Log diagnostic messages if errors occur during LDAP auth.

Diagnostic messages seem likely to help users diagnose root
causes more easily, so let's report them as errdetail.

Author: Thomas Munro
Reviewed-By: Ashutosh Bapat, Christoph Berg, Alvaro Herrera, Peter Eisentraut
Discussion: https://postgr.es/m/CAEepm=2_dA-SYpFdmNVwvKsEBXOUj=K4ooKovHmvj6jnMdt8dw@mail.gmail.com

src/backend/libpq/auth.c

@@ -2305,6 +2305,8 @@ CheckBSDAuth(Port *port, char *user)
  */
 #ifdef USE_LDAP
 
+static int errdetail_for_ldap(LDAP *ldap);
+
 /*
  * Initialize a connection to the LDAP server, including setting up
  * TLS if requested.
@@ -2332,7 +2334,9 @@ InitializeLDAPConnection(Port *port, LDAP **ldap)
 	if ((r = ldap_set_option(*ldap, LDAP_OPT_PROTOCOL_VERSION, &ldapversion)) != LDAP_SUCCESS)
 	{
 		ereport(LOG,
-				(errmsg("could not set LDAP protocol version: %s", ldap_err2string(r))));
+				(errmsg("could not set LDAP protocol version: %s",
+						ldap_err2string(r)),
+				 errdetail_for_ldap(*ldap)));
 		ldap_unbind(*ldap);
 		return STATUS_ERROR;
 	}
@@ -2385,7 +2389,9 @@ InitializeLDAPConnection(Port *port, LDAP **ldap)
 #endif
 		{
 			ereport(LOG,
-					(errmsg("could not start LDAP TLS session: %s", ldap_err2string(r))));
+					(errmsg("could not start LDAP TLS session: %s",
+							ldap_err2string(r)),
+					 errdetail_for_ldap(*ldap)));
 			ldap_unbind(*ldap);
 			return STATUS_ERROR;
 		}
@@ -2508,7 +2514,9 @@ CheckLDAPAuth(Port *port)
 		{
 			ereport(LOG,
 					(errmsg("could not perform initial LDAP bind for ldapbinddn \"%s\" on server \"%s\": %s",
-							port->hba->ldapbinddn, port->hba->ldapserver, ldap_err2string(r))));
+							port->hba->ldapbinddn, port->hba->ldapserver,
+							ldap_err2string(r)),
+					 errdetail_for_ldap(ldap)));
 			ldap_unbind(ldap);
 			pfree(passwd);
 			return STATUS_ERROR;
@@ -2534,7 +2542,8 @@ CheckLDAPAuth(Port *port)
 		{
 			ereport(LOG,
 					(errmsg("could not search LDAP for filter \"%s\" on server \"%s\": %s",
-							filter, port->hba->ldapserver, ldap_err2string(r))));
+							filter, port->hba->ldapserver, ldap_err2string(r)),
+					 errdetail_for_ldap(ldap)));
 			ldap_unbind(ldap);
 			pfree(passwd);
 			pfree(filter);
@@ -2573,7 +2582,9 @@ CheckLDAPAuth(Port *port)
 			(void) ldap_get_option(ldap, LDAP_OPT_ERROR_NUMBER, &error);
 			ereport(LOG,
 					(errmsg("could not get dn for the first entry matching \"%s\" on server \"%s\": %s",
-							filter, port->hba->ldapserver, ldap_err2string(error))));
+							filter, port->hba->ldapserver,
+							ldap_err2string(error)),
+					 errdetail_for_ldap(ldap)));
 			ldap_unbind(ldap);
 			pfree(passwd);
 			pfree(filter);
@@ -2618,23 +2629,46 @@ CheckLDAPAuth(Port *port)
 							port->hba->ldapsuffix ? port->hba->ldapsuffix : "");
 
 	r = ldap_simple_bind_s(ldap, fulluser, passwd);
-	ldap_unbind(ldap);
 
 	if (r != LDAP_SUCCESS)
 	{
 		ereport(LOG,
 				(errmsg("LDAP login failed for user \"%s\" on server \"%s\": %s",
-						fulluser, port->hba->ldapserver, ldap_err2string(r))));
+						fulluser, port->hba->ldapserver, ldap_err2string(r)),
+				 errdetail_for_ldap(ldap)));
+		ldap_unbind(ldap);
 		pfree(passwd);
 		pfree(fulluser);
 		return STATUS_ERROR;
 	}
 
+	ldap_unbind(ldap);
 	pfree(passwd);
 	pfree(fulluser);
 
 	return STATUS_OK;
 }
+
+/*
+ * Add a detail error message text to the current error if one can be
+ * constructed from the LDAP 'diagnostic message'.
+ */
+static int
+errdetail_for_ldap(LDAP *ldap)
+{
+	char	   *message;
+	int			rc;
+
+	rc = ldap_get_option(ldap, LDAP_OPT_DIAGNOSTIC_MESSAGE, &message);
+	if (rc == LDAP_SUCCESS && message != NULL)
+	{
+		errdetail("LDAP diagnostics: %s", message);
+		ldap_memfree(message);
+	}
+
+	return 0;
+}
+
 #endif							/* USE_LDAP */
 
 

src/test/ldap/t/001_auth.pl

@@ -2,7 +2,7 @@ use strict;
 use warnings;
 use TestLib;
 use PostgresNode;
-use Test::More tests => 14;
+use Test::More tests => 15;
 
 my ($slapd, $ldap_bin_dir, $ldap_schema_dir);
 
@@ -175,3 +175,12 @@ $node->reload;
 
 $ENV{"PGPASSWORD"} = 'secret1';
 test_access($node, 'test1', 0, 'combined LDAP URL and search filter');
+
+note "diagnostic message";
+
+unlink($node->data_dir . '/pg_hba.conf');
+$node->append_conf('pg_hba.conf', qq{local all all ldap ldapserver=$ldap_server ldapport=$ldap_port ldapprefix="uid=" ldapsuffix=",dc=example,dc=net" ldaptls=1});
+$node->reload;
+
+$ENV{"PGPASSWORD"} = 'secret1';
+test_access($node, 'test1', 2, 'any attempt fails due to unsupported TLS');