linux-kernel - Re: [PATCH] ovl: create UUIDs for file systems that do not set the superblock UUID

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Message-ID: <bba96a64-a9f7-cd03-e00b-8ee369520ae7@canonical.com>
Date:   Thu, 7 Nov 2019 09:43:59 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ovl: create UUIDs for file systems that do not set the
 superblock UUID

On 07/11/2019 09:12, Colin Ian King wrote:
> On 07/11/2019 08:45, Colin Ian King wrote:
>> On 07/11/2019 07:08, Amir Goldstein wrote:
>>> On Thu, Nov 7, 2019 at 1:43 AM Colin King <colin.king@...onical.com> wrote:
>>>>
>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>
>>>> Some file systems such as squashfs do not set the UUID in the
>>>> superblock resulting in a zero'd UUID.  In cases were two or more
>>>> of these file systems are overlayed on the lower layer we can hit
>>>> overlay corruption issues because identical zero'd overlayfs UUIDs
>>>> are impossible to differentiate between.  This can be fixed by
>>>> creating an overlayfs UUID based on the file system from the
>>>> superblock s_magic and s_dev fields.  (This currently seems like
>>>> enough information to be able create a UUID, but the could be
>>>> scope to use other super block fields such as the pointer s_fs_info
>>>> but may need some obfuscation).
>>>>
>>>
>>> The fix is incorrent. uuid stored in xattr needs to have persistent properties.
>>> In the use case that you describe, the origin file handle should simply be
>>> ignored.
>>>
>>> Please test attached patch.
>>
>> Thanks for the patch. Tested, and the error still occurs:
>>
>> [  163.959633] overlayfs: invalid origin (etc/.pwd.lock, ftype=8000,
>> origin ftype=4000).
> 
> Added debug, seems like nouuid is not being set to true, nouuid is false
> on the layers 0 and 1.

So nouuid is not being set in ovl_lower_uuid_ok() because the code is
returning early because of the following statement:

if (!ofs->config.nfs_export && !(ofs->config.index && ofs->upper_mnt))
	return true;

..and not getting to the following for-loop.

> 
>>
>> Colin
>>
>>>
>>> Thanks,
>>> Amir.
>>>
>>
>