Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com Date: Tue, 4 Jun 2002 10:51:38 -0400 (EDT) From: David E Euresti To: egor duda Subject: Re: Duplicating Unix Domain Sockets In-Reply-To: <291438343308.20020604101630@logos-m.ru> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII On Tue, 4 Jun 2002, egor duda wrote: > Hi! > > It's not enough to just pass numerical value of descriptor between > processes. Each cygwin fd has several win32 handles associated with > it, which are used to actually do the job, to read or write the data, > to perform synchronization, etc. If you want to pass fd1 from proc1 to > proc2, you have to duplicate all win32 handles associated with fd1 > into address space of proc2. This can be done by DuplicateHandle () > function, but if you take a look on its docs on msdn, you'll see that > it requires process handles of proc1 and proc2 to work. Given that > proc1 and proc2 can be absolutely unrelated and run from different > accounts, there's no secure way to obtain those process handles > without help from some mediator process which run at high enough level > of privileges. Oh I know it's not enough just passing a number. I've already got a user land application passing file descriptor by passing struct passfd { unsigned int uiMagic; // Magic number to see if it's right DWORD dwProcessID; // Process ID of sender HANDLE hHandle; // Handle in sender's process BOOL bBinary; // is it Binary or Text? BOOL bRead; // Is it read? BOOL bWrite; // Is it write DWORD dwDevice; // Device type as listed in windows_device_names in path.cc }; So basically I pass this info in at the beginning of a packet. And then the receiving end calls DuplicateHandle, followed by cygwin_handle_to_fd. It works well except it doesn't mark the right socket types. i.e. UDP, TCP, AF_UNIX etc. (I've sent the code before search for my name in the archive and you'll find it titled "File Descriptor passing fun". Another problem with this is that there's a bit of synchronization needed because the sending process can't close the socket until it's been duplicated. This will actually happen in the suggestion I had. > That's what cygwin daemon is for -- to provide a > services that require high privileges to normal non-privileged > processes. After such handle duplication service (with appropriate > security checks) is implemented in cygwin daemon, it would be simple > to augment AF_UNIX sockets protocol to be able to pass auxiliary > information such as fds. > Well as I have to have this to graduate, I could work on this. But somebody needs to tell me where to start looking. Because i've looked through the source and I don't really get it. Thanks, David -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Bug reporting: http://cygwin.com/bugs.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/