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