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 397