Add a 'exclusive client' option to the config file

src/cryfs/config/CryConfig.cpp

@@ -21,11 +21,11 @@ using cpputils::Random;
 namespace cryfs {
 
 CryConfig::CryConfig()
-: _rootBlob(""), _encKey(""), _cipher(""), _version(""), _createdWithVersion(""), _blocksizeBytes(0), _filesystemId(FilesystemID::Null()), _hasVersionNumbers(true) {
+: _rootBlob(""), _encKey(""), _cipher(""), _version(""), _createdWithVersion(""), _blocksizeBytes(0), _filesystemId(FilesystemID::Null()), _exclusiveClientId(none), _hasVersionNumbers(true) {
 }
 
 CryConfig::CryConfig(CryConfig &&rhs)
-: _rootBlob(std::move(rhs._rootBlob)), _encKey(std::move(rhs._encKey)), _cipher(std::move(rhs._cipher)), _version(std::move(rhs._version)), _createdWithVersion(std::move(rhs._createdWithVersion)), _blocksizeBytes(rhs._blocksizeBytes), _filesystemId(std::move(rhs._filesystemId)), _hasVersionNumbers(rhs._hasVersionNumbers) {
+: _rootBlob(std::move(rhs._rootBlob)), _encKey(std::move(rhs._encKey)), _cipher(std::move(rhs._cipher)), _version(std::move(rhs._version)), _createdWithVersion(std::move(rhs._createdWithVersion)), _blocksizeBytes(rhs._blocksizeBytes), _filesystemId(std::move(rhs._filesystemId)), _exclusiveClientId(std::move(rhs._exclusiveClientId)), _hasVersionNumbers(rhs._hasVersionNumbers) {
 }
 
 CryConfig CryConfig::load(const Data &data) {
@@ -41,6 +41,7 @@ CryConfig CryConfig::load(const Data &data) {
   cfg._version = pt.get<string>("cryfs.version", "0.8"); // CryFS 0.8 didn't specify this field, so if the field doesn't exist, it's 0.8.
   cfg._createdWithVersion = pt.get<string>("cryfs.createdWithVersion", cfg._version); // In CryFS <= 0.9.2, we didn't have this field, but also didn't update cryfs.version, so we can use this field instead.
   cfg._blocksizeBytes = pt.get<uint64_t>("cryfs.blocksizeBytes", 32832); // CryFS <= 0.9.2 used a 32KB block size which was this physical block size.
+  cfg._exclusiveClientId = pt.get_optional<uint32_t>("cryfs.exclusiveClientId");
 #ifndef CRYFS_NO_COMPATIBILITY
   cfg._hasVersionNumbers = pt.get<bool>("cryfs.migrations.hasVersionNumbers", false);
 #endif
@@ -65,6 +66,9 @@ Data CryConfig::save() const {
   pt.put<string>("cryfs.createdWithVersion", _createdWithVersion);
   pt.put<uint64_t>("cryfs.blocksizeBytes", _blocksizeBytes);
   pt.put<string>("cryfs.filesystemId", _filesystemId.ToString());
+  if (_exclusiveClientId != none) {
+    pt.put("cryfs.exclusiveClientId", *_exclusiveClientId);
+  }
 #ifndef CRYFS_NO_COMPATIBILITY
   pt.put("cryfs.migrations.hasVersionNumbers", _hasVersionNumbers);
 #endif
@@ -130,6 +134,14 @@ void CryConfig::SetFilesystemId(const FilesystemID &value) {
   _filesystemId = value;
 }
 
+optional<uint32_t> CryConfig::ExclusiveClientId() const {
+  return _exclusiveClientId;
+}
+
+void CryConfig::SetExclusiveClientId(optional<uint32_t> value) {
+  _exclusiveClientId = value;
+}
+
 #ifndef CRYFS_NO_COMPATIBILITY
 bool CryConfig::HasVersionNumbers() const {
   return _hasVersionNumbers;

src/cryfs/config/CryConfig.h

@@ -38,6 +38,11 @@ public:
   const FilesystemID &FilesystemId() const;
   void SetFilesystemId(const FilesystemID &value);
 
+  // If the exclusive client Id is set, then additional integrity measures (i.e. treating missing blocks as integrity violations) are enabled.
+  // Because this only works in a single-client setting, only this one client Id is allowed to access the file system.
+  boost::optional<uint32_t> ExclusiveClientId() const;
+  void SetExclusiveClientId(boost::optional<uint32_t> value);
+
 #ifndef CRYFS_NO_COMPATIBILITY
   // This is a trigger to recognize old file systems that didn't have version numbers.
   // Version numbers cannot be disabled, but the file system will be migrated to version numbers automatically.
@@ -56,6 +61,7 @@ private:
   std::string _createdWithVersion;
   uint64_t _blocksizeBytes;
   FilesystemID _filesystemId;
+  boost::optional<uint32_t> _exclusiveClientId;
 #ifndef CRYFS_NO_COMPATIBILITY
   bool _hasVersionNumbers;
 #endif

test/cryfs/config/CryConfigTest.cpp

@@ -5,6 +5,7 @@
 using namespace cryfs;
 using cpputils::Data;
 using cpputils::DataFixture;
+using boost::none;
 
 class CryConfigTest: public ::testing::Test {
 public:
@@ -165,3 +166,43 @@ TEST_F(CryConfigTest, FilesystemID_AfterSaveAndLoad) {
     CryConfig loaded = SaveAndLoad(std::move(cfg));
     EXPECT_EQ(fixture, loaded.FilesystemId());
 }
+
+TEST_F(CryConfigTest, ExclusiveClientId_Init) {
+    EXPECT_EQ(none, cfg.ExclusiveClientId());
+}
+
+TEST_F(CryConfigTest, ExclusiveClientId_Some) {
+    cfg.SetExclusiveClientId(0x12345678u);
+    EXPECT_EQ(0x12345678u, cfg.ExclusiveClientId().value());
+}
+
+TEST_F(CryConfigTest, ExclusiveClientId_None) {
+    cfg.SetExclusiveClientId(0x12345678u);
+    cfg.SetExclusiveClientId(none);
+    EXPECT_EQ(none, cfg.ExclusiveClientId());
+}
+
+TEST_F(CryConfigTest, ExclusiveClientId_Some_AfterMove) {
+    cfg.SetExclusiveClientId(0x12345678u);
+    CryConfig moved = std::move(cfg);
+    EXPECT_EQ(0x12345678u, moved.ExclusiveClientId().value());
+}
+
+TEST_F(CryConfigTest, ExclusiveClientId_None_AfterMove) {
+    cfg.SetExclusiveClientId(0x12345678u);
+    cfg.SetExclusiveClientId(none);
+    CryConfig moved = std::move(cfg);
+    EXPECT_EQ(none, moved.ExclusiveClientId());
+}
+
+TEST_F(CryConfigTest, ExclusiveClientId_Some_AfterSaveAndLoad) {
+    cfg.SetExclusiveClientId(0x12345678u);
+    CryConfig loaded = SaveAndLoad(std::move(cfg));
+    EXPECT_EQ(0x12345678u, loaded.ExclusiveClientId().value());
+}
+
+TEST_F(CryConfigTest, ExclusiveClientId_None_AfterSaveAndLoad) {
+    cfg.SetExclusiveClientId(none);
+    CryConfig loaded = SaveAndLoad(std::move(cfg));
+    EXPECT_EQ(none, loaded.ExclusiveClientId());
+}