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 GNU SASL library for generic authentication. */
16 GNU SASL does not provide authentication data itself, so we have to expose
17 that decision to configuration. For some mechanisms, we need to act much
18 like plaintext. For others, we only need to be able to provide some
19 evaluated data on demand. There's no abstracted way (ie, without hardcoding
20 knowledge of authenticators here) to know which need what properties; we
21 can't query a session or the library for "we will need these for mechanism X".
23 So: we always require server_condition, even if sometimes it will just be
24 set as "yes". We do provide a number of other hooks, which might not make
25 sense in all contexts. For some, we can do checks at init time.
31 /* dummy function to satisfy compilers when we link in an "empty" file. */
32 static void dummy(int x);
33 static void dummy2(int x) { dummy(x-1); }
34 static void dummy(int x) { dummy2(x-1); }
38 #include "gsasl_exim.h"
40 /* Authenticator-specific options. */
41 /* I did have server_*_condition options for various mechanisms, but since
42 we only ever handle one mechanism at a time, I didn't see the point in keeping
43 that. In case someone sees a point, I've left the condition_check() API
45 optionlist auth_gsasl_options[] = {
46 { "server_channelbinding", opt_bool,
47 (void *)(offsetof(auth_gsasl_options_block, server_channelbinding)) },
48 { "server_hostname", opt_stringptr,
49 (void *)(offsetof(auth_gsasl_options_block, server_hostname)) },
50 { "server_mech", opt_stringptr,
51 (void *)(offsetof(auth_gsasl_options_block, server_mech)) },
52 { "server_password", opt_stringptr,
53 (void *)(offsetof(auth_gsasl_options_block, server_password)) },
54 { "server_realm", opt_stringptr,
55 (void *)(offsetof(auth_gsasl_options_block, server_realm)) },
56 { "server_scram_iter", opt_stringptr,
57 (void *)(offsetof(auth_gsasl_options_block, server_scram_iter)) },
58 { "server_scram_salt", opt_stringptr,
59 (void *)(offsetof(auth_gsasl_options_block, server_scram_salt)) },
60 { "server_service", opt_stringptr,
61 (void *)(offsetof(auth_gsasl_options_block, server_service)) }
63 /* GSASL_SCRAM_SALTED_PASSWORD documented only for client, so not implementing
64 hooks to avoid cleartext passwords in the Exim server. */
66 int auth_gsasl_options_count =
67 sizeof(auth_gsasl_options)/sizeof(optionlist);
69 /* Defaults for the authenticator-specific options. */
70 auth_gsasl_options_block auth_gsasl_option_defaults = {
71 US"smtp", /* server_service */
72 US"$primary_hostname", /* server_hostname */
73 NULL, /* server_realm */
74 NULL, /* server_mech */
75 NULL, /* server_password */
76 NULL, /* server_scram_iter */
77 NULL, /* server_scram_salt */
78 FALSE /* server_channelbinding */
85 void auth_gsasl_init(auth_instance *ablock) {}
86 int auth_gsasl_server(auth_instance *ablock, uschar *data) {return 0;}
87 int auth_gsasl_client(auth_instance *ablock, smtp_inblock *inblock,
88 smtp_outblock *outblock, int timeout, uschar *buffer, int buffsize) {return 0;}
89 void auth_gsasl_version_report(FILE *f) {}
91 #else /*!MACRO_PREDEF*/
95 /* "Globals" for managing the gsasl interface. */
97 static Gsasl *gsasl_ctx = NULL;
99 main_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop);
101 server_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock);
103 client_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock);
105 static BOOL sasl_error_should_defer = FALSE;
106 static Gsasl_property callback_loop = 0;
107 static BOOL checked_server_condition = FALSE;
109 enum { CURRENTLY_SERVER = 1, CURRENTLY_CLIENT = 2 };
111 struct callback_exim_state {
112 auth_instance *ablock;
117 /*************************************************
118 * Initialization entry point *
119 *************************************************/
121 /* Called for each instance, after its options have been read, to
122 enable consistency checks to be done, or anything else that needs
126 auth_gsasl_init(auth_instance *ablock)
130 auth_gsasl_options_block *ob =
131 (auth_gsasl_options_block *)(ablock->options_block);
133 /* As per existing Cyrus glue, use the authenticator's public name as
134 the default for the mechanism name; we don't handle multiple mechanisms
135 in one authenticator, but the same driver can be used multiple times. */
137 if (ob->server_mech == NULL)
138 ob->server_mech = string_copy(ablock->public_name);
140 /* Can get multiple session contexts from one library context, so just
141 initialise the once. */
142 if (gsasl_ctx == NULL) {
143 rc = gsasl_init(&gsasl_ctx);
144 if (rc != GSASL_OK) {
145 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
146 "couldn't initialise GNU SASL library: %s (%s)",
147 ablock->name, gsasl_strerror_name(rc), gsasl_strerror(rc));
149 gsasl_callback_set(gsasl_ctx, main_callback);
152 /* We don't need this except to log it for debugging. */
153 rc = gsasl_server_mechlist(gsasl_ctx, &p);
155 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
156 "failed to retrieve list of mechanisms: %s (%s)",
157 ablock->name, gsasl_strerror_name(rc), gsasl_strerror(rc));
158 HDEBUG(D_auth) debug_printf("GNU SASL supports: %s\n", p);
160 supported = gsasl_client_support_p(gsasl_ctx, CCS ob->server_mech);
162 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
163 "GNU SASL does not support mechanism \"%s\"",
164 ablock->name, ob->server_mech);
166 if ((ablock->server_condition == NULL) &&
167 (streqic(ob->server_mech, US"EXTERNAL") ||
168 streqic(ob->server_mech, US"ANONYMOUS") ||
169 streqic(ob->server_mech, US"PLAIN") ||
170 streqic(ob->server_mech, US"LOGIN")))
171 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
172 "Need server_condition for %s mechanism",
173 ablock->name, ob->server_mech);
175 /* This does *not* scale to new SASL mechanisms. Need a better way to ask
176 which properties will be needed. */
177 if ((ob->server_realm == NULL) &&
178 streqic(ob->server_mech, US"DIGEST-MD5"))
179 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
180 "Need server_realm for %s mechanism",
181 ablock->name, ob->server_mech);
183 /* At present, for mechanisms we don't panic on absence of server_condition;
184 need to figure out the most generically correct approach to deciding when
185 it's critical and when it isn't. Eg, for simple validation (PLAIN mechanism,
186 etc) it clearly is critical.
188 So don't activate without server_condition, this might be relaxed in the future.
190 if (ablock->server_condition != NULL) ablock->server = TRUE;
191 ablock->client = FALSE;
195 /* GNU SASL uses one top-level callback, registered at library level.
196 We dispatch to client and server functions instead. */
199 main_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop)
202 struct callback_exim_state *cb_state =
203 (struct callback_exim_state *)gsasl_session_hook_get(sctx);
206 debug_printf("GNU SASL Callback entered, prop=%d (loop prop=%d)\n",
207 prop, callback_loop);
209 if (cb_state == NULL) {
210 HDEBUG(D_auth) debug_printf(" not from our server/client processing.\n");
211 return GSASL_NO_CALLBACK;
214 if (callback_loop > 0) {
215 /* Most likely is that we were asked for property foo, and to
216 expand the string we asked for property bar to put into an auth
217 variable, but property bar is not supplied for this mechanism. */
219 debug_printf("Loop, asked for property %d while handling property %d\n",
220 prop, callback_loop);
221 return GSASL_NO_CALLBACK;
223 callback_loop = prop;
225 if (cb_state->currently == CURRENTLY_CLIENT)
226 rc = client_callback(ctx, sctx, prop, cb_state->ablock);
227 else if (cb_state->currently == CURRENTLY_SERVER)
228 rc = server_callback(ctx, sctx, prop, cb_state->ablock);
230 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
231 "unhandled callback state, bug in Exim", cb_state->ablock->name);
240 /*************************************************
241 * Server entry point *
242 *************************************************/
244 /* For interface, see auths/README */
247 auth_gsasl_server(auth_instance *ablock, uschar *initial_data)
250 char *to_send, *received;
251 Gsasl_session *sctx = NULL;
252 auth_gsasl_options_block *ob =
253 (auth_gsasl_options_block *)(ablock->options_block);
254 struct callback_exim_state cb_state;
255 int rc, auth_result, exim_error, exim_error_override;
258 debug_printf("GNU SASL: initialising session for %s, mechanism %s.\n",
259 ablock->name, ob->server_mech);
261 rc = gsasl_server_start(gsasl_ctx, CCS ob->server_mech, &sctx);
262 if (rc != GSASL_OK) {
263 auth_defer_msg = string_sprintf("GNU SASL: session start failure: %s (%s)",
264 gsasl_strerror_name(rc), gsasl_strerror(rc));
265 HDEBUG(D_auth) debug_printf("%s\n", auth_defer_msg);
268 /* Hereafter: gsasl_finish(sctx) please */
270 gsasl_session_hook_set(sctx, (void *)ablock);
271 cb_state.ablock = ablock;
272 cb_state.currently = CURRENTLY_SERVER;
273 gsasl_session_hook_set(sctx, (void *)&cb_state);
275 tmps = CS expand_string(ob->server_service);
276 gsasl_property_set(sctx, GSASL_SERVICE, tmps);
277 tmps = CS expand_string(ob->server_hostname);
278 gsasl_property_set(sctx, GSASL_HOSTNAME, tmps);
279 if (ob->server_realm) {
280 tmps = CS expand_string(ob->server_realm);
282 gsasl_property_set(sctx, GSASL_REALM, tmps);
285 /* We don't support protection layers. */
286 gsasl_property_set(sctx, GSASL_QOPS, "qop-auth");
288 if (tls_channelbinding_b64) {
289 /* Some auth mechanisms can ensure that both sides are talking withing the
290 same security context; for TLS, this means that even if a bad certificate
291 has been accepted, they remain MitM-proof because both sides must be within
292 the same negotiated session; if someone is terminating one session and
293 proxying data on within a second, authentication will fail.
295 We might not have this available, depending upon TLS implementation,
296 ciphersuite, phase of moon ...
298 If we do, it results in extra SASL mechanisms being available; here,
299 Exim's one-mechanism-per-authenticator potentially causes problems.
300 It depends upon how GNU SASL will implement the PLUS variants of GS2
301 and whether it automatically mandates a switch to the bound PLUS
302 if the data is available. Since default-on, despite being more secure,
303 would then result in mechanism name changes on a library update, we
304 have little choice but to default it off and let the admin choose to
307 if (ob->server_channelbinding) {
308 HDEBUG(D_auth) debug_printf("Auth %s: Enabling channel-binding\n",
310 gsasl_property_set(sctx, GSASL_CB_TLS_UNIQUE,
311 CCS tls_channelbinding_b64);
314 debug_printf("Auth %s: Not enabling channel-binding (data available)\n",
319 debug_printf("Auth %s: no channel-binding data available\n",
324 checked_server_condition = FALSE;
326 received = CS initial_data;
328 exim_error = exim_error_override = OK;
331 rc = gsasl_step64(sctx, received, &to_send);
336 goto STOP_INTERACTION;
339 case GSASL_NEEDS_MORE:
342 case GSASL_AUTHENTICATION_ERROR:
343 case GSASL_INTEGRITY_ERROR:
344 case GSASL_NO_AUTHID:
345 case GSASL_NO_ANONYMOUS_TOKEN:
346 case GSASL_NO_AUTHZID:
347 case GSASL_NO_PASSWORD:
348 case GSASL_NO_PASSCODE:
350 case GSASL_BASE64_ERROR:
351 HDEBUG(D_auth) debug_printf("GNU SASL permanent error: %s (%s)\n",
352 gsasl_strerror_name(rc), gsasl_strerror(rc));
353 log_write(0, LOG_REJECT, "%s authenticator (%s):\n "
354 "GNU SASL permanent failure: %s (%s)",
355 ablock->name, ob->server_mech,
356 gsasl_strerror_name(rc), gsasl_strerror(rc));
357 if (rc == GSASL_BASE64_ERROR)
358 exim_error_override = BAD64;
359 goto STOP_INTERACTION;
362 auth_defer_msg = string_sprintf("GNU SASL temporary error: %s (%s)",
363 gsasl_strerror_name(rc), gsasl_strerror(rc));
364 HDEBUG(D_auth) debug_printf("%s\n", auth_defer_msg);
365 exim_error_override = DEFER;
366 goto STOP_INTERACTION;
369 if ((rc == GSASL_NEEDS_MORE) ||
370 (to_send && *to_send))
372 auth_get_no64_data((uschar **)&received, US to_send);
380 break; /* handles * cancelled check */
382 } while (rc == GSASL_NEEDS_MORE);
389 /* Can return: OK DEFER FAIL CANCELLED BAD64 UNEXPECTED */
391 if (exim_error != OK)
394 if (auth_result != GSASL_OK) {
395 HDEBUG(D_auth) debug_printf("authentication returned %s (%s)\n",
396 gsasl_strerror_name(auth_result), gsasl_strerror(auth_result));
397 if (exim_error_override != OK)
398 return exim_error_override; /* might be DEFER */
399 if (sasl_error_should_defer) /* overriding auth failure SASL error */
404 /* Auth succeeded, check server_condition unless already done in callback */
405 return checked_server_condition ? OK : auth_check_serv_cond(ablock);
408 /* returns the GSASL status of expanding the Exim string given */
410 condition_check(auth_instance *ablock, uschar *label, uschar *condition_string)
414 exim_rc = auth_check_some_cond(ablock, label, condition_string, FAIL);
418 } else if (exim_rc == DEFER) {
419 sasl_error_should_defer = TRUE;
420 return GSASL_AUTHENTICATION_ERROR;
421 } else if (exim_rc == FAIL) {
422 return GSASL_AUTHENTICATION_ERROR;
425 log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator: "
426 "Unhandled return from checking %s: %d",
427 ablock->name, label, exim_rc);
429 return GSASL_AUTHENTICATION_ERROR;
433 server_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock)
437 int cbrc = GSASL_NO_CALLBACK;
439 auth_gsasl_options_block *ob =
440 (auth_gsasl_options_block *)(ablock->options_block);
443 debug_printf("GNU SASL callback %d for %s/%s as server\n",
444 prop, ablock->name, ablock->public_name);
446 for (i = 0; i < AUTH_VARS; i++) auth_vars[i] = NULL;
450 case GSASL_VALIDATE_SIMPLE:
451 /* GSASL_AUTHID, GSASL_AUTHZID, and GSASL_PASSWORD */
452 propval = US gsasl_property_fast(sctx, GSASL_AUTHID);
453 auth_vars[0] = expand_nstring[1] = propval ? propval : US"";
454 propval = US gsasl_property_fast(sctx, GSASL_AUTHZID);
455 auth_vars[1] = expand_nstring[2] = propval ? propval : US"";
456 propval = US gsasl_property_fast(sctx, GSASL_PASSWORD);
457 auth_vars[2] = expand_nstring[3] = propval ? propval : US"";
459 for (i = 1; i <= 3; ++i)
460 expand_nlength[i] = Ustrlen(expand_nstring[i]);
462 cbrc = condition_check(ablock, US"server_condition", ablock->server_condition);
463 checked_server_condition = TRUE;
466 case GSASL_VALIDATE_EXTERNAL:
467 if (ablock->server_condition == NULL) {
468 HDEBUG(D_auth) debug_printf("No server_condition supplied, to validate EXTERNAL.\n");
469 cbrc = GSASL_AUTHENTICATION_ERROR;
472 propval = US gsasl_property_fast(sctx, GSASL_AUTHZID);
473 /* We always set $auth1, even if only to empty string. */
474 auth_vars[0] = expand_nstring[1] = propval ? propval : US"";
475 expand_nlength[1] = Ustrlen(expand_nstring[1]);
478 cbrc = condition_check(ablock,
479 US"server_condition (EXTERNAL)", ablock->server_condition);
480 checked_server_condition = TRUE;
483 case GSASL_VALIDATE_ANONYMOUS:
484 if (ablock->server_condition == NULL) {
485 HDEBUG(D_auth) debug_printf("No server_condition supplied, to validate ANONYMOUS.\n");
486 cbrc = GSASL_AUTHENTICATION_ERROR;
489 propval = US gsasl_property_fast(sctx, GSASL_ANONYMOUS_TOKEN);
490 /* We always set $auth1, even if only to empty string. */
491 auth_vars[0] = expand_nstring[1] = propval ? propval : US"";
492 expand_nlength[1] = Ustrlen(expand_nstring[1]);
495 cbrc = condition_check(ablock,
496 US"server_condition (ANONYMOUS)", ablock->server_condition);
497 checked_server_condition = TRUE;
500 case GSASL_VALIDATE_GSSAPI:
501 /* GSASL_AUTHZID and GSASL_GSSAPI_DISPLAY_NAME
502 The display-name is authenticated as part of GSS, the authzid is claimed
503 by the SASL integration after authentication; protected against tampering
504 (if the SASL mechanism supports that, which Kerberos does) but is
505 unverified, same as normal for other mechanisms.
507 First coding, we had these values swapped, but for consistency and prior
508 to the first release of Exim with this authenticator, they've been
509 switched to match the ordering of GSASL_VALIDATE_SIMPLE. */
510 propval = US gsasl_property_fast(sctx, GSASL_GSSAPI_DISPLAY_NAME);
511 auth_vars[0] = expand_nstring[1] = propval ? propval : US"";
512 propval = US gsasl_property_fast(sctx, GSASL_AUTHZID);
513 auth_vars[1] = expand_nstring[2] = propval ? propval : US"";
515 for (i = 1; i <= 2; ++i)
516 expand_nlength[i] = Ustrlen(expand_nstring[i]);
518 /* In this one case, it perhaps makes sense to default back open?
519 But for consistency, let's just mandate server_condition here too. */
520 cbrc = condition_check(ablock,
521 US"server_condition (GSSAPI family)", ablock->server_condition);
522 checked_server_condition = TRUE;
526 /* DIGEST-MD5: GSASL_AUTHID, GSASL_AUTHZID and GSASL_REALM
527 CRAM-MD5: GSASL_AUTHID
528 PLAIN: GSASL_AUTHID and GSASL_AUTHZID
531 if (ob->server_scram_iter) {
532 tmps = CS expand_string(ob->server_scram_iter);
533 gsasl_property_set(sctx, GSASL_SCRAM_ITER, tmps);
535 if (ob->server_scram_salt) {
536 tmps = CS expand_string(ob->server_scram_salt);
537 gsasl_property_set(sctx, GSASL_SCRAM_SALT, tmps);
539 /* Asking for GSASL_AUTHZID calls back into us if we use
540 gsasl_property_get(), thus the use of gsasl_property_fast().
541 Do we really want to hardcode limits per mechanism? What happens when
542 a new mechanism is added to the library. It *shouldn't* result in us
543 needing to add more glue, since avoiding that is a large part of the
545 propval = US gsasl_property_fast(sctx, GSASL_AUTHID);
546 auth_vars[0] = expand_nstring[1] = propval ? propval : US"";
547 propval = US gsasl_property_fast(sctx, GSASL_AUTHZID);
548 auth_vars[1] = expand_nstring[2] = propval ? propval : US"";
549 propval = US gsasl_property_fast(sctx, GSASL_REALM);
550 auth_vars[2] = expand_nstring[3] = propval ? propval : US"";
552 for (i = 1; i <= 3; ++i)
553 expand_nlength[i] = Ustrlen(expand_nstring[i]);
555 tmps = CS expand_string(ob->server_password);
557 sasl_error_should_defer = f.expand_string_forcedfail ? FALSE : TRUE;
558 HDEBUG(D_auth) debug_printf("server_password expansion failed, so "
559 "can't tell GNU SASL library the password for %s\n", auth_vars[0]);
560 return GSASL_AUTHENTICATION_ERROR;
562 gsasl_property_set(sctx, GSASL_PASSWORD, tmps);
563 /* This is inadequate; don't think Exim's store stacks are geared
564 for memory wiping, so expanding strings will leave stuff laying around.
565 But no need to compound the problem, so get rid of the one we can. */
566 memset(tmps, '\0', strlen(tmps));
571 HDEBUG(D_auth) debug_printf("Unrecognised callback: %d\n", prop);
572 cbrc = GSASL_NO_CALLBACK;
575 HDEBUG(D_auth) debug_printf("Returning %s (%s)\n",
576 gsasl_strerror_name(cbrc), gsasl_strerror(cbrc));
582 /*************************************************
583 * Client entry point *
584 *************************************************/
586 /* For interface, see auths/README */
590 auth_instance *ablock, /* authenticator block */
591 smtp_inblock *inblock, /* connection inblock */
592 smtp_outblock *outblock, /* connection outblock */
593 int timeout, /* command timeout */
594 uschar *buffer, /* buffer for reading response */
595 int buffsize) /* size of buffer */
598 debug_printf("Client side NOT IMPLEMENTED: you should not see this!\n");
599 /* NOT IMPLEMENTED */
604 client_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock)
606 int cbrc = GSASL_NO_CALLBACK;
608 debug_printf("GNU SASL callback %d for %s/%s as client\n",
609 prop, ablock->name, ablock->public_name);
612 debug_printf("Client side NOT IMPLEMENTED: you should not see this!\n");
617 /*************************************************
619 *************************************************/
622 auth_gsasl_version_report(FILE *f)
625 runtime = gsasl_check_version(NULL);
626 fprintf(f, "Library version: GNU SASL: Compile: %s\n"
628 GSASL_VERSION, runtime);
631 #endif /*!MACRO_PREDEF*/
632 #endif /* AUTH_GSASL */
634 /* End of gsasl_exim.c */