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Issue privileges as a regular non-root user for a sandbox?

Can I use a set of C libraries or system calls to reset all user privileges on POSIX, or at least Linux? Please note that I am not asking how to refuse privileges root, and that, apparently, all other StackOverflow search results are asking and responding.

I need the same effect as when switching to a user nobody, but stronger if possible. That is, I want my C application to do the following:

  • Run as a normal user, and not rootwithout the setuid file permission bit
  • Keep the ability to access certain files and open outgoing network connections.
  • Freely and constantly lose their ability to read and write files in the specified (or all) directories, especially $HOME
  • If possible, give up all other non-essential abilities, for example, open the listening socket with accept

Things I have reviewed so far that do not match the score:

  • Switch to user nobodyusing setuid/setgid
    • Ordinary users are not allowed to switch to other users (for example, nobody), and the application does not rootjust need to switch to nobody.
  • Linux / POSIX.1e features
    • Features only add root-like privileges, and do not remove the usual user privileges.
  • Traditional seccomp
    • My application will require more than just a exit, sigreturn, readandwrite

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