linux-kernel - Re: [PATCH v3 2/5] seccomp: add the concept of a seccomp filter FD

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Message-ID: <CALCETrXkG6QCx9ptyN+VWrjgoTvwZAOfa-pWhS4iCZ=fpm6YnQ@mail.gmail.com>
Date:	Wed, 30 Sep 2015 11:27:34 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Tycho Andersen <tycho.andersen@...onical.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3 2/5] seccomp: add the concept of a seccomp filter FD

On Wed, Sep 30, 2015 at 11:13 AM, Tycho Andersen
<tycho.andersen@...onical.com> wrote:
> This patch introduces the concept of a seccomp fd, with a similar interface
> and usage to ebpf fds. Initially, one is allowed to create, install, and
> dump these fds. Any manipulation of seccomp fds requires users to be root
> in their own user namespace, matching the checks done for
> SECCOMP_SET_MODE_FILTER.
>
> Installing a filterfd has some gotchas, though. Andy mentioned previously
> that we should restrict installation to filter fds whose parent is already
> in the filter tree. This doesn't quite work in the case of created seccomp
> fds, since once you install a filter fd, you can't install any other filter
> fd since it has no parent and there is no way to "pre-chain" filters before
> installing them.

ISTM, if we like the seccomp fd approach, we should have them be
created with a parent already set.  IOW the default should be that
their parent is the creator's seccomp fd and, if needed, creators
could specify a different parent.

--Andy
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