linux-kernel - Re: [PATCH 3/6] ebpf: add a way to dump an eBPF program

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 9 Sep 2015 17:44:06 -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>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Cyrill Gorcunov <gorcunov@...allels.com>
Subject: Re: [PATCH 3/6] ebpf: add a way to dump an eBPF program

On Wed, Sep 9, 2015 at 5:13 PM, Tycho Andersen
<tycho.andersen@...onical.com> wrote:
> On Wed, Sep 09, 2015 at 04:44:24PM -0700, Andy Lutomirski wrote:
>> On Wed, Sep 9, 2015 at 3:34 PM, Tycho Andersen
>> <tycho.andersen@...onical.com> wrote:
>> >
>> > Here's a thought,
>> >
>> > The set I'm currently proposing effectively separates the ref-counting
>> > of the struct seccomp_filter from the struct bpf_prog (by necessity,
>> > since we're referring to filters from fds). What if we went a little
>> > futher, and made a copy of each seccomp_filter on fork(), keeping it
>> > pointed at the same bpf_prog but adding some metadata about how it was
>> > inherited (tsk->seccomp.filter->inheritence_count++ perhaps). This
>> > would still require this change:
>>
>> Won't that break the tsync mechanism?
>
> We'll need the change I posted (is_ancestor comparing the underlying
> bpf_prog instead of the seccomp_filter), but then I think it'll work.
> I guess we'll need to do some more bookkeeping when we install filters
> via TSYNC since each thread would need its own seccomp_filter, and
> we'd also have to decide whether a filter installed via TSYNC was
> inherited or not.
>
> Am I missing something?

Yes.  I don't think that:

int fd = [create an ebpf fd];
if (fork()) {
  /* Process A */
  seccomp(attach fd);
  ...
} else {
  /* Process B */
  seccomp(attach fd);
  ...
}

should result in processes A and B being considered to have the same
seccomp_filter state.  In particular, I eventually want to make the
seccomp_filter state be considerably more interesting than just the
bpf program.

IOW I really do think that seccomp_filter should have identity.

There's another severe problem, I think.  Suppose that ebpf1 and ebpf2
are ebpf fds.  If processes C and D start out with no filters at all,
C attaches ebpf1 and ebpf2, and D attaches just ebpf2, then C and D
are definitely *not* in the same state, and neither is an ancestor of
the other.

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/