Re: [PATCH v3 2/5] seccomp: add the concept of a seccomp filter FD
From: Andy Lutomirski
Date: Wed Sep 30 2015 - 14:47:53 EST
On Wed, Sep 30, 2015 at 11:36 AM, Tycho Andersen
> On Wed, Sep 30, 2015 at 11:27:34AM -0700, Andy Lutomirski wrote:
>> On Wed, Sep 30, 2015 at 11:13 AM, Tycho Andersen
>> <tycho.andersen@xxxxxxxxxxxxx> 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.
> Allowing people doing SECCOMP_FD_NEW to specify a parent fd would
> work. Then we can disallow installing a seccomp fd if its parent is
> not the current filter, and get rid of the whole mess with prev
> locking and all that.
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