From: Richard Weinberger <richard@nod.at>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH] [RFC] Make it easier to harden /proc/
Date: Wed, 16 Mar 2011 22:23:30 +0100
User-Agent: KMail/1.13.5 (Linux/2.6.25.20-0.7-pae; KDE/4.4.4; i686; ; )
Cc: Arnd Bergmann <arnd@arndb.de>, Kees Cook <kees.cook@canonical.com>,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        serge@hallyn.com, eparis@redhat.com, jmorris@namei.org,
        eugeneteo@kernel.org, drosenberg@vsecurity.com
References: <1300303907-22627-1-git-send-email-richard@nod.at> <201103162152.49615.richard@nod.at> <m1lj0eepe4.fsf@fess.ebiederm.org>
In-Reply-To: <m1lj0eepe4.fsf@fess.ebiederm.org>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="utf-8"
Content-Transfer-Encoding: 8BIT
Message-Id: <201103162223.30997.richard@nod.at>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2578
Lines: 59

Am Mittwoch 16 März 2011, 22:17:39 schrieb Eric W. Biederman:
> Richard Weinberger <richard@nod.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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/