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

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Message-ID: <CAOQ4uxgj8FO-yqtHsjh2OaTGvcF3HA5OekqiUuZEFE+LGGaTCg@mail.gmail.com>
Date:   Thu, 7 Nov 2019 11:56:33 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Colin Ian King <colin.king@...onical.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>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] ovl: create UUIDs for file systems that do not set the
 superblock UUID

On Thu, Nov 7, 2019 at 11:44 AM Colin Ian King <colin.king@...onical.com> wrote:
>
> 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.
>

Indeed. I had this bit of information in my mind for a brief moment
and forgot about it..

Please remove this optimization and change the call to:

       if (ofs->upper_mnt && !ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
...

Maybe change the language of "falling back to index=off..." to
"enforcing index=off..."

You may then submit the patch with my Signed-off and yours.
Please also change the name nouuid to bad_uuid per Dan's review comment.

Thanks,
Amir.