MEDIUM: init: set NO_NEW_PRIVS by default when supported

HAProxy doesn't need to call executables at run time (except when using
external checks which are strongly recommended against), and is even expected
to isolate itself into an empty chroot. As such, there basically is no valid
reason to allow a setuid executable to be called without the user being fully
aware of the risks. In a situation where haproxy would need to call external
checks and/or disable chroot, exploiting a vulnerability in a library or in
haproxy itself could lead to the execution of an external program. On Linux
it is possible to lock the process so that any setuid bit present on such an
executable is ignored. This significantly reduces the risk of privilege
escalation in such a situation. This is what haproxy does by default. In case
this causes a problem to an external check (for example one which would need
the "ping" command), then it is possible to disable this protection by
explicitly adding this directive in the global section. If enabled, it is
possible to turn it back off by prefixing it with the "no" keyword.

Before the option:

  $ socat - /tmp/sock1 <<< "expert-mode on; debug dev exec sudo /bin/id"
  uid=0(root) gid=0(root) groups=0(root

After the option:
  $ socat - /tmp/sock1 <<< "expert-mode on; debug dev exec sudo /bin/id"
  sudo: effective uid is not 0, is /usr/bin/sudo on a file system with the
        'nosuid' option set or an NFS file system without root privileges?
4 files changed