linux-kernel - Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering

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Date:	Thu, 26 May 2011 10:17:09 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Will Drewry <wad@...omium.org>
Cc:	Colin Walters <walters@...bum.org>,
	Kees Cook <kees.cook@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, James Morris <jmorris@...ei.org>
Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering

On Thu, May 26, 2011 at 10:02 AM, Will Drewry <wad@...omium.org> wrote:
>
> Absolutely - that was what I meant :/  The patches do not currently
> check creds at creation or again at use, which would lead to
> unprivileged filters being used in a privileged context.  Right now,
> though, if setuid() is not allowed by the seccomp-filter, the process
> will be immediately killed with do_exit(SIGKILL) on call -- thus
> avoiding a silent failure.

Umm.

You do realize that there is a reason we don't allow random kill()
system calls to succeed without privileges either?

So no, "we kill it with sigkill" is not safe *either*. It now is
potentially a way to kill privileged processes that you didn't have
permission to kill.

My point is that it all sounds designed for well-behaved processes.
"kill it if it does something bad" sounds like a *wonderful* idea if
you're doing a sandbox.

But it is suddenly potentially deadly if that capability is used by a
malicious user for a process that isn't ready for it.

One option is to just not ever allow execve() from inside a restricted
environment.

                       Linus
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