Question

(This question has identical title, but question body asks it in scripting point of view, e.g. su -c, don’t dupe this to that)

I have a Qt GUI app that needs to perform some file operations in /etc based on user input. One option would probably to use system() with sudo, but even that requires messing with sudoers file in some point. I also would like not to do system() plus script hacks to modify the files, but proper file operations.

What is the best way to programmatically elevate my applications rights to do this?

Edit: as a bonus, it’d be nice if it would work on Maemo/Meego/other handhelds too (afaik PolicyKit isn’t available there..)

Answer 1

I would write a separate program altogether. Something along the lines of this philosophy. Basically – write a simple program that does exactly what you need, and control its behaviour with file permissions on the filesystem. Mainly,

Do as little as possible in setuid programs.

A setuid program must operate in a
very dangerous environment: a user is
under complete control of its fds,
args, environ, cwd, tty, rlimits,
timers, signals, and more. Even worse,
the list of controlled items varies
from one vendor’s UNIX to the next, so
it is very difficult to write portable
code that cleans up everything.

Of the twenty most recent sendmail
security holes, eleven worked only
because the entire sendmail system is
setuid.

Only one qmail program is setuid:
qmail-queue. Its only purpose is to
add a new mail message to the outgoing
queue.

And,

Do as little as possible as root.

The entire sendmail system runs as
root, so there’s no way that its
mistakes can be caught by the
operating system’s built-in
protections. In contrast, only two
qmail programs, qmail-start and
qmail-lspawn, run as root.