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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Wed, 9 Dec 2020 20:16:10 +0200
Message-ID: <CAOQ4uxjDEVnz3Y_BqH41J4+E5dWRPyut_VPokEeMBNALx9oQhw@mail.gmail.com>
Subject: Re: [PATCH v2 03/10] ovl: check privs before decoding file handle
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Miklos Szeredi <mszeredi@redhat.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, Dec 9, 2020 at 6:20 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Wed, Dec 9, 2020 at 11:13 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> > Hard link indexing should work without fh decoding, since it is only
> > encoding the file handle to search for the index entry, and encoding
> > is not privileged.
>
> Tested this a bit and while hard link indexing does work,  inode
> lookup is broken since it uses the origin inode as a key (which is not

Yes, that is what I meant by ovl_check_origin() is broken.

> available) instead of using the origin value directly.  This is
> fixable, but needs a fair amount of restructuring, so let's just

Maybe it also requires on-disk changes.
We should be able to use the origin fh as the key for lower inode,
but we need the lower st_inode for initializing the ovl inode with
correct ino. If we cannot decode lower inode from origin fh, I think
we would need to store the ino in user.overlay.ino on copy up or
maintain redirect, but redirect is not supported either with user ns mount...

> postpone this and disable index for now, as you suggested.
>

Nobody seems to be enabling it anyway :-/

Thanks,
Amir.