netdev - Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET

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Message-ID: <CAGXu5jLVwYev3EmLOKuEdyaqieGzWgVpFcgodnUbUkbMbiJVqQ@mail.gmail.com>
Date:	Sat, 25 Feb 2012 12:20:13 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
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	mcgrathr@...omium.org, tglx@...utronix.de, luto@....edu,
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	scarybeasts@...il.com, indan@....nu, pmoore@...hat.com,
	akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
	markus@...omium.org, coreyb@...ux.vnet.ibm.com
Subject: Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO

On Fri, Feb 24, 2012 at 7:21 PM, Will Drewry <wad@...omium.org> wrote:
> This change adds the SECCOMP_RET_ERRNO as a valid return value from a
> seccomp filter.  Additionally, it makes the first use of the lower
> 16-bits for storing a filter-supplied errno.  16-bits is more than
> enough for the errno-base.h calls.
>
> Returning errors instead of immediately terminating processes that
> violate seccomp policy allow for broader use of this functionality
> for kernel attack surface reduction.  For example, a linux container
> could maintain a whitelist of pre-existing system calls but drop
> all new ones with errnos.  This would keep a logically static attack
> surface while providing errnos that may allow for graceful failure
> without the downside of do_exit() on a bad call.
>
> v11: - check for NULL filter (keescook@...omium.org)
> v10: - change loaders to fn
>  v9: - n/a
>  v8: - update Kconfig to note new need for syscall_set_return_value.
>     - reordered such that TRAP behavior follows on later.
>     - made the for loop a little less indent-y
>  v7: - introduced
>
> Signed-off-by: Will Drewry <wad@...omium.org>

Reviewed-by: Kees Cook <keescook@...omium.org>

> +       /* Ensure unexpected behavior doesn't result in failing open. */
> +       if (unlikely(current->seccomp.filter == NULL))
> +               ret = SECCOMP_RET_KILL;

Any reason to not just immediately return in this case?

-Kees

-- 
Kees Cook
ChromeOS Security
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