Bug#766053: systemd-cron cannot edit user crontabs

[Alexandre Detiste]

control: tags -1 fixed-upstream

Hi,

I'm still working on this last major bug of systemd-cron.

I came up with this setuid helper, that is called by crontab when needed:
https://github.com/systemd-cron/systemd-cron/blob/setuid/src/bin/crontab_setuid.c

I avoided the most obvious pitfalls: string format attacks,
tmp files/symlinks attacks (it uses stdin/stdout to pass crontab data);
and I made it as bare as possible.

Please review it

Alexandre

--

systemd-cron postinst script needs to do this too:
	chown root:root /var/spool/cron/crontabs
	chmod 770 /var/spool/cron/crontabs