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