Adding upstream version 4.94.2.upstream/4.94.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 982 insertions, 0 deletions

diff --git a/src/auths/gsasl_exim.c b/src/auths/gsasl_exim.c
new file mode 100644
index 0000000..a3aaf1f
--- /dev/null
+++ b/src/auths/gsasl_exim.c
@@ -0,0 +1,982 @@
+/*************************************************
+*     Exim - an Internet mail transport agent    *
+*************************************************/
+
+/* Copyright (c) The Exim Maintainers 2019-2020 */
+/* Copyright (c) University of Cambridge 1995 - 2018 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+/* Copyright (c) Twitter Inc 2012
+   Author: Phil Pennock <pdp@exim.org> */
+/* Copyright (c) Phil Pennock 2012 */
+
+/* Interface to GNU SASL library for generic authentication. */
+
+/* Trade-offs:
+
+GNU SASL does not provide authentication data itself, so we have to expose
+that decision to configuration.  For some mechanisms, we need to act much
+like plaintext.  For others, we only need to be able to provide some
+evaluated data on demand.  There's no abstracted way (ie, without hardcoding
+knowledge of authenticators here) to know which need what properties; we
+can't query a session or the library for "we will need these for mechanism X".
+
+So: we always require server_condition, even if sometimes it will just be
+set as "yes".  We do provide a number of other hooks, which might not make
+sense in all contexts.  For some, we can do checks at init time.
+*/
+
+#include "../exim.h"
+#define CHANNELBIND_HACK
+
+#ifndef AUTH_GSASL
+/* dummy function to satisfy compilers when we link in an "empty" file. */
+static void dummy(int x);
+static void dummy2(int x) { dummy(x-1); }
+static void dummy(int x) { dummy2(x-1); }
+#else
+
+#include <gsasl.h>
+#include "gsasl_exim.h"
+
+
+#if GSASL_VERSION_MINOR >= 9
+# define EXIM_GSASL_HAVE_SCRAM_SHA_256
+
+# if GSASL_VERSION_PATCH >= 1
+#  define EXIM_GSASL_SCRAM_S_KEY
+# endif
+#endif
+
+
+/* Authenticator-specific options. */
+/* I did have server_*_condition options for various mechanisms, but since
+we only ever handle one mechanism at a time, I didn't see the point in keeping
+that.  In case someone sees a point, I've left the condition_check() API
+alone. */
+#define LOFF(field) OPT_OFF(auth_gsasl_options_block, field)
+
+optionlist auth_gsasl_options[] = {
+  { "client_authz",		opt_stringptr,	LOFF(client_authz) },
+  { "client_channelbinding",	opt_bool,	LOFF(client_channelbinding) },
+  { "client_password",		opt_stringptr,	LOFF(client_password) },
+  { "client_spassword",		opt_stringptr,	LOFF(client_spassword) },
+  { "client_username",		opt_stringptr,	LOFF(client_username) },
+
+  { "server_channelbinding",	opt_bool,	LOFF(server_channelbinding) },
+  { "server_hostname",		opt_stringptr,	LOFF(server_hostname) },
+#ifdef EXIM_GSASL_SCRAM_S_KEY
+  { "server_key",		opt_stringptr,	LOFF(server_key) },
+#endif
+  { "server_mech",		opt_stringptr,	LOFF(server_mech) },
+  { "server_password",		opt_stringptr,	LOFF(server_password) },
+  { "server_realm",		opt_stringptr,	LOFF(server_realm) },
+  { "server_scram_iter",	opt_stringptr,	LOFF(server_scram_iter) },
+  { "server_scram_salt",	opt_stringptr,	LOFF(server_scram_salt) },
+#ifdef EXIM_GSASL_SCRAM_S_KEY
+  { "server_skey",		opt_stringptr,	LOFF(server_s_key) },
+#endif
+  { "server_service",		opt_stringptr,	LOFF(server_service) }
+};
+
+int auth_gsasl_options_count =
+  sizeof(auth_gsasl_options)/sizeof(optionlist);
+
+/* Defaults for the authenticator-specific options. */
+auth_gsasl_options_block auth_gsasl_option_defaults = {
+  .server_service = US"smtp",
+  .server_hostname = US"$primary_hostname",
+  .server_scram_iter = US"4096",
+  /* all others zero/null */
+};
+
+
+#ifdef MACRO_PREDEF
+# include "../macro_predef.h"
+
+/* Dummy values */
+void auth_gsasl_init(auth_instance *ablock) {}
+int auth_gsasl_server(auth_instance *ablock, uschar *data) {return 0;}
+int auth_gsasl_client(auth_instance *ablock, void * sx,
+  int timeout, uschar *buffer, int buffsize) {return 0;}
+void auth_gsasl_version_report(FILE *f) {}
+
+void
+auth_gsasl_macros(void)
+{
+# ifdef EXIM_GSASL_HAVE_SCRAM_SHA_256
+  builtin_macro_create(US"_HAVE_AUTH_GSASL_SCRAM_SHA_256");
+# endif
+# ifdef EXIM_GSASL_SCRAM_S_KEY
+  builtin_macro_create(US"_HAVE_AUTH_GSASL_SCRAM_S_KEY");
+# endif
+}
+
+#else   /*!MACRO_PREDEF*/
+
+
+
+/* "Globals" for managing the gsasl interface. */
+
+static Gsasl *gsasl_ctx = NULL;
+static int
+  main_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop);
+static int
+  server_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock);
+static int
+  client_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock);
+
+static BOOL sasl_error_should_defer = FALSE;
+static Gsasl_property callback_loop = 0;
+static BOOL checked_server_condition = FALSE;
+
+enum { CURRENTLY_SERVER = 1, CURRENTLY_CLIENT = 2 };
+
+struct callback_exim_state {
+  auth_instance *ablock;
+  int currently;
+};
+
+
+/*************************************************
+*          Initialization entry point            *
+*************************************************/
+
+/* Called for each instance, after its options have been read, to
+enable consistency checks to be done, or anything else that needs
+to be set up. */
+
+void
+auth_gsasl_init(auth_instance *ablock)
+{
+static char * once = NULL;
+int rc;
+auth_gsasl_options_block *ob =
+  (auth_gsasl_options_block *)(ablock->options_block);
+
+/* As per existing Cyrus glue, use the authenticator's public name as
+the default for the mechanism name; we don't handle multiple mechanisms
+in one authenticator, but the same driver can be used multiple times. */
+
+if (!ob->server_mech)
+  ob->server_mech = string_copy(ablock->public_name);
+
+/* Can get multiple session contexts from one library context, so just
+initialise the once. */
+
+if (!gsasl_ctx)
+  {
+  if ((rc = gsasl_init(&gsasl_ctx)) != GSASL_OK)
+    log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator:  "
+	      "couldn't initialise GNU SASL library: %s (%s)",
+	      ablock->name, gsasl_strerror_name(rc), gsasl_strerror(rc));
+
+  gsasl_callback_set(gsasl_ctx, main_callback);
+  }
+
+/* We don't need this except to log it for debugging. */
+
+HDEBUG(D_auth) if (!once)
+  {
+  if ((rc = gsasl_server_mechlist(gsasl_ctx, &once)) != GSASL_OK)
+    log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator:  "
+	      "failed to retrieve list of mechanisms: %s (%s)",
+	      ablock->name,  gsasl_strerror_name(rc), gsasl_strerror(rc));
+
+  debug_printf("GNU SASL supports: %s\n", once);
+  }
+
+if (!gsasl_client_support_p(gsasl_ctx, CCS ob->server_mech))
+  log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator:  "
+	    "GNU SASL does not support mechanism \"%s\"",
+	    ablock->name, ob->server_mech);
+
+ablock->server = TRUE;
+
+if (  !ablock->server_condition
+   && (  streqic(ob->server_mech, US"EXTERNAL")
+      || streqic(ob->server_mech, US"ANONYMOUS")
+      || streqic(ob->server_mech, US"PLAIN")
+      || streqic(ob->server_mech, US"LOGIN")
+   )  )
+  {
+  ablock->server = FALSE;
+  HDEBUG(D_auth) debug_printf("%s authenticator:  "
+	    "Need server_condition for %s mechanism\n",
+	    ablock->name, ob->server_mech);
+  }
+
+/* This does *not* scale to new SASL mechanisms.  Need a better way to ask
+which properties will be needed. */
+
+if (  !ob->server_realm
+   && streqic(ob->server_mech, US"DIGEST-MD5"))
+  {
+  ablock->server = FALSE;
+  HDEBUG(D_auth) debug_printf("%s authenticator:  "
+	    "Need server_realm for %s mechanism\n",
+	    ablock->name, ob->server_mech);
+  }
+
+/* At present, for mechanisms we don't panic on absence of server_condition;
+need to figure out the most generically correct approach to deciding when
+it's critical and when it isn't.  Eg, for simple validation (PLAIN mechanism,
+etc) it clearly is critical.
+*/
+
+ablock->client = ob->client_username && ob->client_password;
+}
+
+
+/* GNU SASL uses one top-level callback, registered at library level.
+We dispatch to client and server functions instead. */
+
+static int
+main_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop)
+{
+int rc = 0;
+struct callback_exim_state *cb_state =
+  (struct callback_exim_state *)gsasl_session_hook_get(sctx);
+
+if (!cb_state)
+  {
+  HDEBUG(D_auth) debug_printf("gsasl callback (%d) not from our server/client processing\n", prop);
+#ifdef CHANNELBIND_HACK
+  if (prop == GSASL_CB_TLS_UNIQUE)
+    {
+    uschar * s;
+    if ((s = gsasl_callback_hook_get(ctx)))
+      {
+      HDEBUG(D_auth) debug_printf("GSASL_CB_TLS_UNIQUE from ctx hook\n");
+      gsasl_property_set(sctx, GSASL_CB_TLS_UNIQUE, CS s);
+      }
+    else
+      {
+      HDEBUG(D_auth) debug_printf("GSASL_CB_TLS_UNIQUE!  dummy for now\n");
+      gsasl_property_set(sctx, GSASL_CB_TLS_UNIQUE, "");
+      }
+    return GSASL_OK;
+    }
+#endif
+  return GSASL_NO_CALLBACK;
+  }
+
+HDEBUG(D_auth)
+  debug_printf("GNU SASL Callback entered, prop=%d (loop prop=%d)\n",
+      prop, callback_loop);
+
+if (callback_loop > 0)
+  {
+  /* Most likely is that we were asked for property FOO, and to
+  expand the string we asked for property BAR to put into an auth
+  variable, but property BAR is not supplied for this mechanism. */
+  HDEBUG(D_auth)
+    debug_printf("Loop, asked for property %d while handling property %d\n",
+	prop, callback_loop);
+  return GSASL_NO_CALLBACK;
+  }
+callback_loop = prop;
+
+if (cb_state->currently == CURRENTLY_CLIENT)
+  rc = client_callback(ctx, sctx, prop, cb_state->ablock);
+else if (cb_state->currently == CURRENTLY_SERVER)
+  rc = server_callback(ctx, sctx, prop, cb_state->ablock);
+else
+  log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator:  "
+      "unhandled callback state, bug in Exim", cb_state->ablock->name);
+  /* NOTREACHED */
+
+callback_loop = 0;
+return rc;
+}
+
+
+/*************************************************
+*             Debug service function             *
+*************************************************/
+static const uschar * 
+gsasl_prop_code_to_name(Gsasl_property prop)
+{
+switch (prop)
+  {
+  case GSASL_AUTHID: return US"AUTHID";
+  case GSASL_AUTHZID: return US"AUTHZID";
+  case GSASL_PASSWORD: return US"PASSWORD";
+  case GSASL_ANONYMOUS_TOKEN: return US"ANONYMOUS_TOKEN";
+  case GSASL_SERVICE: return US"SERVICE";
+  case GSASL_HOSTNAME: return US"HOSTNAME";
+  case GSASL_GSSAPI_DISPLAY_NAME: return US"GSSAPI_DISPLAY_NAME";
+  case GSASL_PASSCODE: return US"PASSCODE";
+  case GSASL_SUGGESTED_PIN: return US"SUGGESTED_PIN";
+  case GSASL_PIN: return US"PIN";
+  case GSASL_REALM: return US"REALM";
+  case GSASL_DIGEST_MD5_HASHED_PASSWORD: return US"DIGEST_MD5_HASHED_PASSWORD";
+  case GSASL_QOPS: return US"QOPS";
+  case GSASL_QOP: return US"QOP";
+  case GSASL_SCRAM_ITER: return US"SCRAM_ITER";
+  case GSASL_SCRAM_SALT: return US"SCRAM_SALT";
+  case GSASL_SCRAM_SALTED_PASSWORD: return US"SCRAM_SALTED_PASSWORD";
+#ifdef EXIM_GSASL_SCRAM_S_KEY
+  case GSASL_SCRAM_STOREDKEY: return US"SCRAM_STOREDKEY";
+  case GSASL_SCRAM_SERVERKEY: return US"SCRAM_SERVERKEY";
+#endif
+  case GSASL_CB_TLS_UNIQUE: return US"CB_TLS_UNIQUE";
+  case GSASL_SAML20_IDP_IDENTIFIER: return US"SAML20_IDP_IDENTIFIER";
+  case GSASL_SAML20_REDIRECT_URL: return US"SAML20_REDIRECT_URL";
+  case GSASL_OPENID20_REDIRECT_URL: return US"OPENID20_REDIRECT_URL";
+  case GSASL_OPENID20_OUTCOME_DATA: return US"OPENID20_OUTCOME_DATA";
+  case GSASL_SAML20_AUTHENTICATE_IN_BROWSER: return US"SAML20_AUTHENTICATE_IN_BROWSER";
+  case GSASL_OPENID20_AUTHENTICATE_IN_BROWSER: return US"OPENID20_AUTHENTICATE_IN_BROWSER";
+#ifdef EXIM_GSASL_SCRAM_S_KEY
+  case GSASL_SCRAM_CLIENTKEY: return US"SCRAM_CLIENTKEY";
+#endif
+  case GSASL_VALIDATE_SIMPLE: return US"VALIDATE_SIMPLE";
+  case GSASL_VALIDATE_EXTERNAL: return US"VALIDATE_EXTERNAL";
+  case GSASL_VALIDATE_ANONYMOUS: return US"VALIDATE_ANONYMOUS";
+  case GSASL_VALIDATE_GSSAPI: return US"VALIDATE_GSSAPI";
+  case GSASL_VALIDATE_SECURID: return US"VALIDATE_SECURID";
+  case GSASL_VALIDATE_SAML20: return US"VALIDATE_SAML20";
+  case GSASL_VALIDATE_OPENID20: return US"VALIDATE_OPENID20";
+  }
+return CUS string_sprintf("(unknown prop: %d)", (int)prop);
+}
+
+/*************************************************
+*             Server entry point                 *
+*************************************************/
+
+/* For interface, see auths/README */
+
+int
+auth_gsasl_server(auth_instance *ablock, uschar *initial_data)
+{
+char *tmps;
+char *to_send, *received;
+Gsasl_session *sctx = NULL;
+auth_gsasl_options_block *ob =
+  (auth_gsasl_options_block *)(ablock->options_block);
+struct callback_exim_state cb_state;
+int rc, auth_result, exim_error, exim_error_override;
+
+HDEBUG(D_auth)
+  debug_printf("GNU SASL: initialising session for %s, mechanism %s\n",
+      ablock->name, ob->server_mech);
+
+#ifndef DISABLE_TLS
+if (tls_in.channelbinding && ob->server_channelbinding)
+  {
+# ifdef EXPERIMENTAL_TLS_RESUME
+  if (!tls_in.ext_master_secret && tls_in.resumption == RESUME_USED)
+    {		/* per RFC 7677 section 4 */
+    HDEBUG(D_auth) debug_printf(
+      "channel binding not usable on resumed TLS without extended-master-secret");
+    return FAIL;
+    }
+# endif
+# ifdef CHANNELBIND_HACK
+/* This is a gross hack to get around the library a) requiring that
+c-b was already set, at the _start() call, and b) caching a b64'd
+version of the binding then which it never updates. */
+
+  gsasl_callback_hook_set(gsasl_ctx, tls_in.channelbinding);
+# endif
+  }
+#endif
+
+if ((rc = gsasl_server_start(gsasl_ctx, CCS ob->server_mech, &sctx)) != GSASL_OK)
+  {
+  auth_defer_msg = string_sprintf("GNU SASL: session start failure: %s (%s)",
+      gsasl_strerror_name(rc), gsasl_strerror(rc));
+  HDEBUG(D_auth) debug_printf("%s\n", auth_defer_msg);
+  return DEFER;
+  }
+/* Hereafter: gsasl_finish(sctx) please */
+
+cb_state.ablock = ablock;
+cb_state.currently = CURRENTLY_SERVER;
+gsasl_session_hook_set(sctx, &cb_state);
+
+tmps = CS expand_string(ob->server_service);
+gsasl_property_set(sctx, GSASL_SERVICE, tmps);
+tmps = CS expand_string(ob->server_hostname);
+gsasl_property_set(sctx, GSASL_HOSTNAME, tmps);
+if (ob->server_realm)
+  {
+  tmps = CS expand_string(ob->server_realm);
+  if (tmps && *tmps)
+    gsasl_property_set(sctx, GSASL_REALM, tmps);
+  }
+/* We don't support protection layers. */
+gsasl_property_set(sctx, GSASL_QOPS, "qop-auth");
+
+#ifndef DISABLE_TLS
+if (tls_in.channelbinding)
+  {
+  /* Some auth mechanisms can ensure that both sides are talking withing the
+  same security context; for TLS, this means that even if a bad certificate
+  has been accepted, they remain MitM-proof because both sides must be within
+  the same negotiated session; if someone is terminating one session and
+  proxying data on within a second, authentication will fail.
+
+  We might not have this available, depending upon TLS implementation,
+  ciphersuite, phase of moon ...
+
+  If we do, it results in extra SASL mechanisms being available; here,
+  Exim's one-mechanism-per-authenticator potentially causes problems.
+  It depends upon how GNU SASL will implement the PLUS variants of GS2
+  and whether it automatically mandates a switch to the bound PLUS
+  if the data is available.  Since default-on, despite being more secure,
+  would then result in mechanism name changes on a library update, we
+  have little choice but to default it off and let the admin choose to
+  enable it.  *sigh*
+  */
+  if (ob->server_channelbinding)
+    {
+    HDEBUG(D_auth) debug_printf("Auth %s: Enabling channel-binding\n",
+	ablock->name);
+# ifndef CHANNELBIND_HACK
+    gsasl_property_set(sctx, GSASL_CB_TLS_UNIQUE, CCS tls_in.channelbinding);
+# endif
+    }
+  else
+    HDEBUG(D_auth)
+      debug_printf("Auth %s: Not enabling channel-binding (data available)\n",
+	  ablock->name);
+  }
+else
+  HDEBUG(D_auth)
+    debug_printf("Auth %s: no channel-binding data available\n",
+	ablock->name);
+#endif
+
+checked_server_condition = FALSE;
+
+received = CS initial_data;
+to_send = NULL;
+exim_error = exim_error_override = OK;
+
+do {
+  switch (rc = gsasl_step64(sctx, received, &to_send))
+    {
+    case GSASL_OK:
+      if (!to_send)
+	goto STOP_INTERACTION;
+      break;
+
+    case GSASL_NEEDS_MORE:
+      break;
+
+    case GSASL_AUTHENTICATION_ERROR:
+    case GSASL_INTEGRITY_ERROR:
+    case GSASL_NO_AUTHID:
+    case GSASL_NO_ANONYMOUS_TOKEN:
+    case GSASL_NO_AUTHZID:
+    case GSASL_NO_PASSWORD:
+    case GSASL_NO_PASSCODE:
+    case GSASL_NO_PIN:
+    case GSASL_BASE64_ERROR:
+      HDEBUG(D_auth) debug_printf("GNU SASL permanent error: %s (%s)\n",
+	  gsasl_strerror_name(rc), gsasl_strerror(rc));
+      log_write(0, LOG_REJECT, "%s authenticator (%s):\n  "
+	  "GNU SASL permanent failure: %s (%s)",
+	  ablock->name, ob->server_mech,
+	  gsasl_strerror_name(rc), gsasl_strerror(rc));
+      if (rc == GSASL_BASE64_ERROR)
+	exim_error_override = BAD64;
+      goto STOP_INTERACTION;
+
+    default:
+      auth_defer_msg = string_sprintf("GNU SASL temporary error: %s (%s)",
+	  gsasl_strerror_name(rc), gsasl_strerror(rc));
+      HDEBUG(D_auth) debug_printf("%s\n", auth_defer_msg);
+      exim_error_override = DEFER;
+      goto STOP_INTERACTION;
+    }
+
+  /*XXX having our caller send the final smtp "235" is unfortunate; wastes a roundtrip */
+  if ((rc == GSASL_NEEDS_MORE) || (to_send && *to_send))
+    exim_error = auth_get_no64_data(USS &received, US to_send);
+
+  if (to_send)
+    {
+    free(to_send);
+    to_send = NULL;
+    }
+
+  if (exim_error)
+    break; /* handles * cancelled check */
+
+  } while (rc == GSASL_NEEDS_MORE);
+
+STOP_INTERACTION:
+auth_result = rc;
+
+HDEBUG(D_auth)
+  {
+  const uschar * s;
+  if ((s = CUS gsasl_property_fast(sctx, GSASL_SCRAM_ITER)))
+    debug_printf(" - itercnt:   '%s'\n", s);
+  if ((s = CUS gsasl_property_fast(sctx, GSASL_SCRAM_SALT)))
+    debug_printf(" - salt:      '%s'\n", s);
+#ifdef EXIM_GSASL_SCRAM_S_KEY
+  if ((s = CUS gsasl_property_fast(sctx, GSASL_SCRAM_SERVERKEY)))
+    debug_printf(" - ServerKey: '%s'\n", s);
+  if ((s = CUS gsasl_property_fast(sctx, GSASL_SCRAM_STOREDKEY)))
+    debug_printf(" - StoredKey: '%s'\n", s);
+#endif
+  }
+
+gsasl_finish(sctx);
+
+/* Can return: OK DEFER FAIL CANCELLED BAD64 UNEXPECTED */
+
+if (exim_error != OK)
+  return exim_error;
+
+if (auth_result != GSASL_OK)
+  {
+  HDEBUG(D_auth) debug_printf("authentication returned %s (%s)\n",
+      gsasl_strerror_name(auth_result), gsasl_strerror(auth_result));
+  if (exim_error_override != OK)
+    return exim_error_override; /* might be DEFER */
+  if (sasl_error_should_defer) /* overriding auth failure SASL error */
+    return DEFER;
+  return FAIL;
+  }
+
+/* Auth succeeded, check server_condition unless already done in callback */
+return checked_server_condition ? OK : auth_check_serv_cond(ablock);
+}
+
+
+/* returns the GSASL status of expanding the Exim string given */
+static int
+condition_check(auth_instance *ablock, uschar *label, uschar *condition_string)
+{
+int exim_rc = auth_check_some_cond(ablock, label, condition_string, FAIL);
+switch (exim_rc)
+  {
+  case OK:	return GSASL_OK;
+  case DEFER:	sasl_error_should_defer = TRUE;
+		return GSASL_AUTHENTICATION_ERROR;
+  case FAIL:	return GSASL_AUTHENTICATION_ERROR;
+  default:	log_write(0, LOG_PANIC_DIE|LOG_CONFIG_FOR, "%s authenticator:  "
+		  "Unhandled return from checking %s: %d",
+		  ablock->name, label, exim_rc);
+  }
+
+/* NOTREACHED */
+return GSASL_AUTHENTICATION_ERROR;
+}
+
+
+static void
+set_exim_authvar_from_prop(Gsasl_session * sctx, Gsasl_property prop)
+{
+uschar * propval = US gsasl_property_fast(sctx, prop);
+int i = expand_nmax, j = i + 1;
+propval = propval ? string_copy(propval) : US"";
+auth_vars[i] = expand_nstring[j] = propval;
+expand_nlength[j] = Ustrlen(propval);
+expand_nmax = j;
+}
+
+static void
+set_exim_authvars_from_a_az_r_props(Gsasl_session * sctx)
+{
+if (expand_nmax > 0 ) return;
+
+/* Asking for GSASL_AUTHZID calls back into us if we use
+gsasl_property_get(), thus the use of gsasl_property_fast().
+Do we really want to hardcode limits per mechanism?  What happens when
+a new mechanism is added to the library.  It *shouldn't* result in us
+needing to add more glue, since avoiding that is a large part of the
+point of SASL. */
+
+set_exim_authvar_from_prop(sctx, GSASL_AUTHID);
+set_exim_authvar_from_prop(sctx, GSASL_AUTHZID);
+set_exim_authvar_from_prop(sctx, GSASL_REALM);
+}
+
+
+static int
+prop_from_option(Gsasl_session * sctx, Gsasl_property prop,
+  const uschar * option)
+{
+HDEBUG(D_auth) debug_printf(" %s\n", gsasl_prop_code_to_name(prop));
+if (option)
+  {
+  set_exim_authvars_from_a_az_r_props(sctx);
+  option = expand_cstring(option);
+  HDEBUG(D_auth) debug_printf("  '%s'\n", option);
+  if (*option)
+    gsasl_property_set(sctx, prop, CCS option);
+  return GSASL_OK;
+  }
+HDEBUG(D_auth) debug_printf("  option not set\n");
+return GSASL_NO_CALLBACK;
+}
+
+static int
+server_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop,
+  auth_instance *ablock)
+{
+char *tmps;
+uschar *s, *propval;
+int cbrc = GSASL_NO_CALLBACK;
+auth_gsasl_options_block *ob =
+  (auth_gsasl_options_block *)(ablock->options_block);
+
+HDEBUG(D_auth) debug_printf("GNU SASL callback %s for %s/%s as server\n",
+	    gsasl_prop_code_to_name(prop), ablock->name, ablock->public_name);
+
+for (int i = 0; i < AUTH_VARS; i++) auth_vars[i] = NULL;
+expand_nmax = 0;
+
+switch (prop)
+  {
+  case GSASL_VALIDATE_SIMPLE:
+    /* GSASL_AUTHID, GSASL_AUTHZID, and GSASL_PASSWORD */
+    set_exim_authvar_from_prop(sctx, GSASL_AUTHID);
+    set_exim_authvar_from_prop(sctx, GSASL_AUTHZID);
+    set_exim_authvar_from_prop(sctx, GSASL_PASSWORD);
+
+    cbrc = condition_check(ablock, US"server_condition", ablock->server_condition);
+    checked_server_condition = TRUE;
+    break;
+
+  case GSASL_VALIDATE_EXTERNAL:
+    if (!ablock->server_condition)
+      {
+      HDEBUG(D_auth) debug_printf("No server_condition supplied, to validate EXTERNAL\n");
+      cbrc = GSASL_AUTHENTICATION_ERROR;
+      break;
+      }
+    set_exim_authvar_from_prop(sctx, GSASL_AUTHZID);
+
+    cbrc = condition_check(ablock,
+	US"server_condition (EXTERNAL)", ablock->server_condition);
+    checked_server_condition = TRUE;
+    break;
+
+  case GSASL_VALIDATE_ANONYMOUS:
+    if (!ablock->server_condition)
+      {
+      HDEBUG(D_auth) debug_printf("No server_condition supplied, to validate ANONYMOUS\n");
+      cbrc = GSASL_AUTHENTICATION_ERROR;
+      break;
+      }
+    set_exim_authvar_from_prop(sctx, GSASL_ANONYMOUS_TOKEN);
+
+    cbrc = condition_check(ablock,
+	US"server_condition (ANONYMOUS)", ablock->server_condition);
+    checked_server_condition = TRUE;
+    break;
+
+  case GSASL_VALIDATE_GSSAPI:
+    /* GSASL_AUTHZID and GSASL_GSSAPI_DISPLAY_NAME
+    The display-name is authenticated as part of GSS, the authzid is claimed
+    by the SASL integration after authentication; protected against tampering
+    (if the SASL mechanism supports that, which Kerberos does) but is
+    unverified, same as normal for other mechanisms.
+     First coding, we had these values swapped, but for consistency and prior
+    to the first release of Exim with this authenticator, they've been
+    switched to match the ordering of GSASL_VALIDATE_SIMPLE. */
+
+    set_exim_authvar_from_prop(sctx, GSASL_GSSAPI_DISPLAY_NAME);
+    set_exim_authvar_from_prop(sctx, GSASL_AUTHZID);
+
+    /* In this one case, it perhaps makes sense to default back open?
+    But for consistency, let's just mandate server_condition here too. */
+
+    cbrc = condition_check(ablock,
+	US"server_condition (GSSAPI family)", ablock->server_condition);
+    checked_server_condition = TRUE;
+    break;
+
+  case GSASL_SCRAM_ITER:
+    cbrc = prop_from_option(sctx, prop, ob->server_scram_iter);
+    break;
+
+  case GSASL_SCRAM_SALT:
+    cbrc = prop_from_option(sctx, prop, ob->server_scram_salt);
+    break;
+
+#ifdef EXIM_GSASL_SCRAM_S_KEY
+  case GSASL_SCRAM_STOREDKEY:
+    cbrc = prop_from_option(sctx, prop, ob->server_s_key);
+    break;
+
+  case GSASL_SCRAM_SERVERKEY:
+    cbrc = prop_from_option(sctx, prop, ob->server_key);
+    break;
+#endif
+
+  case GSASL_PASSWORD:
+    /* SCRAM-*: GSASL_AUTHID, GSASL_AUTHZID and GSASL_REALM
+       DIGEST-MD5: GSASL_AUTHID, GSASL_AUTHZID and GSASL_REALM
+       CRAM-MD5: GSASL_AUTHID
+       PLAIN: GSASL_AUTHID and GSASL_AUTHZID
+       LOGIN: GSASL_AUTHID
+     */
+    set_exim_authvars_from_a_az_r_props(sctx);
+
+    if (!(s = ob->server_password))
+      {
+      HDEBUG(D_auth) debug_printf("option not set\n");
+      break;
+      }
+    if (!(tmps = CS expand_string(s)))
+      {
+      sasl_error_should_defer = !f.expand_string_forcedfail;
+      HDEBUG(D_auth) debug_printf("server_password expansion failed, so "
+	  "can't tell GNU SASL library the password for %s\n", auth_vars[0]);
+      return GSASL_AUTHENTICATION_ERROR;
+      }
+    HDEBUG(D_auth) debug_printf("  set\n");
+    gsasl_property_set(sctx, GSASL_PASSWORD, tmps);
+
+    /* This is inadequate; don't think Exim's store stacks are geared
+    for memory wiping, so expanding strings will leave stuff laying around.
+    But no need to compound the problem, so get rid of the one we can. */
+
+    memset(tmps, '\0', strlen(tmps));
+    cbrc = GSASL_OK;
+    break;
+
+  default:
+    HDEBUG(D_auth) debug_printf(" Unrecognised callback: %d\n", prop);
+    cbrc = GSASL_NO_CALLBACK;
+  }
+
+HDEBUG(D_auth) debug_printf("Returning %s (%s)\n",
+    gsasl_strerror_name(cbrc), gsasl_strerror(cbrc));
+
+return cbrc;
+}
+
+
+/******************************************************************************/
+
+#define PROP_OPTIONAL	BIT(0)
+
+static BOOL
+set_client_prop(Gsasl_session * sctx, Gsasl_property prop, uschar * val,
+  unsigned flags, uschar * buffer, int buffsize)
+{
+uschar * s;
+int rc;
+
+if (!val) return !!(flags & PROP_OPTIONAL);
+if (!(s = expand_string(val)) || !(flags & PROP_OPTIONAL) && !*s)
+  {
+  string_format(buffer, buffsize, "%s", expand_string_message);
+  return FALSE;
+  }
+if (*s)
+  {
+  HDEBUG(D_auth) debug_printf("%s: set %s = '%s'\n", __FUNCTION__,
+    gsasl_prop_code_to_name(prop), s);
+  gsasl_property_set(sctx, prop, CS s);
+  }
+
+return TRUE;
+}
+
+/*************************************************
+*              Client entry point                *
+*************************************************/
+
+/* For interface, see auths/README */
+
+int
+auth_gsasl_client(
+  auth_instance *ablock,		/* authenticator block */
+  void * sx,				/* connection */
+  int timeout,				/* command timeout */
+  uschar *buffer,			/* buffer for reading response */
+  int buffsize)				/* size of buffer */
+{
+auth_gsasl_options_block *ob =
+  (auth_gsasl_options_block *)(ablock->options_block);
+Gsasl_session * sctx = NULL;
+struct callback_exim_state cb_state;
+uschar * s;
+BOOL initial = TRUE;
+int rc, yield = FAIL;
+
+HDEBUG(D_auth)
+  debug_printf("GNU SASL: initialising session for %s, mechanism %s\n",
+      ablock->name, ob->server_mech);
+
+*buffer = 0;
+
+#ifndef DISABLE_TLS
+if (tls_out.channelbinding && ob->client_channelbinding)
+  {
+# ifdef EXPERIMENTAL_TLS_RESUME
+  if (!tls_out.ext_master_secret && tls_out.resumption == RESUME_USED)
+    {		/* per RFC 7677 section 4 */
+    string_format(buffer, buffsize, "%s",
+      "channel binding not usable on resumed TLS without extended-master-secret");
+    return FAIL;
+    }
+# endif
+# ifdef CHANNELBIND_HACK
+  /* This is a gross hack to get around the library a) requiring that
+  c-b was already set, at the _start() call, and b) caching a b64'd
+  version of the binding then which it never updates. */
+
+  gsasl_callback_hook_set(gsasl_ctx, tls_out.channelbinding);
+# endif
+  }
+#endif
+
+if ((rc = gsasl_client_start(gsasl_ctx, CCS ob->server_mech, &sctx)) != GSASL_OK)
+  {
+  string_format(buffer, buffsize, "GNU SASL: session start failure: %s (%s)",
+      gsasl_strerror_name(rc), gsasl_strerror(rc));
+  HDEBUG(D_auth) debug_printf("%s\n", buffer);
+  return ERROR;
+  }
+
+cb_state.ablock = ablock;
+cb_state.currently = CURRENTLY_CLIENT;
+gsasl_session_hook_set(sctx, &cb_state);
+
+/* Set properties */
+
+if (  !set_client_prop(sctx, GSASL_SCRAM_SALTED_PASSWORD, ob->client_spassword,
+		  0, buffer, buffsize)
+      &&
+      !set_client_prop(sctx, GSASL_PASSWORD, ob->client_password,
+		  0, buffer, buffsize)
+   || !set_client_prop(sctx, GSASL_AUTHID, ob->client_username,
+		  0, buffer, buffsize)
+   || !set_client_prop(sctx, GSASL_AUTHZID, ob->client_authz,
+		  PROP_OPTIONAL, buffer, buffsize)
+   )
+  return ERROR;
+
+#ifndef DISABLE_TLS
+if (tls_out.channelbinding)
+  if (ob->client_channelbinding)
+    {
+    HDEBUG(D_auth) debug_printf("Auth %s: Enabling channel-binding\n",
+	ablock->name);
+# ifndef CHANNELBIND_HACK
+    gsasl_property_set(sctx, GSASL_CB_TLS_UNIQUE, CCS tls_out.channelbinding);
+# endif
+    }
+  else
+    HDEBUG(D_auth)
+      debug_printf("Auth %s: Not enabling channel-binding (data available)\n",
+	  ablock->name);
+#endif
+
+/* Run the SASL conversation with the server */
+
+for(s = NULL; ;)
+  {
+  uschar * outstr;
+  BOOL fail;
+
+  rc = gsasl_step64(sctx, CS s, CSS &outstr);
+
+  fail = initial
+    ? smtp_write_command(sx, SCMD_FLUSH,
+			outstr ? "AUTH %s %s\r\n" : "AUTH %s\r\n",
+			ablock->public_name, outstr) <= 0
+    : outstr
+    ? smtp_write_command(sx, SCMD_FLUSH, "%s\r\n", outstr) <= 0
+    : FALSE;
+  if (outstr && *outstr) free(outstr);
+  if (fail)
+    {
+    yield = FAIL_SEND;
+    goto done;
+    }
+  initial = FALSE;
+
+  if (rc != GSASL_NEEDS_MORE)
+    {
+    if (rc != GSASL_OK)
+      {
+      string_format(buffer, buffsize, "gsasl: %s", gsasl_strerror(rc));
+      break;
+      }
+
+    /* expecting a final 2xx from the server, accepting the AUTH */
+
+    if (smtp_read_response(sx, buffer, buffsize, '2', timeout))
+      yield = OK;
+    break;	/* from SASL sequence loop */
+    }
+
+  /* 2xx or 3xx response is acceptable.  If 2xx, no further input */
+
+  if (!smtp_read_response(sx, buffer, buffsize, '3', timeout))
+    if (errno == 0 && buffer[0] == '2')
+      buffer[4] = '\0';
+    else
+      {
+      yield = FAIL;
+      goto done;
+      }
+  s = buffer + 4;
+  }
+
+done:
+HDEBUG(D_auth)
+  {
+  const uschar * s = CUS gsasl_property_fast(sctx, GSASL_SCRAM_SALTED_PASSWORD);
+  if (s) debug_printf(" - SaltedPassword: '%s'\n", s);
+  }
+
+gsasl_finish(sctx);
+return yield;
+}
+
+static int
+client_callback(Gsasl *ctx, Gsasl_session *sctx, Gsasl_property prop, auth_instance *ablock)
+{
+HDEBUG(D_auth) debug_printf("GNU SASL callback %s for %s/%s as client\n",
+	    gsasl_prop_code_to_name(prop), ablock->name, ablock->public_name);
+switch (prop)
+  {
+  case GSASL_CB_TLS_UNIQUE:
+    HDEBUG(D_auth)
+      debug_printf(" filling in\n");
+    gsasl_property_set(sctx, GSASL_CB_TLS_UNIQUE, CCS tls_out.channelbinding);
+    break;
+  default:
+    HDEBUG(D_auth)
+      debug_printf(" not providing one\n");
+    break;
+  }
+return GSASL_NO_CALLBACK;
+}
+
+/*************************************************
+*                Diagnostic API                  *
+*************************************************/
+
+void
+auth_gsasl_version_report(FILE *f)
+{
+const char *runtime;
+runtime = gsasl_check_version(NULL);
+fprintf(f, "Library version: GNU SASL: Compile: %s\n"
+	   "                           Runtime: %s\n",
+	GSASL_VERSION, runtime);
+}
+
+
+
+/* Dummy */
+void auth_gsasl_macros(void) {}
+
+#endif   /*!MACRO_PREDEF*/
+#endif  /* AUTH_GSASL */
+
+/* End of gsasl_exim.c */