mount: Fix updating user groups in master after its restart

The bug originated from clearing mount's group cache on master disconnected
event and using the same cache to register user's groups in the master later on.
The cache was already empty when attempting the registration so there were no
groups to tell master about so the operation performed on the mounted filesystem
failed.

This fix changes the registration part in the client so that it uses client
context to populate the cache and update credentials (groups) in master if
the group cache is empty, for example due to disconnection from master.

Context references were made non-const because updating groups in group cache
requires assigning a new gid value in the client context.

Fixes bug introduced by 7e7ad72

Change-Id: Idac2ebc74e73ca306462e07bd3b943c2efa73a0d

src/common/user_groups.h

@@ -0,0 +1,41 @@
+/*
+   Copyright 2013-2020 Lizard sp. z o.o.
+
+   This file is part of LizardFS.
+
+   LizardFS is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, version 3.
+
+   LizardFS is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with LizardFS. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "common/platform.h"
+
+#include <cstdint>
+
+namespace user_groups {
+
+constexpr std::uint32_t kSecondaryGroupsBit = (std::uint32_t)1 << 31;
+
+constexpr bool isGroupCacheId(std::uint32_t groupsId) noexcept {
+  return static_cast<bool>(groupsId & kSecondaryGroupsBit);
+}
+
+constexpr std::uint32_t encodeGroupCacheId(std::uint32_t groupsId) noexcept {
+  return groupsId | kSecondaryGroupsBit;
+}
+
+constexpr std::uint32_t decodeGroupCacheId(std::uint32_t groupsId) noexcept {
+  return groupsId & ~kSecondaryGroupsBit;
+}
+
+} // namespace user_groups

src/master/matoclserv.cc

@@ -60,6 +60,7 @@
 #include "common/serialized_goal.h"
 #include "common/slogger.h"
 #include "common/sockets.h"
+#include "common/user_groups.h"
 #include "master/changelog.h"
 #include "master/chartsdata.h"
 #include "master/chunks.h"
@@ -948,14 +949,12 @@ static inline void matoclserv_ugid_remap(matoclserventry *eptr,uint32_t *auid,ui
 }
 
 static inline uint8_t matoclserv_check_group_cache(matoclserventry *eptr, uint32_t gid) {
-	static constexpr uint32_t kSecondaryGroupsBit = (uint32_t)1 << 31;
-
-	if ((gid & kSecondaryGroupsBit) == 0) {
+	if (!user_groups::isGroupCacheId(gid)) {
 		return LIZARDFS_STATUS_OK;
 	}
 
 	assert(eptr && eptr->sesdata);
-	auto it = eptr->sesdata->group_cache.find(gid ^ kSecondaryGroupsBit);
+	auto it = eptr->sesdata->group_cache.find(user_groups::decodeGroupCacheId(gid));
 	return it == eptr->sesdata->group_cache.end() ? LIZARDFS_ERROR_GROUPNOTREGISTERED : LIZARDFS_STATUS_OK;
 }
 
@@ -971,12 +970,10 @@ static inline FsContext matoclserv_get_context(matoclserventry *eptr) {
  * Returns FsContext with session data and uid/gid data
  */
 static inline FsContext matoclserv_get_context(matoclserventry *eptr, uint32_t uid, uint32_t gid) {
-	static constexpr uint32_t kSecondaryGroupsBit = (uint32_t)1 << 31;
-
 	assert(eptr && eptr->sesdata);
 
-	if (gid & kSecondaryGroupsBit) {
-		auto it = eptr->sesdata->group_cache.find(gid ^ kSecondaryGroupsBit);
+	if (user_groups::isGroupCacheId(gid)) {
+		auto it = eptr->sesdata->group_cache.find(user_groups::decodeGroupCacheId(gid));
 		if (it == eptr->sesdata->group_cache.end()) {
 			throw std::runtime_error("Missing group data in session cache");
 		}