I'm trying to do the safe thing, and have a program that needs to runs as root to drop its privileges when it doesn't need them. This works well if I chmod my binary with the SUID bit, and make it belong to root, as now I have UID = some user, and EUID = root, so I can use seteuid(0) and seteuid(getuid()) to respectively raise and drop admin rights.
But if I use sudo instead of setting the SUID, then UID == EUID == 0, and so calling seteuid(getuid()) won't have any effect. And I can't just change UID to some value from some random user, as the setuid() man page clearly states that if it is called from a program running as root, one loses the privileges for good, with no hope of getting them back.
So, how do I make my program lose temporarily its privileges when run using sudo?
seteuid(some random uid) to drop privileges, seteuid(0) to get them back, when running as root.