linux-kernel - Re: overlayfs vs. fscrypt

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Message-ID: <1854703.ve7plDhYWt@blindfold>
Date:   Wed, 13 Mar 2019 14:00:28 +0100
From:   Richard Weinberger <richard@....at>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: overlayfs vs. fscrypt

Am Mittwoch, 13. März 2019, 13:58:11 CET schrieb Miklos Szeredi:
> On Wed, Mar 13, 2019 at 1:47 PM Richard Weinberger <richard@....at> wrote:
> >
> > Am Mittwoch, 13. März 2019, 13:36:02 CET schrieb Miklos Szeredi:
> > > I don't get it.  Does fscrypt try to check permissions via
> > > ->d_revalidate?  Why is it not doing that via ->permission()?
> >
> > Please let me explain. Suppose we have a fscrypto directory /mnt and
> > I *don't* have the key.
> >
> > When reading the directory contents of /mnt will return an encrypted filename.
> > e.g.
> > # ls /mnt
> > +mcQ46ne5Y8U6JMV9Wdq2C
> 
> Why does showing the encrypted contents make any sense?  It could just
> return -EPERM on all operations?

The use case is that you can delete these files if the DAC/MAC permissions allow it.
Just like on NTFS. If a user encrypts files, the admin cannot read them but can
remove them if the user is gone or loses the key.

Thanks,
//richard