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

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Date:	Wed, 16 Mar 2011 22:23:30 +0100
From:	Richard Weinberger <richard@....at>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Arnd Bergmann <arnd@...db.de>, 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/

Am Mittwoch 16 März 2011, 22:17:39 schrieb Eric W. Biederman:
> Richard Weinberger <richard@....at> writes:
> 
> 2> Am Mittwoch 16 März 2011, 21:45:45 schrieb Arnd Bergmann:
> >> On Wednesday 16 March 2011 21:08:16 Richard Weinberger wrote:
> >> > Am Mittwoch 16 März 2011, 20:55:49 schrieb Kees Cook:
> >> > > 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...
> >> 
> >> How does this interact with the per-namespace sysctls that Eric
> >> Biederman added a few years ago?
> > 
> > Do you mean CONFIG_{UTS, UPC, USER, NET,}_NS?
> > 
> >> I had expected that any dangerous sysctl would not be visible in
> >> an unpriviledge container anyway.
> > 
> > No way.
> > That's why it's currently a very good idea to mount /proc/ read-only
> > into a container.
> 
> However it is in the architecture.  The problem is that the user
> namespace is not finished.  Once finished even root with all caps in a
> container will have no more permissions than the unprivileged user that
> created the user namespace.
> 
> Essentially the change is to make permissions checks become a comparison
> of the tuple (user_ns, uid) instead of just comparisons by uid.  If we
> want to fix permission problems with proc and containers please let's
> focus on the completing the user namespace.

Ok. What's the current status, where can I help?

> Eric

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