Dropping Root Permissions In Python

I'd like to have a Python program start listening on port 80, but after that execute without root permissions. Is there a way to drop root or to get port 80 without it?

You won't be able to open a server on port 80 without root privileges, this is a restriction on the OS level. So the only solution is to drop root privileges after you have opened the port.

Here is a possible solution to drop root privileges in Python: Dropping privileges in Python. This is a good solution in general, but you'll also have to add os.setgroups([]) to the function to ensure that the group membership of the root user is not retained.

I copied and cleaned up the code a little bit, and removed logging and the exception handlers so it is left up to you to handle OSError properly (it will be thrown when the process is not allowed to switch its effective UID or GID):

import os, pwd, grp

def drop_privileges(uid_name='nobody', gid_name='nogroup'):
    if os.getuid() != 0:
        # We're not root so, like, whatever dude
        return

    # Get the uid/gid from the name
    running_uid = pwd.getpwnam(uid_name).pw_uid
    running_gid = grp.getgrnam(gid_name).gr_gid

    # Remove group privileges
    os.setgroups([])

    # Try setting the new uid/gid
    os.setgid(running_gid)
    os.setuid(running_uid)

    # Ensure a very conservative umask
    old_umask = os.umask(077)

I recommend using authbind to start your Python program, so none of it has to run as root.

https://en.wikipedia.org/wiki/Authbind

It is not a good idea to ask the user to enter his/her user-name and group whenever I need to drop privileges. Here is a slightly modified version of Tamás's code which will drop privileges and switch to the user who initiated the sudo command. I am assuming you are using sudo (if not, use Tamás's code).

#!/usr/bin/env python3

import os, pwd, grp

#Throws OSError exception (it will be thrown when the process is not allowed
#to switch its effective UID or GID):
def drop_privileges():
    if os.getuid() != 0:
        # We're not root so, like, whatever dude
        return

    # Get the uid/gid from the name
    user_name = os.getenv("SUDO_USER")
    pwnam = pwd.getpwnam(user_name)

    # Remove group privileges
    os.setgroups([])

    # Try setting the new uid/gid
    os.setgid(pwnam.pw_gid)
    os.setuid(pwnam.pw_uid)

    #Ensure a reasonable umask
    old_umask = os.umask(0o22)


#Test by running...
#./drop_privileges
#sudo ./drop_privileges
if __name__ == '__main__':
    print(os.getresuid())
    drop_privileges()
    print(os.getresuid())

systemd can do it for you, if you start your program through systemd, systemd can hand off the already-open listening socket to it, and it can also activate your program on first connection. and you don't even need to daemonize it.
If you are going to go with the standalone approach, you need the capability CAP_NET_BIND_SERVICE (check capabilities man page). This can be done on a program-by-program basis with the correct command line tool, or by making your application (1) be suid root (2) start up (3) listen to the port (4) drop privileges / capabilities immediately.

Remember that suid root programs come with lots of security considerations (clean and secure environment, umask, privileges, rlimits, all those things are things that your program is going to have to set up correctly). If you can use something like systemd, all the better then.

Dropping Root Permissions In Python

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