1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2018 */
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 */
83 void auth_heimdal_gssapi_init(auth_instance *ablock) {}
84 int auth_heimdal_gssapi_server(auth_instance *ablock, uschar *data) {return 0;}
85 int auth_heimdal_gssapi_client(auth_instance *ablock, void * sx,
86 int timeout, uschar *buffer, int buffsize) {return 0;}
87 void auth_heimdal_gssapi_version_report(FILE *f) {}
89 #else /*!MACRO_PREDEF*/
93 /* "Globals" for managing the heimdal_gssapi interface. */
95 /* Utility functions */
97 exim_heimdal_error_debug(const char *, krb5_context, krb5_error_code);
99 exim_gssapi_error_defer(rmark, OM_uint32, OM_uint32, const char *, ...)
100 PRINTF_FUNCTION(4, 5);
102 #define EmptyBuf(buf) do { buf.value = NULL; buf.length = 0; } while (0)
105 /*************************************************
106 * Initialization entry point *
107 *************************************************/
109 /* Called for each instance, after its options have been read, to
110 enable consistency checks to be done, or anything else that needs
113 /* Heimdal provides a GSSAPI extension method for setting the keytab;
114 in the init, we mostly just use raw krb5 methods so that we can report
115 the keytab contents, for -D+auth debugging. */
118 auth_heimdal_gssapi_init(auth_instance *ablock)
120 krb5_context context;
122 krb5_kt_cursor cursor;
123 krb5_keytab_entry entry;
125 char *principal, *enctype_s;
126 const char *k_keytab_typed_name = NULL;
127 auth_heimdal_gssapi_options_block *ob =
128 (auth_heimdal_gssapi_options_block *)(ablock->options_block);
130 ablock->server = FALSE;
131 ablock->client = FALSE;
133 if (!ob->server_service || !*ob->server_service)
135 HDEBUG(D_auth) debug_printf("heimdal: missing server_service\n");
139 krc = krb5_init_context(&context);
143 HDEBUG(D_auth) debug_printf("heimdal: failed to initialise krb5 context: %s\n",
148 if (ob->server_keytab)
150 k_keytab_typed_name = CCS string_sprintf("file:%s", expand_string(ob->server_keytab));
151 HDEBUG(D_auth) debug_printf("heimdal: using keytab %s\n", k_keytab_typed_name);
152 krc = krb5_kt_resolve(context, k_keytab_typed_name, &keytab);
155 HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_resolve", context, krc);
161 HDEBUG(D_auth) debug_printf("heimdal: using system default keytab\n");
162 krc = krb5_kt_default(context, &keytab);
165 HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_default", context, krc);
172 /* http://www.h5l.org/manual/HEAD/krb5/krb5_keytab_intro.html */
173 krc = krb5_kt_start_seq_get(context, keytab, &cursor);
175 exim_heimdal_error_debug("krb5_kt_start_seq_get", context, krc);
178 while ((krc = krb5_kt_next_entry(context, keytab, &entry, &cursor)) == 0)
180 principal = enctype_s = NULL;
181 krb5_unparse_name(context, entry.principal, &principal);
182 krb5_enctype_to_string(context, entry.keyblock.keytype, &enctype_s);
183 debug_printf("heimdal: keytab principal: %s vno=%d type=%s\n",
184 principal ? principal : "??",
186 enctype_s ? enctype_s : "??");
189 krb5_kt_free_entry(context, &entry);
191 krc = krb5_kt_end_seq_get(context, keytab, &cursor);
193 exim_heimdal_error_debug("krb5_kt_end_seq_get", context, krc);
197 krc = krb5_kt_close(context, keytab);
199 HDEBUG(D_auth) exim_heimdal_error_debug("krb5_kt_close", context, krc);
201 krb5_free_context(context);
203 ablock->server = TRUE;
208 exim_heimdal_error_debug(const char *label,
209 krb5_context context, krb5_error_code err)
212 kerrsc = krb5_get_error_message(context, err);
213 debug_printf("heimdal %s: %s\n", label, kerrsc ? kerrsc : "unknown error");
214 krb5_free_error_message(context, kerrsc);
217 /*************************************************
218 * Server entry point *
219 *************************************************/
221 /* For interface, see auths/README */
224 OM_uint32: portable type for unsigned int32
225 gss_buffer_desc / *gss_buffer_t: hold/point-to size_t .length & void *value
226 -- all strings/etc passed in should go through one of these
227 -- when allocated by gssapi, release with gss_release_buffer()
231 auth_heimdal_gssapi_server(auth_instance *ablock, uschar *initial_data)
233 gss_name_t gclient = GSS_C_NO_NAME;
234 gss_name_t gserver = GSS_C_NO_NAME;
235 gss_cred_id_t gcred = GSS_C_NO_CREDENTIAL;
236 gss_ctx_id_t gcontext = GSS_C_NO_CONTEXT;
237 uschar *ex_server_str;
238 gss_buffer_desc gbufdesc = GSS_C_EMPTY_BUFFER;
239 gss_buffer_desc gbufdesc_in = GSS_C_EMPTY_BUFFER;
240 gss_buffer_desc gbufdesc_out = GSS_C_EMPTY_BUFFER;
242 OM_uint32 maj_stat, min_stat;
244 uschar *tmp1, *tmp2, *from_client;
245 auth_heimdal_gssapi_options_block *ob =
246 (auth_heimdal_gssapi_options_block *)(ablock->options_block);
247 BOOL handled_empty_ir;
248 rmark store_reset_point;
250 uschar sasl_config[4];
251 uschar requested_qop;
253 store_reset_point = store_mark();
256 debug_printf("heimdal: initialising auth context for %s\n", ablock->name);
258 /* Construct our gss_name_t gserver describing ourselves */
259 tmp1 = expand_string(ob->server_service);
260 tmp2 = expand_string(ob->server_hostname);
261 ex_server_str = string_sprintf("%s@%s", tmp1, tmp2);
262 gbufdesc.value = (void *) ex_server_str;
263 gbufdesc.length = Ustrlen(ex_server_str);
264 maj_stat = gss_import_name(&min_stat,
265 &gbufdesc, GSS_C_NT_HOSTBASED_SERVICE, &gserver);
266 if (GSS_ERROR(maj_stat))
267 return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat,
268 "gss_import_name(%s)", CS gbufdesc.value);
270 /* Use a specific keytab, if specified */
271 if (ob->server_keytab)
273 keytab = expand_string(ob->server_keytab);
274 maj_stat = gsskrb5_register_acceptor_identity(CCS keytab);
275 if (GSS_ERROR(maj_stat))
276 return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat,
277 "registering keytab \"%s\"", keytab);
279 debug_printf("heimdal: using keytab \"%s\"\n", keytab);
282 /* Acquire our credentials */
283 maj_stat = gss_acquire_cred(&min_stat,
284 gserver, /* desired name */
286 GSS_C_NULL_OID_SET, /* desired mechs */
287 GSS_C_ACCEPT, /* cred usage */
289 NULL /* actual mechs */,
290 NULL /* time rec */);
291 if (GSS_ERROR(maj_stat))
292 return exim_gssapi_error_defer(store_reset_point, maj_stat, min_stat,
293 "gss_acquire_cred(%s)", ex_server_str);
295 maj_stat = gss_release_name(&min_stat, &gserver);
297 HDEBUG(D_auth) debug_printf("heimdal: have server credentials.\n");
299 /* Loop talking to client */
301 from_client = initial_data;
302 handled_empty_ir = FALSE;
305 /* buffer sizes: auth_get_data() uses big_buffer, which we grow per
306 GSSAPI RFC in _init, if needed, to meet the SHOULD size of 64KB.
307 (big_buffer starts life at the MUST size of 16KB). */
310 0: getting initial data from client to feed into GSSAPI
311 1: iterating for as long as GSS_S_CONTINUE_NEEDED
312 2: GSS_S_COMPLETE, SASL wrapping for authz and qop to send to client
313 3: unpick final auth message from client
314 4: break/finish (non-step)
320 if (!from_client || *from_client == '\0')
322 if (handled_empty_ir)
324 HDEBUG(D_auth) debug_printf("gssapi: repeated empty input, grr.\n");
330 HDEBUG(D_auth) debug_printf("gssapi: missing initial response, nudging.\n");
331 error_out = auth_get_data(&from_client, US"", 0);
334 handled_empty_ir = TRUE;
338 /* We should now have the opening data from the client, base64-encoded. */
340 HDEBUG(D_auth) debug_printf("heimdal: have initial client data\n");
344 gbufdesc_in.length = b64decode(from_client, USS &gbufdesc_in.value);
347 maj_stat = gss_release_name(&min_stat, &gclient);
348 gclient = GSS_C_NO_NAME;
350 maj_stat = gss_accept_sec_context(&min_stat,
351 &gcontext, /* context handle */
352 gcred, /* acceptor cred handle */
353 &gbufdesc_in, /* input from client */
354 GSS_C_NO_CHANNEL_BINDINGS, /* XXX fixme: use the channel bindings from GnuTLS */
355 &gclient, /* client identifier */
356 &mech_type, /* mechanism in use */
357 &gbufdesc_out, /* output to send to client */
358 NULL, /* return flags */
360 NULL /* delegated cred_handle */
362 if (GSS_ERROR(maj_stat))
364 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
365 "gss_accept_sec_context()");
369 if (gbufdesc_out.length != 0)
371 error_out = auth_get_data(&from_client,
372 gbufdesc_out.value, gbufdesc_out.length);
376 gss_release_buffer(&min_stat, &gbufdesc_out);
377 EmptyBuf(gbufdesc_out);
379 if (maj_stat == GSS_S_COMPLETE)
382 HDEBUG(D_auth) debug_printf("heimdal: GSS complete\n");
385 HDEBUG(D_auth) debug_printf("heimdal: need more data\n");
389 memset(sasl_config, 0xFF, 4);
390 /* draft-ietf-sasl-gssapi-06.txt defines bitmasks for first octet
391 0x01 No security layer
392 0x02 Integrity protection
393 0x04 Confidentiality protection
395 The remaining three octets are the maximum buffer size for wrapped
397 sasl_config[0] = 0x01; /* Exim does not wrap/unwrap SASL layers after auth */
398 gbufdesc.value = (void *) sasl_config;
400 maj_stat = gss_wrap(&min_stat,
402 0, /* conf_req_flag: integrity only */
403 GSS_C_QOP_DEFAULT, /* qop requested */
404 &gbufdesc, /* message to protect */
405 NULL, /* conf_state: no confidentiality applied */
406 &gbufdesc_out /* output buffer */
408 if (GSS_ERROR(maj_stat))
410 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
411 "gss_wrap(SASL state after auth)");
416 HDEBUG(D_auth) debug_printf("heimdal SASL: requesting QOP with no security layers\n");
418 error_out = auth_get_data(&from_client,
419 gbufdesc_out.value, gbufdesc_out.length);
423 gss_release_buffer(&min_stat, &gbufdesc_out);
424 EmptyBuf(gbufdesc_out);
429 gbufdesc_in.length = b64decode(from_client, USS &gbufdesc_in.value);
430 maj_stat = gss_unwrap(&min_stat,
432 &gbufdesc_in, /* data from client */
433 &gbufdesc_out, /* results */
434 NULL, /* conf state */
437 if (GSS_ERROR(maj_stat))
439 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
440 "gss_unwrap(final SASL message from client)");
444 if (gbufdesc_out.length < 4)
447 debug_printf("gssapi: final message too short; "
448 "need flags, buf sizes and optional authzid\n");
453 requested_qop = (CS gbufdesc_out.value)[0];
454 if ((requested_qop & 0x01) == 0)
457 debug_printf("gssapi: client requested security layers (%x)\n",
458 (unsigned int) requested_qop);
463 for (int i = 0; i < AUTH_VARS; i++) auth_vars[i] = NULL;
467 The SASL provided identifier is an unverified authzid.
468 GSSAPI provides us with a verified identifier, but it might be empty
472 /* $auth2 is authzid requested at SASL layer */
473 if (gbufdesc_out.length > 4)
475 expand_nlength[2] = gbufdesc_out.length - 4;
476 auth_vars[1] = expand_nstring[2] =
477 string_copyn((US gbufdesc_out.value) + 4, expand_nlength[2]);
481 gss_release_buffer(&min_stat, &gbufdesc_out);
482 EmptyBuf(gbufdesc_out);
484 /* $auth1 is GSSAPI display name */
485 maj_stat = gss_display_name(&min_stat,
489 if (GSS_ERROR(maj_stat))
491 auth_vars[1] = expand_nstring[2] = NULL;
493 exim_gssapi_error_defer(NULL, maj_stat, min_stat,
494 "gss_display_name(client identifier)");
499 expand_nlength[1] = gbufdesc_out.length;
500 auth_vars[0] = expand_nstring[1] =
501 string_copyn(gbufdesc_out.value, gbufdesc_out.length);
503 if (expand_nmax == 0) /* should be: authzid was empty */
506 expand_nlength[2] = expand_nlength[1];
507 auth_vars[1] = expand_nstring[2] = string_copyn(expand_nstring[1], expand_nlength[1]);
509 debug_printf("heimdal SASL: empty authzid, set to dup of GSSAPI display name\n");
513 debug_printf("heimdal SASL: happy with client request\n"
514 " auth1 (verified GSSAPI display-name): \"%s\"\n"
515 " auth2 (unverified SASL requested authzid): \"%s\"\n",
516 auth_vars[0], auth_vars[1]);
526 maj_stat = gss_release_cred(&min_stat, &gcred);
529 gss_release_name(&min_stat, &gclient);
530 gclient = GSS_C_NO_NAME;
532 if (gbufdesc_out.length)
534 gss_release_buffer(&min_stat, &gbufdesc_out);
535 EmptyBuf(gbufdesc_out);
537 if (gcontext != GSS_C_NO_CONTEXT)
538 gss_delete_sec_context(&min_stat, &gcontext, GSS_C_NO_BUFFER);
540 store_reset(store_reset_point);
545 /* Auth succeeded, check server_condition */
546 return auth_check_serv_cond(ablock);
551 exim_gssapi_error_defer(rmark store_reset_point,
552 OM_uint32 major, OM_uint32 minor,
553 const char *format, ...)
556 OM_uint32 maj_stat, min_stat;
557 OM_uint32 msgcontext = 0;
558 gss_buffer_desc status_string;
563 va_start(ap, format);
564 g = string_vformat(NULL, SVFMT_EXTEND|SVFMT_REBUFFER, format, ap);
568 auth_defer_msg = NULL;
571 maj_stat = gss_display_status(&min_stat,
572 major, GSS_C_GSS_CODE, GSS_C_NO_OID, &msgcontext, &status_string);
575 auth_defer_msg = string_copy(US status_string.value);
577 HDEBUG(D_auth) debug_printf("heimdal %s: %.*s\n",
578 string_from_gstring(g), (int)status_string.length,
579 CS status_string.value);
580 gss_release_buffer(&min_stat, &status_string);
582 } while (msgcontext != 0);
584 if (store_reset_point)
585 store_reset(store_reset_point);
590 /*************************************************
591 * Client entry point *
592 *************************************************/
594 /* For interface, see auths/README */
597 auth_heimdal_gssapi_client(
598 auth_instance *ablock, /* authenticator block */
599 void * sx, /* connection */
600 int timeout, /* command timeout */
601 uschar *buffer, /* buffer for reading response */
602 int buffsize) /* size of buffer */
605 debug_printf("Client side NOT IMPLEMENTED: you should not see this!\n");
606 /* NOT IMPLEMENTED */
610 /*************************************************
612 *************************************************/
615 auth_heimdal_gssapi_version_report(FILE *f)
617 /* No build-time constants available unless we link against libraries at
618 build-time and export the result as a string into a header ourselves. */
619 fprintf(f, "Library version: Heimdal: Runtime: %s\n"
621 heimdal_version, heimdal_long_version);
624 #endif /*!MACRO_PREDEF*/
625 #endif /* AUTH_HEIMDAL_GSSAPI */
627 /* End of heimdal_gssapi.c */