Here GSSAPI breaks with tradition 239 * and does use the OID type and length bytes. To confuse things 240 * there are two lengths - the first including these, and the 241 * second without. 242 */ 243 244 oidl = get_u16(tok+2); /* length including next two bytes */ 245 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */ 246 247 /* 248 * Check the BER encoding for correct type and length, that the 249 * string is long enough and that the OID matches that in our context 250 */ 251 if (tok[4] != 0x06 || tok[5] != oidl || 252 ename->length < oidl+6 || 253 !ssh_gssapi_check_oid(ctx, tok+6, oidl)) 254 return GSS_S_FAILURE; 255 256 offset = oidl+6; 257 258 if (ename->length < offset+4) 259 return GSS_S_FAILURE; 260 261 name->length = get_u32(tok+offset); 262 offset += 4; 263 264 if (UINT_MAX - offset < name->length) 265 return GSS_S_FAILURE; 266 if (ename->length < offset+name->length) 267 return GSS_S_FAILURE; 268 269 name->value = xmalloc(name->length+1); 270 memcpy(name->value, tok+offset, name->length); 271 ((char *)name->value)[name->length] = 0; 272 273 return GSS_S_COMPLETE; 274} 275 276/* Extract the client details from a given context. This can only reliably 277 * be called once for a context */ 278 279/* Privileged (called from accept_secure_ctx) */ 280OM_uint32 281ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client) 282{ 283 int i = 0; 284 285 gss_buffer_desc ename; 286 287 client->mech = NULL; 288 289 while (supported_mechs[i]->name != NULL) { 290 if (supported_mechs[i]->oid.length == ctx->oid->length && 291 (memcmp(supported_mechs[i]->oid.elements, 292 ctx->oid->elements, ctx->oid->length) == 0)) 293 client->mech = supported_mechs[i]; 294 i++; 295 } 296 297 if (client->mech == NULL) 298 return GSS_S_FAILURE; 299 300 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client, 301 &client->displayname, NULL))) { 302 ssh_gssapi_error(ctx); 303 return (ctx->major); 304 } 305 306 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client, 307 &ename))) { 308 ssh_gssapi_error(ctx); 309 return (ctx->major); 310 } 311 312 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename, 313 &client->exportedname))) { 314 return (ctx->major); 315 } 316 317 /* We can't copy this structure, so we just move the pointer to it */ 318 client->creds = ctx->client_creds; 319 ctx->client_creds = GSS_C_NO_CREDENTIAL; 320 return (ctx->major); 321} 322 323/* As user - called on fatal/exit */ 324void 325ssh_gssapi_cleanup_creds(void) 326{ 327 if (gssapi_client.store.filename != NULL) { 328 /* Unlink probably isn't sufficient */ 329 debug("removing gssapi cred file\"%s\"", 330 gssapi_client.store.filename); 331 unlink(gssapi_client.store.filename); 332 } 333} 334 335/* As user */ 336void 337ssh_gssapi_storecreds(void) 338{ 339 if (gssapi_client.mech && gssapi_client.mech->storecreds) { 340 (*gssapi_client.mech->storecreds)(&gssapi_client); 341 } else 342 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism"); 343} 344 345/* This allows GSSAPI methods to do things to the child's environment based 346 * on the passed authentication process and credentials. 347 */ 348/* As user */ 349void 350ssh_gssapi_do_child(char ***envp, u_int *envsizep) 351{ 352 353 if (gssapi_client.store.envvar != NULL && 354 gssapi_client.store.envval != NULL) { 355 debug("Setting %s to %s", gssapi_client.store.envvar, 356 gssapi_client.store.envval); 357 child_set_env(envp, envsizep, gssapi_client.store.envvar, 358 gssapi_client.store.envval); 359 } 360} 361 362/* Privileged */ 363int 364ssh_gssapi_userok(char *user) 365{ 366 OM_uint32 lmin; 367 368 if (gssapi_client.exportedname.length == 0 || 369 gssapi_client.exportedname.value == NULL) { 370 debug("No suitable client data"); 371 return 0; 372 } 373 if (gssapi_client.mech && gssapi_client.mech->userok) 374 if ((*gssapi_client.mech->userok)(&gssapi_client, user)) 375 return 1; 376 else { 377 /* Destroy delegated credentials if userok fails */ 378 gss_release_buffer(&lmin, &gssapi_client.displayname); 379 gss_release_buffer(&lmin, &gssapi_client.exportedname); 380 gss_release_cred(&lmin, &gssapi_client.creds); 381 explicit_bzero(&gssapi_client, 382 sizeof(ssh_gssapi_client)); 383 return 0; 384 } 385 else 386 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism"); 387 return (0); 388} 389 390/* Privileged */ 391OM_uint32 392ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic) 393{ 394 ctx->major = gss_verify_mic(&ctx->minor, ctx->context, 395 gssbuf, gssmic, NULL); 396 397 return (ctx->major); 398} 399 400/* Privileged */ 401const char *ssh_gssapi_displayname(void) 402{ 403 if (gssapi_client.displayname.length == 0 || 404 gssapi_client.displayname.value == NULL) 405 return NULL; 406 return (char *)gssapi_client.displayname.value; 407} 408 409#endif 410