linux-kernel - Re: [PATCH 05/14] seccomp: recheck the syscall after RET

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Date:	Thu, 9 Jun 2016 15:46:10 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Kees Cook <keescook@...omium.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	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@...r.kernel.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" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	Will Deacon <will.deacon@....com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 05/14] seccomp: recheck the syscall after RET_TRACE

On Thu, Jun 9, 2016 at 2:01 PM, Kees Cook <keescook@...omium.org> wrote:
> When RET_TRACE triggers, a tracer may change a syscall into something that
> should be filtered by seccomp. This re-runs seccomp after a trace event
> to make sure things continue to pass.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> ---
>  kernel/seccomp.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 14a37d71b612..54d15eb2b701 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -556,7 +556,8 @@ void secure_computing_strict(int this_syscall)
>  #else
>
>  #ifdef CONFIG_SECCOMP_FILTER
> -static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
> +static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
> +                           const bool recheck_after_trace)

This patch looks good with one minor nit: I read this as "pass true if
you want to recheck after trace", which is exactly the opposite of how
it works.

--Andy