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From: Richard Weinberger <richard@nod.at>
To: Miklos Szeredi <miklos@szeredi.hu>
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 14:32:02 +0100	[thread overview]
Message-ID: <4066872.KGdO14EQMx@blindfold> (raw)
In-Reply-To: <CAJfpegtgfuAkgv26QH6Ht25OeMiev-QvEf7ror4KAbud7FADgg@mail.gmail.com>

Am Mittwoch, 13. März 2019, 14:24:47 CET schrieb Miklos Szeredi:
> > 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.
> 
> There's the underlying filesystem view where admin can delete files,
> etc.   And there's the fscrypt layer stacked on top of the underlying
> fs, which en/decrypts files *in case the user has the key*.  What if
> one user has a key, but the other one doesn't?  Will d_revalidate
> constantly switch the set of dentries between the encrypted filenames
> and the decrypted ones?  Sounds crazy.  And the fact that NTFS does
> this doesn't make it any less crazy...

Well, I didn't come up with this feature. :-)

If one user has the key and the other not, a classic multi-user
system, then you need to make sure that the affected fscrypt instances
are not visible by both.
For example by using mount namespaces to make sure that user a can only
see /home/foo and user b only /home/bar.
Or removing the search permission on /home/foo and /home/bar.

I know, I know, but that's how it is...
Maybe Ted or Eric can give more details on why they chose this approach.

Thanks,
//richard






  reply	other threads:[~2019-03-13 13:32 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-13 12:31 overlayfs vs. fscrypt Richard Weinberger
2019-03-13 12:36 ` Miklos Szeredi
2019-03-13 12:47   ` Richard Weinberger
2019-03-13 12:58     ` Miklos Szeredi
2019-03-13 13:00       ` Richard Weinberger
2019-03-13 13:24         ` Miklos Szeredi
2019-03-13 13:32           ` Richard Weinberger [this message]
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 15:36                 ` 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 20:33               ` Richard Weinberger
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                         ` [PATCH 1/4] fscrypt: Implement FS_CFLG_OWN_D_OPS Richard Weinberger
2019-03-14 17:15                         ` [PATCH 2/4] fscrypt: Export fscrypt_d_ops 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                         ` [PATCH 4/4] ubifs: Implement new mount option, fscrypt_key_required Richard Weinberger
2019-03-14 17:49                           ` Eric Biggers
2019-03-14 20:54                             ` Richard Weinberger
2019-03-14 23:07                               ` Theodore Ts'o
2019-03-15  7:48                                 ` Richard Weinberger
2019-03-15 13:51                                   ` Theodore Ts'o
2019-03-15 13:59                                     ` Richard Weinberger
2019-03-14 23:15                           ` James Bottomley
2019-03-14 23:42                             ` Theodore Ts'o
2019-03-14 23:55                               ` James Bottomley
2019-03-13 15:01           ` overlayfs vs. fscrypt Eric Biggers
2019-03-13 16:11             ` Al Viro
2019-03-13 16:33               ` Eric Biggers

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