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, MAXHOSTNAMELEN)) { 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 405