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 20:11:50 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        Vivek Goyal <vgoyal@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>
Subject: Re: [PATCH] ovl: do not ignore disk quota if current task is not privileged

On Tue, Jan 10, 2017 at 6:34 PM, Konstantin Khlebnikov
<khlebnikov@...dex-team.ru> wrote:
>
> On 10.01.2017 18:57, Miklos Szeredi wrote:
>>
>> On Tue, Jan 10, 2017 at 3:46 PM, Vivek Goyal <vgoyal@...hat.com> 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.
>>>>
>>>> This patch adds second copy of credentials without CAP_SYS_RESOURCE and
>>>> use it if current task doesn't have this capability in mounter's user-ns.
>>>> This affects creation new files, whiteouts, and copy-up operations.
>>>>
>>>> Now quota limits are ignored only if both mounter and current task have
>>>> capability CAP_SYS_RESOURCE in root user namespace.
>>>
>>>
>>> This makes sense to me. I too would like quota to take effect for
>>> containers on overlay.
>>
>>
>> At first sight I hated this patch.  It breaks the nice concept that
>> underlying filesystems are just storage for the overlay and don't care
>> about caller's privileges (as a block device wouldn't care about
>> caller's privileges when allocating space).
>>
>> However I don't see a good way around this, so...
>
>
> Another solution: just always drop CAP_SYS_RESOURCE from capabilities.
>

That sounds like a better (and simpler) solution.

Let overlayfs support mount options noquota|quota (default configurable
from Kconfig and module param) and 'quota' means drop CAP_SYS_RESOURCE.


>> Looks like this also has effect on reserving space in ext4, not sure
>> what that entails.
>
>
> Yes, CAP_SYS_RESOURCE allows to use reserved space and inodes.
>

That's really not good. It's beyond disobeying user quotas, because
file system may get to unrecoverable state when corruption is detected
and already filled the root reserved space.

Amir.