linux-kernel - Re: cgroup: denying device doesn't work with 'rw' mode string

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Message-ID: <CAFeW=pZ-HZKyBALRZVo=PeWUoaEk39QUSoMsV-1K5CBgcVUMeA@mail.gmail.com>
Date:	Fri, 18 May 2012 11:37:15 +0800
From:	Amos Kong <kongjianjun@...il.com>
To:	serue@...ibm.com, viro@...iv.linux.org.uk
Cc:	linux-kernel@...r.kernel.org, lizf@...fujitsu.com, tj@...nel.org,
	jmorris@...ei.org
Subject: Re: cgroup: denying device doesn't work with 'rw' mode string

CC: Li Zefan <lizf@...fujitsu.com>, Tejun Heo <tj@...nel.org>, jmorris@...ei.org

On Sat, Oct 15, 2011 at 8:39 AM, Amos Kong <kongjianjun@...il.com> wrote:
> # mount -t cgroup -o devices none /cgroup
> # mkdir /cgroups/devices
> # ls -l /dev/vg/lv
> lrwxrwxrwx. 1 root root 7 Oct 14 19:03 /dev/vg/lv -> ../dm-3
> # ls -l /dev/dm-3
> brw-rw----. 1 root disk 253, 3 Oct 14 19:03 /dev/dm-3
>
>
> ------- test1
> deny read-write permission of dm-3, but it doesn't effect.
>
> # echo a > devices/devices.allow
> # echo 'b 253:2 rw' > devices.deny
>                ^^
> # echo $$ > task
> # dd if=/dev/zero of=/dev/dm-3 bs=1M count=1
> can write to /dev/dm-3 successfully  (problem exists)
>
> ------- test2
> # echo a > devices/devices.allow
> # echo 'b 253:3 rwm' > devices/devices.deny
>                ^^^
> # echo $$ > task
> # dd if=/dev/zero of=/dev/dm-3 bs=1M count=1
> couldn't write to /dev/dm-3 successfully
>
> -----------
>
> related upstream commit:
> commit 08ce5f16ee466ffc5bf243800deeecd77d9eaf50
> Author: Serge E. Hallyn <serue@...ibm.com>
> Date:   Tue Apr 29 01:00:10 2008 -0700
>
>    cgroups: implement device whitelist
>
>
> cgroup tracks and enforces open and mknod restrictions on device files,
> so 'm' are always needed in the mode string? 'rw' is ineffective?
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