fix potential unwarranted memberships in nested groups from LDAP

- the issue was present only when using PHP based resolving of nested
  group members. Normally nested members are common in AD (and Samba4) and
  are resolved per LDAP_MATCHING_RULE_IN_CHAIN by default
- resolving nested members is recursive
- when the cache entry was created it happend for intermediate groups, too,
  containing members from the parent group
- the check was added to only cache the root group with its members
- a runtime cache stores intermediate ldap read results


Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

apps/user_ldap/lib/Group_LDAP.php

@@ -248,7 +248,12 @@ private function _groupMembers(string $dnGroup, ?array &$seen = null): array {
 			// but not included in the results laters on
 			$excludeFromResult = $dnGroup;
 		}
+		// cache only base groups, otherwise groups get additional unwarranted members
+		$shouldCacheResult = count($seen) === 0;
+
+		static $rawMemberReads = []; // runtime cache for intermediate ldap read results
 		$allMembers = [];
+
 		if (array_key_exists($dnGroup, $seen)) {
 			return [];
 		}
@@ -290,7 +295,11 @@ private function _groupMembers(string $dnGroup, ?array &$seen = null): array {
 		}
 
 		$seen[$dnGroup] = 1;
-		$members = $this->access->readAttribute($dnGroup, $this->access->connection->ldapGroupMemberAssocAttr);
+		$members = $rawMemberReads[$dnGroup] ?? null;
+		if ($members === null) {
+			$members = $this->access->readAttribute($dnGroup, $this->access->connection->ldapGroupMemberAssocAttr);
+			$rawMemberReads[$dnGroup] = $members;
+		}
 		if (is_array($members)) {
 			$fetcher = function ($memberDN) use (&$seen) {
 				return $this->_groupMembers($memberDN, $seen);
@@ -306,7 +315,10 @@ private function _groupMembers(string $dnGroup, ?array &$seen = null): array {
 			}
 		}
 
-		$this->access->connection->writeToCache($cacheKey, $allMembers);
+		if ($shouldCacheResult) {
+			$this->access->connection->writeToCache($cacheKey, $allMembers);
+			unset($rawMemberReads[$dnGroup]);
+		}
 		if (isset($attemptedLdapMatchingRuleInChain)
 			&& $this->access->connection->ldapMatchingRuleInChainState === Configuration::LDAP_SERVER_FEATURE_UNKNOWN
 			&& !empty($allMembers)