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 21:30:11 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Amir Goldstein <amir73il@...il.com>
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 10.01.2017 21:11, Amir Goldstein wrote:
> 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.

Too complicated for me. Let's drop it unconditionally. See v2 patch.

>
>
>>> 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.
>


-- 
Konstantin