From: Richard Weinberger <richard@nod.at>
To: Alexey Dobriyan <adobriyan@gmail.com>
Subject: Re: [PATCH] [RFC] Make it easier to harden /proc/
Date: Wed, 16 Mar 2011 22:07:48 +0100
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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,
        "Eric W. Biederman" <ebiederm@xmission.com>
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In-Reply-To: <20110316210452.GA13624@p183.telecom.by>
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Am Mittwoch 16 M?rz 2011, 22:04:52 schrieb Alexey Dobriyan:
> On Wed, Mar 16, 2011 at 09:52:49PM +0100, Richard Weinberger wrote:
> > Am Mittwoch 16 M?rz 2011, 21:45:45 schrieb Arnd Bergmann:
> > > On Wednesday 16 March 2011 21:08:16 Richard Weinberger wrote:
> > > > Am Mittwoch 16 M?rz 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?
> 
> It only covers /proc/sys/net/

Exactly.

> > > I had expected that any dangerous sysctl would not be visible in
> > > an unpriviledge container anyway.
> > 
> > No way.
> 
> No way what exactly?

Dangerous sysctls are not protected at all.
E.g. A jailed root can use /proc/sysrq-trigger.

> 
> > That's why it's currently a very good idea to mount /proc/ read-only into
> > a container.

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