linux-kernel - Re: [PATCH] [RFC] Make it easier to harden /proc/

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Date:	Wed, 16 Mar 2011 23:19:11 +0200
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	Kees Cook <kees.cook@...onical.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, serge@...lyn.com, eparis@...hat.com,
	jmorris@...ei.org, eugeneteo@...nel.org, drosenberg@...curity.com
Subject: Re: [PATCH] [RFC] Make it easier to harden /proc/

On Wed, Mar 16, 2011 at 09:08:16PM +0100, Richard Weinberger wrote:
> Kees,
> 
> Am Mittwoch 16 März 2011, 20:55:49 schrieb Kees Cook:
> > Hi Richard,
> > 
> > On Wed, Mar 16, 2011 at 08:31:47PM +0100, Richard Weinberger wrote:
> > > When containers like LXC are used a unprivileged and jailed
> > > root user can still write to critical files in /proc/.
> > > E.g: /proc/sys/kernel/{sysrq, panic, panic_on_oops, ... }
> > > 
> > > This new restricted attribute makes it possible to protect such
> > > files. When restricted is set to true root needs CAP_SYS_ADMIN
> > > to into the file.
> > 
> > I was thinking about this too. I'd prefer more fine-grained control
> > in this area, since some sysctl entries aren't strictly controlled by
> > CAP_SYS_ADMIN (e.g. mmap_min_addr is already checking CAP_SYS_RAWIO).
> > 
> > How about this instead?
> 
> Good Idea.
> May we should also consider a per-directory restriction.
> Every file in /proc/sys/{kernel/, vm/, fs/, dev/} needs a protection.
> It would be much easier to set the protection on the parent directory
> instead of protecting file by file...

Of course, not.

You should _enable_ them one by one, not the other way around.

	"default deny"
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