instchown: operate on fds, not filenames.

[schmonz]

The previous code had been flagged by CodeQL as "TOCTOU". It's not -- at worst, it's time-of-chown to time-of-chmod -- but this will run more efficiently (and make the warnings go away).

Tested like so:

#!/bin/sh

set -e

for i in true mandoc; do
	sudo rm -rf /var/tmp/qmail-staging $(head -1 conf-qmail)
	make clean
	make -j 4 it man NROFF=$i test
	env DESTDIR=/var/tmp/qmail-staging make package
	sudo env DESTDIR=/var/tmp/qmail-staging ./instchown
	sudo make package
	sudo ./instchown
	sudo ./instcheck
done

[josuah]

Who knows, some deployments of notqmail might be done automatically, and better not have some different file used between the chown and chmod. I do not see a TOCTOU though, maybe I missed it...

Does not hurt to have it done with a file descriptor...

[schmonz]

Yes, AFAICT it's limited to time-of-chown vs time-of-chmod. But (if I can get it to actually work) as you say, seems wise to not be in position to find out whether it's anything worse.

[DerDakon]

While I think the automated report it rather pointless and this is no real issue, I actually like that change because it is way more efficient for the OS at the end.

[DerDakon]

wrong checkbox