request: capabilities that allow users to drop privileges further

[Felix von Leitner <felix-kernel@fefe.de>]

I would like to be able to drop capabilities that every normal user has,
so that network servers can limit the impact of possible future security
problems further.  For example, I want my non-cgi web server to be able
to drop the capabilities to

  * fork
  * execve
  * ptrace
  * load kernel modules
  * mknod
  * write to the file system

and I would like to modify my smtpd to not be able to

  * fork
  * execve
  * ptrace
  * load kernel modules
  * mknod

I can kludge around some of these, for example I can disable fork with
resource limits, and I can limit writing to the file system with chroot
and proper permissions in the file systems, but I'm not aware of a way
to disable ptrace for example, or pthread_create.

I know that there are patches to provide an extended "jail" chroot
support, but being able to drop capabilities like this would be a more
general solution.

Felix