linux-kernel - Re: vfs / overlayfs conflict resolution for linux-next

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Date:   Wed, 18 Jul 2018 13:43:40 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: vfs / overlayfs conflict resolution for linux-next

On Wed, Jul 18, 2018 at 02:10:32PM +0200, Miklos Szeredi wrote:
> On Wed, Jul 18, 2018 at 9:25 AM, Miklos Szeredi <mszeredi@...hat.com> wrote:
> > On Wed, Jul 18, 2018 at 5:29 AM, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> >> Hi Al,
> >>
> >> On Wed, 18 Jul 2018 03:56:37 +0100 Al Viro <viro@...IV.linux.org.uk> wrote:
> >>>
> >>> ... and now it even builds.  Said that, I would really like to hear something
> >>> from you - I can duplicate the entire overlayfs-next and merge it into
> >>> my #for-next and ask Steven to use that instead of your tree, but I very
> >>> much dislike going over your head like that.
> >>>
> >>> I realize that you'd been away for a while and probably are digging yourself
> >>> from under the piles of mail, but it's getting late in the cycle and I want
> >>> to get #for-next into reasonably sane shape.  Please, look through that
> >>> thing and respond.
> 
> In "ovl: stack file ops" this:
> 
>     AV: make it use open_with_fake_path(), don't mess with override_creds
> 
> Maybe it's the way to go, but looks broken as is; e.g. NFS does call
> current_creds() from its open method to get the credentials to work
> with.

It *is* broken.  For now leave override_creds() as in your variant, but
we really want to deal with that crap eventually.

> Okay, so ->open() is a file op, and file ops should use file->f_cred,
> but how are we going to enforce this?

I'd say we cut down on the use of current_cred() when deep in call chain...