Search code examples
phpmacosposix

Temporarily change identity of running process

I want to temporarily change the identity of a running root process.

I have read the way to do this is to first call setegid and then seteuid.

The problem is that the group somehow is ignored:

<?php
# This is executed as root.
var_dump(posix_setegid(61));   # localaccounts(61)
var_dump(posix_seteuid(502));  # bot(502)

$fp = fopen("/tmp/test", "w+b");

system("ls -la /tmp/test");

unlink("/tmp/test");

Outputs:

$ sudo php -f /tmp/test.php
bool(true)
bool(true)
-rw-r--r--  1 bot  wheel  0 Feb  2 17:49 /tmp/test

But I expect it to output:

-rw-r--r--  1 bot  localaccounts  0 Feb  2 17:49 /tmp/test

Am I missing something?

UPDATE: It works on a linux machine. Is this some weird OSX quirk?

Solution

  • Mac os x derives from the BSD branch of Unix, and

    According to BSD Unix semantics, the group ownership given to a newly created file is unconditionally inherited from the group ownership of the directory in which it is created.

    (From https://en.m.wikipedia.org/wiki/User_identifier#Effective_user_ID - I can't find a better source)

    You can always use chgrp to change the group after the file is created