release() not sufficently synchronized

[infeo]

We use path/data locks in order to synchronize callbacks, based on An Efficient Locking Scheme for Path-based File
Systems.

The release() callback is not covered by this paper. Nonetheless, it requires synchronization, as implemented in ReadOnlyAdapter:

fuse-nio-adapter/src/main/java/org/cryptomator/frontend/fuse/ReadOnlyAdapter.java

Lines 358 to 360 in 3d70693

	public int release(String path, FileInfo fi) {
	try (PathLock pathLock = lockManager.lockForReading(path);
	DataLock _ = pathLock.lockDataForReading()) {

The problem with only acquiring read locks is, that while reading data, the resource can be simultaneously released, which might lead to an inconsistent state. Especially in combination with cryptofs, which requires an external locking mechanism, this can pollute the filesystem state.

[infeo]

My suggestions is to acquire an Write lock on the data when releasing a resource.