Focus on Linux
How to check UID of process on the other side of local TCP/UDP connection Nov 24 2006 06:11PM
rainmailbox2001-ola yahoo ca

I have the following situation:
- Client communicates with server via TCP or UDP.
- Both client and server are on the same local host.
- Server runs with root privilege.

Now, client connects to server. Server has to check uid of the client. How it can be done?
I need a solution that can be ported to all modern Unix and Linux systems.

The most simple solution I came with is as follows:
1. Client connects to server.
2. Server asks client to create file with random name, for example /tmp/check.6723
3. Client generates the file.
4. Server checks the owner of the file.

The owner of the file is the UID under which client is running.

the problem is that it requires some additional communication between
server and client. My programs can communicate hundreds times a second
so creating, checking and removing the file is a big performance issue.

Do you have any ideas how this local authentication can be achieved in some different way?

was also thinking about using Unix sockets for communication, but it
seems that they also lack any mechanism for authenticating the client.
Anyways, I would prefer to stick with TCP/UDP, because this is what my
programs use already, and I don't really want to change everything to
Unix sockets (unless of course Unix sockets are the only good way to
resolve my problems).


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