Message-ID: <476724E3.6060901@cs.columbia.edu>
Date: Mon, 17 Dec 2007 20:39:47 -0500
From: Oren Laadan <orenl@cs.columbia.edu>
Organization: Columbia University
User-Agent: Thunderbird 2.0.0.9 (X11/20071031)
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To: "Serge E. Hallyn" <serue@us.ibm.com>
CC: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
       linux-fsdevel@vger.kernel.org,
       Linux Containers <containers@lists.osdl.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.
References: <20071216080441.435456586@I-love.SAKURA.ne.jp>	<20071216080628.061470932@I-love.SAKURA.ne.jp>	<200712161944.HEI26071.MOtOFLVHFSQFOJ@I-love.SAKURA.ne.jp>	<200712161956.BJE32406.FOOHtQJLMFOSVF@I-love.SAKURA.ne.jp>	<20071217194802.GA14156@sergelap.austin.ibm.com>	<200712180003.lBI03N7F092396@www262.sakura.ne.jp> <20071218003955.GA27048@sergelap.austin.ibm.com>
In-Reply-To: <20071218003955.GA27048@sergelap.austin.ibm.com>
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I hate to bring this again, but what if the admin in the container
mounts an external file system (eg. nfs, usb, loop mount from a file,
or via fuse), and that file system already has a device that we would
like to ban inside that container ?

Since anyway we will have to keep a white- (or black-) list of devices
that are permitted in a container, and that list may change even change
per container -- why not enforce the access control at the VFS layer ?
It's safer in the long run.

Oren.

Serge E. Hallyn wrote:
> Quoting Tetsuo Handa (penguin-kernel@i-love.sakura.ne.jp):
>> Hello.
>>
>> Serge E. Hallyn wrote:
>>> CAP_MKNOD will be removed from its capability
>> I think it is not enough because the root can rename/unlink device files
>> (mv /dev/sda1 /dev/tmp; mv /dev/sda2 /dev/sda1; mv /dev/tmp /dev/sda2).
> 
> Sure but that doesn't bother us :)
> 
> The admin in the container has his own /dev directory and can do what he
> likes with the devices he's allowed to have.  He just shouldn't have
> access to others.  If he wants to rename /dev/sda1 to /dev/sda5 that's
> his choice.
> 
>>> To use your approach, i guess we would have to use selinux (or tomoyo)
>>> to enforce that devices may only be created under /dev?
>> Everyone can use this filesystem alone.
> 
> Sure but it is worthless alone.
> 
> No?
> 
> What will keep the container admin from doing 'mknod /root/hda1 b 3 1'?
> 
>> But use with MAC (or whatever access control mechanisms that prevent
>> attackers from unmounting/overlaying this filesystem) is recomennded.
> 
> -serge
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/containers
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