linux-kernel - Re: [PATCH] cgroup: fix device deny of DEV

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Date:	Tue, 22 May 2012 08:34:34 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Serge Hallyn <serge.hallyn@...onical.com>
Cc:	Amos Kong <akong@...hat.com>,
	containers@...ts.linux-foundation.org, mtosatti@...hat.com,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	tj@...nel.org
Subject: Re: [PATCH] cgroup: fix device deny of DEV_ALL

Serge Hallyn wrote:

> Quoting Amos Kong (akong@...hat.com):
>> @ mount -t cgroup -o devices none /cgroup
>> @ mkdir /cgroups/devices
>> @ ls -l /dev/dm-3
>>  brw-rw----. 1 root disk 253, 3 Oct 14 19:03 /dev/dm-3
>> @ echo 'b 253:3 rw' > devices.deny
>> but I can still write it by 'dd if=/dev/zero of=/dev/dm-3'
>>
>> In devcgroup_create(), we create a new whitelist, and add first
>> entry which type is 'DEV_ALL'. Execute "# echo 'b 253:3 rw' >
>> devices.deny", dev_whitelist_rm() will update access of first
>> entry to 1(m), but type of first entry is still 'DEV_ALL'.
> 
> Hi,
> 
> thanks.  You raise a good point, but I think it needs some discussion.
> 
> What happens right now is that if you have the 'a *:* rwm' entry and do
> echo 'b 253:3 rw' > devices.deny, then when you next cat devices.list you
> will still see the 'a *:* rwm' entry.  So there should be no confusion
> over why the dd succeeds.  You didn't remove the entry, because there
> was no match echoed into devices.deny.


No, you'll see the entry has been changed to 'a *:* m', so I think we
should at least fix this.
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