Re: [PATCH v5 2/3] seccomp_filters: system call filtering using BPF

[Andrew Lutomirski]

On Fri, Jan 27, 2012 at 3:24 PM, Will Drewry <wad@xxxxxxxxxxxx> wrote:
> Filter programs will be inherited across fork/clone and execve.
> However, if the task attaching the filter is unprivileged
> (!CAP_SYS_ADMIN) the no_new_privs bit will be set on the task.  This
> ensures that unprivileged tasks cannot attach filters that affect
> privileged tasks (e.g., setuid binary).

This makes me nervous -- I don't think that the behavior of any new
API should be different depending on privilege level -- adding a
privilege should just make things work that would otherwise fail.  You
might end up with bugs where a program is completely safe if run
without CAP_SYS_ADMIN but, if run with CAP_SYS_ADMIN, bad things
happen.  (The behavior of setuid(geteuid()) is an example of this
problem.)

One way to fix it is to make setting a filter program fail unless
capable(CAP_SYS_ADMIN ) || no_new_privs.

--Andy
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