From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753616AbbIKQEP (ORCPT ); Fri, 11 Sep 2015 12:04:15 -0400 Received: from www62.your-server.de ([213.133.104.62]:51221 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753020AbbIKQEN (ORCPT ); Fri, 11 Sep 2015 12:04:13 -0400 Message-ID: <55F2FB6F.7050708@iogearbox.net> Date: Fri, 11 Sep 2015 18:03:59 +0200 From: Daniel Borkmann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Tycho Andersen CC: Kees Cook , Alexei Starovoitov , "David S. Miller" , Will Drewry , Oleg Nesterov , Andy Lutomirski , Pavel Emelyanov , "Serge E. Hallyn" , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH v2 2/5] seccomp: make underlying bpf ref counted as well References: <1441930862-14347-1-git-send-email-tycho.andersen@canonical.com> <1441930862-14347-3-git-send-email-tycho.andersen@canonical.com> <55F2D0EC.9090004@iogearbox.net> <20150911144400.GI27574@smitten> In-Reply-To: <20150911144400.GI27574@smitten> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/11/2015 04:44 PM, Tycho Andersen wrote: > On Fri, Sep 11, 2015 at 03:02:36PM +0200, Daniel Borkmann wrote: >> On 09/11/2015 02:20 AM, Tycho Andersen wrote: >>> In the next patch, we're going to add a way to access the underlying >>> filters via bpf fds. This means that we need to ref-count both the >>> struct seccomp_filter objects and the struct bpf_prog objects separately, >>> in case a process dies but a filter is still referred to by another >>> process. >>> >>> Additionally, we mark classic converted seccomp filters as seccomp eBPF >>> programs, since they are a subset of what is supported in seccomp eBPF. >>> >>> Signed-off-by: Tycho Andersen >>> CC: Kees Cook >>> CC: Will Drewry >>> CC: Oleg Nesterov >>> CC: Andy Lutomirski >>> CC: Pavel Emelyanov >>> CC: Serge E. Hallyn >>> CC: Alexei Starovoitov >>> CC: Daniel Borkmann >>> --- >>> kernel/seccomp.c | 4 +++- >>> 1 file changed, 3 insertions(+), 1 deletion(-) >>> >>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c >>> index 245df6b..afaeddf 100644 >>> --- a/kernel/seccomp.c >>> +++ b/kernel/seccomp.c >>> @@ -378,6 +378,8 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) >>> } >>> >>> atomic_set(&sfilter->usage, 1); >>> + atomic_set(&sfilter->prog->aux->refcnt, 1); >>> + sfilter->prog->type = BPF_PROG_TYPE_SECCOMP; >> >> So, if you do this, then this breaks the assumption of eBPF JITs >> that, currently, all classic converted BPF programs always have a >> prog->type of BPF_PROG_TYPE_UNSPEC (see: bpf_prog_was_classic()). >> >> Currently, JITs make use of this information to determine whether >> A and X mappings for such programs should or should not be cleared >> in the prologue (s390 currently). >> >> In the seccomp_prepare_filter() stage, we're already past that, so >> it will not cause an issue, but we certainly would need to be very >> careful in future, if bpf_prog_was_classic() is then used at a later >> stage when we already have a generated bpf_prog somewhere, as then >> this assumption will break. > > The only reason we need to do this is to allow BPF_DUMP_PROG to work, > since we were restricting it to only allow dumping of seccomp > programs, since those don't have maps. Instead, perhaps we could allow > dumping of BPF_PROG_TYPE_SECCOMP and BPF_PROG_TYPE_UNSPEC? There are possibilities that BPF_PROG_TYPE_UNSPEC is calling helpers already today, at least in networking case, not seccomp. So, since you want to export [classic -> eBPF] only for seccomp, put fds on them and dump these via bpf(2), you could allow that (with a big comment stating why it's safe), but mid-term we really need to sanitize all this stuff properly as this is needed for other types, too.