All of lore.kernel.org
 help / color / mirror / Atom feed
From: Miklos Szeredi <miklos@szeredi.hu>
To: Richard Weinberger <richard@nod.at>
Cc: linux-fsdevel@vger.kernel.org, linux-fscrypt@vger.kernel.org,
	overlayfs <linux-unionfs@vger.kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: overlayfs vs. fscrypt
Date: Wed, 13 Mar 2019 13:36:02 +0100	[thread overview]
Message-ID: <CAJfpegsy31D+=VJ+By2a9TLCvZJwvAUpb+_bJ5JVTsmsbZJTKQ@mail.gmail.com> (raw)
In-Reply-To: <4603533.ZIfxmiEf7K@blindfold>

On Wed, Mar 13, 2019 at 1:31 PM Richard Weinberger <richard@nod.at> wrote:
>
> Hi!
>
> overlayfs and fscrypt are not friends.
> Currently it is not possible to use a fscrypt encrypted directory as upper
> directory with overlayfs.
> The reason for that is, fscrypt implements ->d_revalidate().
>
> From fscrypt's point of view having ->d_revalidate() makes sense because it
> wants to hide/show encrypted filenames if someone loads or unlinks a key.
>
> On the other hand, overlayfs makes sure that the upper directory cannot
> change beneath it. Therefore it checks whether the upper directory is a remote
> filesystem by checking for ->d_revalidate() and refuses to mount if so.
>
> In my little embedded Linux world it is common to use both UBIFS and
> overlayfs. Now with UBIFS being encrypted using fscrypt, overlayfs is a
> problem.
> My current hack is not using fscrypt_d_ops in UBIFS. This works because on a
> typical embedded target you setup your crypto keys exactly once, right before
> you mount overlayfs in an initramfs.
>
> But I'm sure this problem will hit sooner or later users of ext4 and f2fs too.
> Therefore I'd like to discuss possible solutions.
>
> So far I see two options:
>
> 1. Get rid of ->d_revalidate() in fscrypt.
> Maybe we find a way to return a dentry via ->lookup() which is not cached at
> all and therefore no ->d_revalidate() is needed. If unreadable and encrypted
> filename lookups are slow, so what?
> AFAIU this approach is impossible in the current dcache design since it is not
> allowed to have more than one dentry to the same file.

I don't get it.  Does fscrypt try to check permissions via
->d_revalidate?  Why is it not doing that via ->permission()?

>
> 2. Teach overlayfs to deal with a upper that has ->d_revalidate().
> Given the complexity of overlayfs I'm not sure how feasible this is.
> But I'm no overlayfs expert, maybe I miss something.

I don't think it would be too complex.  But first I'd like to
understand exactly why fscrypt is (ab) using d_revalidate().

Thanks,
Miklos

  reply	other threads:[~2019-03-13 12:36 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-13 12:31 overlayfs vs. fscrypt Richard Weinberger
2019-03-13 12:31 ` Richard Weinberger
2019-03-13 12:36 ` Miklos Szeredi [this message]
2019-03-13 12:47   ` Richard Weinberger
2019-03-13 12:47     ` Richard Weinberger
2019-03-13 12:58     ` Miklos Szeredi
2019-03-13 13:00       ` Richard Weinberger
2019-03-13 13:00         ` Richard Weinberger
2019-03-13 13:24         ` Miklos Szeredi
2019-03-13 13:32           ` Richard Weinberger
2019-03-13 13:32             ` Richard Weinberger
2019-03-13 14:26             ` Amir Goldstein
2019-03-13 15:16               ` Theodore Ts'o
2019-03-13 15:30                 ` Richard Weinberger
2019-03-13 15:30                   ` Richard Weinberger
2019-03-13 15:36                 ` James Bottomley
2019-03-13 15:51                   ` Eric Biggers
2019-03-13 16:13                     ` James Bottomley
2019-03-13 16:24                       ` Richard Weinberger
2019-03-13 16:44                   ` Theodore Ts'o
2019-03-13 17:45                     ` James Bottomley
2019-03-13 18:58                       ` Theodore Ts'o
2019-03-13 19:17                         ` James Bottomley
2019-03-13 19:57                           ` Eric Biggers
2019-03-13 20:06                             ` James Bottomley
2019-03-13 20:25                               ` Eric Biggers
2019-03-13 21:04                                 ` James Bottomley
2019-03-13 22:13                                   ` Eric Biggers
2019-03-13 22:29                                     ` James Bottomley
2019-03-13 22:58                                       ` Eric Biggers
2019-03-13 16:06                 ` Al Viro
2019-03-13 16:44                   ` Eric Biggers
2019-03-13 19:19                     ` Al Viro
2019-03-13 19:43                       ` Eric Biggers
2019-03-13 15:30               ` Eric Biggers
2019-03-13 15:30                 ` Eric Biggers
2019-03-13 20:33               ` Richard Weinberger
2019-03-13 20:33                 ` Richard Weinberger
2019-03-13 22:26                 ` Eric Biggers
2019-03-13 22:26                   ` Eric Biggers
2019-03-13 22:42                   ` Richard Weinberger
2019-03-14  7:34                     ` Miklos Szeredi
2019-03-14 17:15                       ` [RFC] fscrypt_key_required mount option Richard Weinberger
2019-03-14 17:15                         ` Richard Weinberger
2019-03-14 17:15                         ` [PATCH 1/4] fscrypt: Implement FS_CFLG_OWN_D_OPS Richard Weinberger
2019-03-14 17:15                           ` Richard Weinberger
2019-03-14 17:15                         ` [PATCH 2/4] fscrypt: Export fscrypt_d_ops Richard Weinberger
2019-03-14 17:15                           ` Richard Weinberger
2019-03-14 17:15                         ` [PATCH 3/4] ubifs: Simplify fscrypt_get_encryption_info() error handling Richard Weinberger
2019-03-14 17:15                           ` Richard Weinberger
2019-03-14 17:15                         ` [PATCH 4/4] ubifs: Implement new mount option, fscrypt_key_required Richard Weinberger
2019-03-14 17:15                           ` Richard Weinberger
2019-03-14 17:49                           ` Eric Biggers
2019-03-14 17:49                             ` Eric Biggers
2019-03-14 20:54                             ` Richard Weinberger
2019-03-14 20:54                               ` Richard Weinberger
2019-03-14 23:07                               ` Theodore Ts'o
2019-03-14 23:07                                 ` Theodore Ts'o
2019-03-15  0:26                                 ` Unsubscribe Shane Volpe
2019-03-15  7:48                                 ` [PATCH 4/4] ubifs: Implement new mount option, fscrypt_key_required Richard Weinberger
2019-03-15  7:48                                   ` Richard Weinberger
2019-03-15 13:51                                   ` Theodore Ts'o
2019-03-15 13:51                                     ` Theodore Ts'o
2019-03-15 13:51                                     ` Theodore Ts'o
2019-03-15 13:59                                     ` Richard Weinberger
2019-03-15 13:59                                       ` Richard Weinberger
2019-03-14 23:15                           ` James Bottomley
2019-03-14 23:15                             ` James Bottomley
2019-03-14 23:42                             ` Theodore Ts'o
2019-03-14 23:42                               ` Theodore Ts'o
2019-03-14 23:55                               ` James Bottomley
2019-03-14 23:55                                 ` James Bottomley
2019-03-13 15:01           ` overlayfs vs. fscrypt Eric Biggers
2019-03-13 15:01             ` Eric Biggers
2019-03-13 16:11             ` Al Viro
2019-03-13 16:33               ` Eric Biggers

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAJfpegsy31D+=VJ+By2a9TLCvZJwvAUpb+_bJ5JVTsmsbZJTKQ@mail.gmail.com' \
    --to=miklos@szeredi.hu \
    --cc=linux-fscrypt@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-unionfs@vger.kernel.org \
    --cc=richard@nod.at \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.