linux-kernel - Re: [PATCH] ovl: do not ignore disk quota if current task is not privileged

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Date:   Tue, 10 Jan 2017 19:44:27 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-unionfs@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>
Subject: Re: [PATCH] ovl: do not ignore disk quota if current task is not
 privileged

On 10.01.2017 19:35, Vivek Goyal wrote:
> On Tue, Jan 10, 2017 at 11:06:47AM -0500, Vivek Goyal wrote:
>> On Tue, Jan 10, 2017 at 02:26:48PM +0300, Konstantin Khlebnikov wrote:
>>> If overlay was mounted by root then quota set for upper layer does not work
>>> because overlay now always use mounter's credentials for operations.
>>>
>>
>> Hi Konstantin,
>>
>> So CAP_SYS_RESOURCE bypasses the quota checks?
>>
>> I just created dir upper on xfs filesystem and defined quota of 1G and
>> as root user (with cap_sys_resoureces), I am not able to create file
>> bigger than 1g in that dir. So looks like xfs quota took affect even
>> for privileged user with CAP_SYS_RESOURCE set.
>>
>> What am I missing?
>
> As root user, I set limit of 1G on work/ and upper/ dir and created
> a file of 4G in lower/ dir and mounted overlay on "merged" dir and
> did "touch zerofile", and go error message.
>
> touch: cannot touch 'zerofile': No space left on device
>
> So looks like I am doing something wrong and not be able to reproduce
> the issue to begin with.
>

I'm using ext4 project quota around upper/work directories.
ext4 use generic quota implementation: it ignores hard limits if CAP_SYS_RESOURCE is set.

It seems XFS ignores CAP_SYS_RESOURCE for any kind of quota.
But I've found special meaning for CAP_FOWNER - chown() can ignore user/group
quota if caller have this capability.

-- 
Konstantin