1 /* $NetBSD: gss-serv.c,v 1.13 2019/01/27 02:08:33 pgoyette Exp $ */ 2 /* $OpenBSD: gss-serv.c,v 1.31 2018/07/09 21:37:55 markus 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 1.13 2019/01/27 02:08:33 pgoyette 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 42 #include "xmalloc.h" 43 #include "sshkey.h" 44 #include "hostfile.h" 45 #include "auth.h" 46 #include "log.h" 47 #include "channels.h" 48 #include "session.h" 49 #include "misc.h" 50 #include "servconf.h" 51 52 #include "ssh-gss.h" 53 54 extern ServerOptions options; 55 56 static ssh_gssapi_client gssapi_client = 57 { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER, 58 GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}}; 59 60 ssh_gssapi_mech gssapi_null_mech = 61 { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL}; 62 63 #ifdef KRB5 64 extern ssh_gssapi_mech gssapi_kerberos_mech; 65 #endif 66 67 ssh_gssapi_mech* supported_mechs[]= { 68 #ifdef KRB5 69 &gssapi_kerberos_mech, 70 #endif 71 &gssapi_null_mech, 72 }; 73 74 /* 75 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the 76 * list of supported mechanisms before privsep is set up. 77 */ 78 static gss_OID_set supported_oids; 79 80 void 81 ssh_gssapi_prepare_supported_oids(void) 82 { 83 ssh_gssapi_supported_oids(&supported_oids); 84 } 85 86 OM_uint32 87 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present) 88 { 89 if (supported_oids == NULL) 90 ssh_gssapi_prepare_supported_oids(); 91 return gss_test_oid_set_member(ms, member, supported_oids, present); 92 } 93 94 /* 95 * Acquire credentials for a server running on the current host. 96 * Requires that the context structure contains a valid OID 97 */ 98 99 /* Returns a GSSAPI error code */ 100 /* Privileged (called from ssh_gssapi_server_ctx) */ 101 static OM_uint32 102 ssh_gssapi_acquire_cred(Gssctxt *ctx) 103 { 104 OM_uint32 status; 105 char lname[NI_MAXHOST]; 106 gss_OID_set oidset; 107 108 if (options.gss_strict_acceptor) { 109 gss_create_empty_oid_set(&status, &oidset); 110 gss_add_oid_set_member(&status, ctx->oid, &oidset); 111 112 if (gethostname(lname, MAXHOSTNAMELEN)) { 113 gss_release_oid_set(&status, &oidset); 114 return (-1); 115 } 116 117 if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) { 118 gss_release_oid_set(&status, &oidset); 119 return (ctx->major); 120 } 121 122 if ((ctx->major = gss_acquire_cred(&ctx->minor, 123 ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds, 124 NULL, NULL))) 125 ssh_gssapi_error(ctx); 126 127 gss_release_oid_set(&status, &oidset); 128 return (ctx->major); 129 } else { 130 ctx->name = GSS_C_NO_NAME; 131 ctx->creds = GSS_C_NO_CREDENTIAL; 132 } 133 return GSS_S_COMPLETE; 134 } 135 136 /* Privileged */ 137 OM_uint32 138 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid) 139 { 140 if (*ctx) 141 ssh_gssapi_delete_ctx(ctx); 142 ssh_gssapi_build_ctx(ctx); 143 ssh_gssapi_set_oid(*ctx, oid); 144 return (ssh_gssapi_acquire_cred(*ctx)); 145 } 146 147 /* Unprivileged */ 148 void 149 ssh_gssapi_supported_oids(gss_OID_set *oidset) 150 { 151 int i = 0; 152 OM_uint32 min_status; 153 int present; 154 gss_OID_set supported; 155 156 gss_create_empty_oid_set(&min_status, oidset); 157 gss_indicate_mechs(&min_status, &supported); 158 159 while (supported_mechs[i]->name != NULL) { 160 if (GSS_ERROR(gss_test_oid_set_member(&min_status, 161 &supported_mechs[i]->oid, supported, &present))) 162 present = 0; 163 if (present) 164 gss_add_oid_set_member(&min_status, 165 &supported_mechs[i]->oid, oidset); 166 i++; 167 } 168 169 gss_release_oid_set(&min_status, &supported); 170 } 171 172 173 /* Wrapper around accept_sec_context 174 * Requires that the context contains: 175 * oid 176 * credentials (from ssh_gssapi_acquire_cred) 177 */ 178 /* Privileged */ 179 OM_uint32 180 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok, 181 gss_buffer_desc *send_tok, OM_uint32 *flags) 182 { 183 OM_uint32 status; 184 gss_OID mech; 185 186 ctx->major = gss_accept_sec_context(&ctx->minor, 187 &ctx->context, ctx->creds, recv_tok, 188 GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech, 189 send_tok, flags, NULL, &ctx->client_creds); 190 191 if (GSS_ERROR(ctx->major)) 192 ssh_gssapi_error(ctx); 193 194 if (ctx->client_creds) 195 debug("Received some client credentials"); 196 else 197 debug("Got no client credentials"); 198 199 status = ctx->major; 200 201 /* Now, if we're complete and we have the right flags, then 202 * we flag the user as also having been authenticated 203 */ 204 205 if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) && 206 (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) { 207 if (ssh_gssapi_getclient(ctx, &gssapi_client)) 208 fatal("Couldn't convert client name"); 209 } 210 211 return (status); 212 } 213 214 /* 215 * This parses an exported name, extracting the mechanism specific portion 216 * to use for ACL checking. It verifies that the name belongs the mechanism 217 * originally selected. 218 */ 219 static OM_uint32 220 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name) 221 { 222 u_char *tok; 223 OM_uint32 offset; 224 OM_uint32 oidl; 225 226 tok = ename->value; 227 228 /* 229 * Check that ename is long enough for all of the fixed length 230 * header, and that the initial ID bytes are correct 231 */ 232 233 if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0) 234 return GSS_S_FAILURE; 235 236 /* 237 * Extract the OID, and check it. Here GSSAPI breaks with tradition 238 * and does use the OID type and length bytes. To confuse things 239 * there are two lengths - the first including these, and the 240 * second without. 241 */ 242 243 oidl = get_u16(tok+2); /* length including next two bytes */ 244 oidl = oidl-2; /* turn it into the _real_ length of the variable OID */ 245 246 /* 247 * Check the BER encoding for correct type and length, that the 248 * string is long enough and that the OID matches that in our context 249 */ 250 if (tok[4] != 0x06 || tok[5] != oidl || 251 ename->length < oidl+6 || 252 !ssh_gssapi_check_oid(ctx, tok+6, oidl)) 253 return GSS_S_FAILURE; 254 255 offset = oidl+6; 256 257 if (ename->length < offset+4) 258 return GSS_S_FAILURE; 259 260 name->length = get_u32(tok+offset); 261 offset += 4; 262 263 if (UINT_MAX - offset < name->length) 264 return GSS_S_FAILURE; 265 if (ename->length < offset+name->length) 266 return GSS_S_FAILURE; 267 268 name->value = xmalloc(name->length+1); 269 memcpy(name->value, tok+offset, name->length); 270 ((char *)name->value)[name->length] = 0; 271 272 return GSS_S_COMPLETE; 273 } 274 275 /* Extract the client details from a given context. This can only reliably 276 * be called once for a context */ 277 278 /* Privileged (called from accept_secure_ctx) */ 279 OM_uint32 280 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client) 281 { 282 int i = 0; 283 284 gss_buffer_desc ename; 285 286 client->mech = NULL; 287 288 while (supported_mechs[i]->name != NULL) { 289 if (supported_mechs[i]->oid.length == ctx->oid->length && 290 (memcmp(supported_mechs[i]->oid.elements, 291 ctx->oid->elements, ctx->oid->length) == 0)) 292 client->mech = supported_mechs[i]; 293 i++; 294 } 295 296 if (client->mech == NULL) 297 return GSS_S_FAILURE; 298 299 if ((ctx->major = gss_display_name(&ctx->minor, ctx->client, 300 &client->displayname, NULL))) { 301 ssh_gssapi_error(ctx); 302 return (ctx->major); 303 } 304 305 if ((ctx->major = gss_export_name(&ctx->minor, ctx->client, 306 &ename))) { 307 ssh_gssapi_error(ctx); 308 return (ctx->major); 309 } 310 311 if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename, 312 &client->exportedname))) { 313 return (ctx->major); 314 } 315 316 /* We can't copy this structure, so we just move the pointer to it */ 317 client->creds = ctx->client_creds; 318 ctx->client_creds = GSS_C_NO_CREDENTIAL; 319 return (ctx->major); 320 } 321 322 /* As user - called on fatal/exit */ 323 void 324 ssh_gssapi_cleanup_creds(void) 325 { 326 if (gssapi_client.store.filename != NULL) { 327 /* Unlink probably isn't sufficient */ 328 debug("removing gssapi cred file\"%s\"", 329 gssapi_client.store.filename); 330 unlink(gssapi_client.store.filename); 331 } 332 } 333 334 /* As user */ 335 void 336 ssh_gssapi_storecreds(void) 337 { 338 if (gssapi_client.mech && gssapi_client.mech->storecreds) { 339 (*gssapi_client.mech->storecreds)(&gssapi_client); 340 } else 341 debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism"); 342 } 343 344 /* This allows GSSAPI methods to do things to the childs environment based 345 * on the passed authentication process and credentials. 346 */ 347 /* As user */ 348 void 349 ssh_gssapi_do_child(char ***envp, u_int *envsizep) 350 { 351 352 if (gssapi_client.store.envvar != NULL && 353 gssapi_client.store.envval != NULL) { 354 debug("Setting %s to %s", gssapi_client.store.envvar, 355 gssapi_client.store.envval); 356 child_set_env(envp, envsizep, gssapi_client.store.envvar, 357 gssapi_client.store.envval); 358 } 359 } 360 361 /* Privileged */ 362 int 363 ssh_gssapi_userok(char *user) 364 { 365 OM_uint32 lmin; 366 367 if (gssapi_client.exportedname.length == 0 || 368 gssapi_client.exportedname.value == NULL) { 369 debug("No suitable client data"); 370 return 0; 371 } 372 if (gssapi_client.mech && gssapi_client.mech->userok) 373 if ((*gssapi_client.mech->userok)(&gssapi_client, user)) 374 return 1; 375 else { 376 /* Destroy delegated credentials if userok fails */ 377 gss_release_buffer(&lmin, &gssapi_client.displayname); 378 gss_release_buffer(&lmin, &gssapi_client.exportedname); 379 gss_release_cred(&lmin, &gssapi_client.creds); 380 explicit_bzero(&gssapi_client, 381 sizeof(ssh_gssapi_client)); 382 return 0; 383 } 384 else 385 debug("ssh_gssapi_userok: Unknown GSSAPI mechanism"); 386 return (0); 387 } 388 389 /* Privileged */ 390 OM_uint32 391 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic) 392 { 393 ctx->major = gss_verify_mic(&ctx->minor, ctx->context, 394 gssbuf, gssmic, NULL); 395 396 return (ctx->major); 397 } 398 399 /* Privileged */ 400 const char *ssh_gssapi_displayname(void) 401 { 402 if (gssapi_client.displayname.length == 0 || 403 gssapi_client.displayname.value == NULL) 404 return NULL; 405 return (char *)gssapi_client.displayname.value; 406 } 407 408 #endif 409