No. There would be no need for this API if file handles were shared as you describe in Win32. The API has the kernel create in one process a new file handle that points to the same kernel data structure as an existing file handle of another process. This is the same thing that happens in Unix when you pass an open file descriptor over a socket. It is just that the interface for getting it done is different.

File handles in Windows are actually very similar to file handles in Unix in many ways (including that they can't be used by another process but can be used by other threads of the same process). For example, the seek position is shared between the two file handles/descriptors in the two processes after this type of operation in both Windows and Unix.

One difference between the two scenarios regarding protections is that the Windows API requires that one process be able to get a handle to another process (or to the other two processes) with sufficient access to be allowed to copy or create the other process's handle. With the Unix API, the processes need to cooperate (of course) but neither process needs any special access permissions to the other.

Interestingly, giving out access to your process such that DuplicateHandle() can be used on that process actually means that one can also fairly easily get unrestricted access to the process. So security concerns could easily make the use of this API unacceptable in some scenarios.

In contrast, one of the example scenarios for the use of the Unix API is to allow processes to share privileges while keeping more control.

For example, you could have a server process that has special access to manage the directory where log files are kept. A client could be given a file handle that only allows them to append to a log file, a log file that they have no permissions to access in a directory that they have no permissions to access. Yet they can write directly to the log file, not having to pass data through some server process to have it append it for them. (But if the server process is compromised, it only has access to log files, it can't read/write pages of memory of every potential client process.)

- tye        

In reply to Re^2: Pass filehandles around between (unrelated) processes on Windows (protections) by tye
in thread Pass filehandles around between (unrelated) processes on Windows by Corion

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