linux-kernel - Re: [PATCH 00/14] run seccomp after ptrace

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Date:	Mon, 13 Jun 2016 13:50:57 -0700
From:	Kees Cook <keescook@...omium.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Chris Metcalf <cmetcalf@...lanox.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Helge Deller <deller@....de>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	James Hogan <james.hogan@...tec.com>,
	Jeff Dike <jdike@...toit.com>,
	linux-arch <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	linux-parisc <linux-parisc@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"Maciej W. Rozycki" <macro@...tec.com>,
	Mark Rutland <mark.rutland@....com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Richard Weinberger <richard@....at>,
	Russell King <linux@...linux.org.uk>,
	user-mode-linux-devel@...ts.sourceforge.net,
	Will Deacon <will.deacon@....com>,
	"x86@...nel.org" <x86@...nel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 00/14] run seccomp after ptrace

(Oops, forgot to send this series through the lsm list...)

On Thu, Jun 9, 2016 at 2:01 PM, Kees Cook <keescook@...omium.org> wrote:
> There has been a long-standing (and documented) issue with seccomp
> where ptrace can be used to change a syscall out from under seccomp.
> This is a problem for containers and other wider seccomp filtered
> environments where ptrace needs to remain available, as it allows
> for an escape of the seccomp filter.
>
> Since the ptrace attack surface is available for any allowed syscall,
> moving seccomp after ptrace doesn't increase the actually available
> attack surface. And this actually improves tracing since, for
> example, tracers will be notified of syscall entry before seccomp
> sends a SIGSYS, which makes debugging filters much easier.
>
> The per-architecture changes do make one (hopefully small)
> semantic change, which is that since ptrace comes first, it may
> request a syscall be skipped. Running seccomp after this doesn't
> make sense, so if ptrace wants to skip a syscall, it will bail
> out early similarly to how seccomp was. This means that skipped
> syscalls will not be fed through audit, though that likely means
> we're actually avoiding noise this way.
>
> This series first cleans up seccomp to remove the now unneeded
> two-phase entry, fixes the SECCOMP_RET_TRACE hole (same as the
> ptrace hole above), and then reorders seccomp after ptrace on
> each architecture.

Has anyone else had a chance to review this series? I'd like to get it
landed in -next as early as possible in case there are unexpected
problems...

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security