1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2015 */
6 /* See the file NOTICE for conditions of use and distribution. */
8 /* Copyright (c) Twitter Inc 2012
9 Author: Phil Pennock <pdp@exim.org> */
10 /* Copyright (c) Phil Pennock 2012 */
12 /* Interface to Heimdal library for GSSAPI authentication. */
14 /* Naming and rationale
16 Sensibly, this integration would be deferred to a SASL library, but none
17 of them appear to offer keytab file selection interfaces in their APIs. It
18 might be that this driver only requires minor modification to work with MIT
21 Heimdal provides a number of interfaces for various forms of authentication.
22 As GS2 does not appear to provide keytab control interfaces either, we may
23 end up supporting that too. It's possible that we could trivially expand to
24 support NTLM support via Heimdal, etc. Rather than try to be too generic
25 immediately, this driver is directly only supporting GSSAPI.
27 Without rename, we could add an option for GS2 support in the future.
32 * mailcheck-imap (Perl, client-side, written by me years ago)
33 * gsasl driver (GPL, server-side)
34 * heimdal sources and man-pages, plus http://www.h5l.org/manual/
35 * FreeBSD man-pages (very informative!)
36 * http://www.ggf.org/documents/GFD.24.pdf confirming GSS_KRB5_REGISTER_ACCEPTOR_IDENTITY_X
37 semantics, that found by browsing Heimdal source to find how to set the keytab; however,
38 after multiple attempts I failed to get that to work and instead switched to
39 gsskrb5_register_acceptor_identity().
44 #ifndef AUTH_HEIMDAL_GSSAPI
45 /* dummy function to satisfy compilers when we link in an "empty" file. */
46 static void dummy(int x);
47 static void dummy2(int x) { dummy(x-1); }
48 static void dummy(int x) { dummy2(x-1); }
51 #include <gssapi/gssapi.h>
52 #include <gssapi/gssapi_krb5.h>
54 /* for the _init debugging */
57 #include "heimdal_gssapi.h"
59 /* Authenticator-specific options. */
60 optionlist auth_heimdal_gssapi_options[] = {
61 { "server_hostname", opt_stringptr,
62 (void *)(offsetof(auth_heimdal_gssapi_options_block, server_hostname)) },
63 { "server_keytab", opt_stringptr,
64 (void *)(offsetof(auth_heimdal_gssapi_options_block, server_keytab)) },
65 { "server_service", opt_stringptr,
66 (void *)(offsetof(auth_heimdal_gssapi_options_block, server_service)) }
69 int auth_heimdal_gssapi_options_count =
70 sizeof(auth_heimdal_gssapi_options)/sizeof(optionlist);
72 /* Defaults for the authenticator-specific options. */
73 auth_heimdal_gssapi_options_block auth_heimdal_gssapi_option_defaults = {
74 US"$primary_hostname", /* server_hostname */
75 NULL, /* server_keytab */
76 US"smtp", /* server_service */
79 /* "Globals" for managing the heimdal_gssapi interface. */
81 /* Utility functions */
83 exim_heimdal_error_debug(const char *, krb5_context, krb5_error_code);
85 exim_gssapi_error_defer(uschar *, OM_uint32, OM_uint32, const char *, ...)
86 PRINTF_FUNCTION(4, 5);
88 #define EmptyBuf(buf) do { buf.value = NULL; buf.length = 0; } while (0)
91 /*************************************************
92 * Initialization entry point *
93 *************************************************/
95 /* Called for each instance, after its options have been read, to
96 enable consistency checks to be done, or anything else that needs
99 /* Heimdal provides a GSSAPI extension method for setting the keytab;
100 in the init, we mostly just use raw krb5 methods so that we can report
101 the keytab contents, for -D+auth debugging. */
104 auth_heimdal_gssapi_init(auth_instance *ablock)
106 krb5_context context;
108 krb5_kt_cursor cursor;
109 krb5_keytab_entry entry;
111 char *principal, *enctype_s;
112 const char *k_keytab_typed_name = NULL;
113 auth_heimdal_gssapi_options_block *ob =
114 (auth_heimdal_gssapi_options_block *)(ablock->options_block);
116 ablock->server = FALSE;
117 ablock->client = FALSE;
119 if (!ob->server_service || !*ob->server_service) {
120 HDEBUG(D_auth) debug_printf("heimdal: missing server_service\n");
124 krc = krb5_init_context(&context);
127 HDEBUG(D_auth) debug_printf("heimdal: failed to initialise krb5 context: %s\n",
132 if (ob->server_keytab) {
133 k_keytab_typed_name = CCS string_sprintf("file:%s", expand_string(ob->server_keytab));
134 HDEBUG(D_auth) debug_printf("heimdal: using keytab %s\n", k_keytab_typed_name);
135 krc = krb5_kt_resolve(context, k_keytab_typed_name, &keytab);
137 HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_resolve", context, krc);
141 HDEBUG(D_auth) debug_printf("heimdal: using system default keytab\n");
142 krc = krb5_kt_default(context, &keytab);
144 HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_default", context, krc);
150 /* http://www.h5l.org/manual/HEAD/krb5/krb5_keytab_intro.html */
151 krc = krb5_kt_start_seq_get(context, keytab, &cursor);
153 exim_heimdal_error_debug("krb5_kt_start_seq_get", context, krc);
155 while ((krc = krb5_kt_next_entry(context, keytab, &entry, &cursor)) == 0) {
156 principal = enctype_s = NULL;
157 krb5_unparse_name(context, entry.principal, &principal);
158 krb5_enctype_to_string(context, entry.keyblock.keytype, &enctype_s);
159 debug_printf("heimdal: keytab principal: %s vno=%d type=%s\n",
160 principal ? principal : "??",
162 enctype_s ? enctype_s : "??");
165 krb5_kt_free_entry(context, &entry);
167 krc = krb5_kt_end_seq_get(context, keytab, &cursor);
169 exim_heimdal_error_debug("krb5_kt_end_seq_get", context, krc);
173 krc = krb5_kt_close(context, keytab);
175 HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_close", context, krc);
177 krb5_free_context(context);
179 /* RFC 4121 section 5.2, SHOULD support 64K input buffers */
180 if (big_buffer_size < (64 * 1024)) {
182 big_buffer_size = 64 * 1024;
183 newbuf = store_malloc(big_buffer_size);
184 store_free(big_buffer);
188 ablock->server = TRUE;
193 exim_heimdal_error_debug(const char *label,
194 krb5_context context, krb5_error_code err)
197 kerrsc = krb5_get_error_message(context, err);
198 debug_printf("heimdal %s: %s\n", label, kerrsc ? kerrsc : "unknown error");
199 krb5_free_error_message(context, kerrsc);
202 /*************************************************
203 * Server entry point *
204 *************************************************/
206 /* For interface, see auths/README */
209 OM_uint32: portable type for unsigned int32
210 gss_buffer_desc / *gss_buffer_t: hold/point-to size_t .length & void *value
211 -- all strings/etc passed in should go through one of these
212 -- when allocated by gssapi, release with gss_release_buffer()
216 auth_heimdal_gssapi_server(auth_instance *ablock, uschar *initial_data)
218 gss_name_t gclient = GSS_C_NO_NAME;
219 gss_name_t gserver = GSS_C_NO_NAME;
220 gss_cred_id_t gcred = GSS_C_NO_CREDENTIAL;
221 gss_ctx_id_t gcontext = GSS_C_NO_CONTEXT;
222 uschar *ex_server_str;
223 gss_buffer_desc gbufdesc = GSS_C_EMPTY_BUFFER;
224 gss_buffer_desc gbufdesc_in = GSS_C_EMPTY_BUFFER;
225 gss_buffer_desc gbufdesc_out = GSS_C_EMPTY_BUFFER;
227 OM_uint32 maj_stat, min_stat;
228 int step, error_out, i;
229 uschar *tmp1, *tmp2, *from_client;
230 auth_heimdal_gssapi_options_block *ob =
231 (auth_heimdal_gssapi_options_block *)(ablock->options_block);
232 BOOL handled_empty_ir;
233 uschar *store_reset_point;
235 uschar sasl_config[4];
236 uschar requested_qop;
238 store_reset_point = store_get(0);
241 debug_printf("heimdal: initialising auth context for %s\n", ablock->name);
243 /* Construct our gss_name_t gserver describing ourselves */
244 tmp1 = expand_string(ob->server_service);
245 tmp2 = expand_string(ob->server_hostname);
246 ex_server_str = string_sprintf("%s@%s", tmp1, tmp2);
247 gbufdesc.value = (void *) ex_server_str;
248 gbufdesc.length = Ustrlen(ex_server_str);
249 maj_stat = gss_import_name(&min_stat,
250 &gbufdesc, GSS_C_NT_HOSTBASED_SERVICE, &gserver);
251 if (GSS_ERROR(maj_stat))
252 return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat,
253 "gss_import_name(%s)", CS gbufdesc.value);
255 /* Use a specific keytab, if specified */
256 if (ob->server_keytab) {
257 keytab = expand_string(ob->server_keytab);
258 maj_stat = gsskrb5_register_acceptor_identity(CCS keytab);
259 if (GSS_ERROR(maj_stat))
260 return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat,
261 "registering keytab \"%s\"", keytab);
263 debug_printf("heimdal: using keytab \"%s\"\n", keytab);
266 /* Acquire our credentials */
267 maj_stat = gss_acquire_cred(&min_stat,
268 gserver, /* desired name */
270 GSS_C_NULL_OID_SET, /* desired mechs */
271 GSS_C_ACCEPT, /* cred usage */
273 NULL /* actual mechs */,
274 NULL /* time rec */);
275 if (GSS_ERROR(maj_stat))
276 return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat,
277 "gss_acquire_cred(%s)", ex_server_str);
279 maj_stat = gss_release_name(&min_stat, &gserver);
281 HDEBUG(D_auth) debug_printf("heimdal: have server credentials.\n");
283 /* Loop talking to client */
285 from_client = initial_data;
286 handled_empty_ir = FALSE;
289 /* buffer sizes: auth_get_data() uses big_buffer, which we grow per
290 GSSAPI RFC in _init, if needed, to meet the SHOULD size of 64KB.
291 (big_buffer starts life at the MUST size of 16KB). */
294 0: getting initial data from client to feed into GSSAPI
295 1: iterating for as long as GSS_S_CONTINUE_NEEDED
296 2: GSS_S_COMPLETE, SASL wrapping for authz and qop to send to client
297 3: unpick final auth message from client
298 4: break/finish (non-step)
303 if (!from_client || *from_client == '\0') {
304 if (handled_empty_ir) {
305 HDEBUG(D_auth) debug_printf("gssapi: repeated empty input, grr.\n");
309 HDEBUG(D_auth) debug_printf("gssapi: missing initial response, nudging.\n");
310 error_out = auth_get_data(&from_client, US"", 0);
313 handled_empty_ir = TRUE;
317 /* We should now have the opening data from the client, base64-encoded. */
319 HDEBUG(D_auth) debug_printf("heimdal: have initial client data\n");
323 gbufdesc_in.length = b64decode(from_client, USS &gbufdesc_in.value);
325 maj_stat = gss_release_name(&min_stat, &gclient);
326 gclient = GSS_C_NO_NAME;
328 maj_stat = gss_accept_sec_context(&min_stat,
329 &gcontext, /* context handle */
330 gcred, /* acceptor cred handle */
331 &gbufdesc_in, /* input from client */
332 GSS_C_NO_CHANNEL_BINDINGS, /* XXX fixme: use the channel bindings from GnuTLS */
333 &gclient, /* client identifier */
334 &mech_type, /* mechanism in use */
335 &gbufdesc_out, /* output to send to client */
336 NULL, /* return flags */
338 NULL /* delegated cred_handle */
340 if (GSS_ERROR(maj_stat)) {
341 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
342 "gss_accept_sec_context()");
346 if (&gbufdesc_out.length != 0) {
347 error_out = auth_get_data(&from_client,
348 gbufdesc_out.value, gbufdesc_out.length);
352 gss_release_buffer(&min_stat, &gbufdesc_out);
353 EmptyBuf(gbufdesc_out);
355 if (maj_stat == GSS_S_COMPLETE) {
357 HDEBUG(D_auth) debug_printf("heimdal: GSS complete\n");
359 HDEBUG(D_auth) debug_printf("heimdal: need more data\n");
364 memset(sasl_config, 0xFF, 4);
365 /* draft-ietf-sasl-gssapi-06.txt defines bitmasks for first octet
366 0x01 No security layer
367 0x02 Integrity protection
368 0x04 Confidentiality protection
370 The remaining three octets are the maximum buffer size for wrapped
372 sasl_config[0] = 0x01; /* Exim does not wrap/unwrap SASL layers after auth */
373 gbufdesc.value = (void *) sasl_config;
375 maj_stat = gss_wrap(&min_stat,
377 0, /* conf_req_flag: integrity only */
378 GSS_C_QOP_DEFAULT, /* qop requested */
379 &gbufdesc, /* message to protect */
380 NULL, /* conf_state: no confidentiality applied */
381 &gbufdesc_out /* output buffer */
383 if (GSS_ERROR(maj_stat)) {
384 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
385 "gss_wrap(SASL state after auth)");
390 HDEBUG(D_auth) debug_printf("heimdal SASL: requesting QOP with no security layers\n");
392 error_out = auth_get_data(&from_client,
393 gbufdesc_out.value, gbufdesc_out.length);
397 gss_release_buffer(&min_stat, &gbufdesc_out);
398 EmptyBuf(gbufdesc_out);
403 gbufdesc_in.length = b64decode(from_client, USS &gbufdesc_in.value);
404 maj_stat = gss_unwrap(&min_stat,
406 &gbufdesc_in, /* data from client */
407 &gbufdesc_out, /* results */
408 NULL, /* conf state */
411 if (GSS_ERROR(maj_stat)) {
412 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
413 "gss_unwrap(final SASL message from client)");
417 if (gbufdesc_out.length < 4) {
419 debug_printf("gssapi: final message too short; "
420 "need flags, buf sizes and optional authzid\n");
425 requested_qop = (CS gbufdesc_out.value)[0];
426 if ((requested_qop & 0x01) == 0) {
428 debug_printf("gssapi: client requested security layers (%x)\n",
429 (unsigned int) requested_qop);
434 for (i = 0; i < AUTH_VARS; i++) auth_vars[i] = NULL;
438 The SASL provided identifier is an unverified authzid.
439 GSSAPI provides us with a verified identifier, but it might be empty
443 /* $auth2 is authzid requested at SASL layer */
444 if (gbufdesc_out.length > 4) {
445 expand_nlength[2] = gbufdesc_out.length - 4;
446 auth_vars[1] = expand_nstring[2] =
447 string_copyn((US gbufdesc_out.value) + 4, expand_nlength[2]);
451 gss_release_buffer(&min_stat, &gbufdesc_out);
452 EmptyBuf(gbufdesc_out);
454 /* $auth1 is GSSAPI display name */
455 maj_stat = gss_display_name(&min_stat,
459 if (GSS_ERROR(maj_stat)) {
460 auth_vars[1] = expand_nstring[2] = NULL;
462 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
463 "gss_display_name(client identifier)");
468 expand_nlength[1] = gbufdesc_out.length;
469 auth_vars[0] = expand_nstring[1] =
470 string_copyn(gbufdesc_out.value, gbufdesc_out.length);
472 if (expand_nmax == 0) { /* should be: authzid was empty */
474 expand_nlength[2] = expand_nlength[1];
475 auth_vars[1] = expand_nstring[2] = string_copyn(expand_nstring[1], expand_nlength[1]);
477 debug_printf("heimdal SASL: empty authzid, set to dup of GSSAPI display name\n");
481 debug_printf("heimdal SASL: happy with client request\n"
482 " auth1 (verified GSSAPI display-name): \"%s\"\n"
483 " auth2 (unverified SASL requested authzid): \"%s\"\n",
484 auth_vars[0], auth_vars[1]);
494 maj_stat = gss_release_cred(&min_stat, &gcred);
496 gss_release_name(&min_stat, &gclient);
497 gclient = GSS_C_NO_NAME;
499 if (gbufdesc_out.length) {
500 gss_release_buffer(&min_stat, &gbufdesc_out);
501 EmptyBuf(gbufdesc_out);
503 if (gcontext != GSS_C_NO_CONTEXT) {
504 gss_delete_sec_context(&min_stat, &gcontext, GSS_C_NO_BUFFER);
507 store_reset(store_reset_point);
512 /* Auth succeeded, check server_condition */
513 return auth_check_serv_cond(ablock);
518 exim_gssapi_error_defer(uschar *store_reset_point,
519 OM_uint32 major, OM_uint32 minor,
520 const char *format, ...)
523 uschar buffer[STRING_SPRINTF_BUFFER_SIZE];
524 OM_uint32 maj_stat, min_stat;
525 OM_uint32 msgcontext = 0;
526 gss_buffer_desc status_string;
528 va_start(ap, format);
529 if (!string_vformat(buffer, sizeof(buffer), format, ap))
530 log_write(0, LOG_MAIN|LOG_PANIC_DIE,
531 "exim_gssapi_error_defer expansion larger than %lu",
535 auth_defer_msg = NULL;
538 maj_stat = gss_display_status(&min_stat,
539 major, GSS_C_GSS_CODE, GSS_C_NO_OID,
540 &msgcontext, &status_string);
542 if (auth_defer_msg == NULL) {
543 auth_defer_msg = string_copy(US status_string.value);
546 HDEBUG(D_auth) debug_printf("heimdal %s: %.*s\n",
547 buffer, (int)status_string.length, CS status_string.value);
548 gss_release_buffer(&min_stat, &status_string);
550 } while (msgcontext != 0);
552 if (store_reset_point)
553 store_reset(store_reset_point);
558 /*************************************************
559 * Client entry point *
560 *************************************************/
562 /* For interface, see auths/README */
565 auth_heimdal_gssapi_client(
566 auth_instance *ablock, /* authenticator block */
567 smtp_inblock *inblock, /* connection inblock */
568 smtp_outblock *outblock, /* connection outblock */
569 int timeout, /* command timeout */
570 uschar *buffer, /* buffer for reading response */
571 int buffsize) /* size of buffer */
574 debug_printf("Client side NOT IMPLEMENTED: you should not see this!\n");
575 /* NOT IMPLEMENTED */
579 /*************************************************
581 *************************************************/
584 auth_heimdal_gssapi_version_report(FILE *f)
586 /* No build-time constants available unless we link against libraries at
587 build-time and export the result as a string into a header ourselves. */
588 fprintf(f, "Library version: Heimdal: Runtime: %s\n"
590 heimdal_version, heimdal_long_version);
593 #endif /* AUTH_HEIMDAL_GSSAPI */
595 /* End of heimdal_gssapi.c */