From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755769AbbCLUBw (ORCPT ); Thu, 12 Mar 2015 16:01:52 -0400 Received: from mail-la0-f46.google.com ([209.85.215.46]:38520 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754162AbbCLUBt (ORCPT ); Thu, 12 Mar 2015 16:01:49 -0400 From: Mikael Pettersson X-Google-Original-From: "Mikael Pettersson" MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <21761.61606.624750.9745@gargle.gargle.HOWL> Date: Thu, 12 Mar 2015 21:01:42 +0100 To: Jann Horn Cc: Michael Kerrisk , Mikael Pettersson , linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Russell King , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Jeff Dike , Richard Weinberger , Kees Cook , Andy Lutomirski , Will Drewry Subject: Re: [PATCH] seccomp.2: Add note about alarm(2) not being sufficient to limit runtime In-Reply-To: <20150312130701.GA11073@pc.thejh.net> References: <20150311174204.GA5712@pc.thejh.net> <21760.46870.338764.599348@gargle.gargle.HOWL> <20150312130701.GA11073@pc.thejh.net> X-Mailer: VM 8.1.2 under 24.3.1 (x86_64-redhat-linux-gnu) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jann Horn writes: > On Wed, Mar 11, 2015 at 10:43:50PM +0100, Mikael Pettersson wrote: > > Jann Horn writes: > > > Or should I throw this patch away and write a patch > > > for the prctl() manpage instead that documents that > > > being able to call sigreturn() implies being able to > > > effectively call sigprocmask(), at least on some > > > architectures like X86? > > > > Well, that is the semantics of sigreturn(). It is essentially > > setcontext() [which includes the actions of sigprocmask()], but > > with restrictions on parameter placement (at least on x86). > > > > You could introduce some setting to restrict that aspect for > > seccomp processes, but you can't change this for normal processes > > without breaking things. > > Then I think it's probably better and easier to just document the existing > behavior? If a new setting would have to be introduced and developers would > need to be aware of that, it's probably easier to just tell everyone to use > SIGKILL. > > Does this manpage patch look good? LGTM Acked-by: Mikael Pettersson > > --- > man2/seccomp.2 | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/man2/seccomp.2 b/man2/seccomp.2 > index 702ceb8..f762d07 100644 > --- a/man2/seccomp.2 > +++ b/man2/seccomp.2 > @@ -64,6 +64,31 @@ Strict secure computing mode is useful for number-crunching > applications that may need to execute untrusted byte code, perhaps > obtained by reading from a pipe or socket. > > +Note that although the calling thread can no longer call > +.BR sigprocmask (2), > +it can use > +.BR sigreturn (2) > +to block all signals apart from > +.BR SIGKILL > +and > +.BR SIGSTOP . > +Therefore, to reliably terminate it, > +.BR SIGKILL > +has to be used, meaning that e.g. > +.BR alarm (2) > +is not sufficient for restricting its runtime. Instead, use > +.BR timer_create (2) > +with > +.BR SIGEV_SIGNAL > +and > +.BR sigev_signo > +set to > +.BR SIGKILL > +or use > +.BR setrlimit (2) > +to set the hard limit for > +.BR RLIMIT_CPU . > + > This operation is available only if the kernel is configured with > .BR CONFIG_SECCOMP > enabled. > -- > 2.1.4 --