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

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Date:   Thu, 7 Nov 2019 08:45:55 +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 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).

Colin

> 
> Thanks,
> Amir.
>