From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tycho Andersen Subject: Re: [PATCH v2 2/5] seccomp: make underlying bpf ref counted as well Date: Fri, 11 Sep 2015 08:44:00 -0600 Message-ID: <20150911144400.GI27574@smitten> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Kees Cook , Alexei Starovoitov , "David S. Miller" , Will Drewry , Oleg Nesterov , Andy Lutomirski , Pavel Emelyanov , "Serge E. Hallyn" , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Daniel Borkmann Return-path: Content-Disposition: inline In-Reply-To: <55F2D0EC.9090004-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org 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? Tycho