Re: overlayfs vs. fscrypt - Richard Weinberger

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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 13:47:40 +0100	[thread overview]
Message-ID: <1852545.qrIQg0rEWx@blindfold> (raw)
In-Reply-To: <CAJfpegsy31D+=VJ+By2a9TLCvZJwvAUpb+_bJ5JVTsmsbZJTKQ@mail.gmail.com>

Am Mittwoch, 13. Mï¿½rz 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

As soon I load my key the real name is shown and I can read the file contents too.
That's why fscrypt has ->d_revalidate(). It checks for the key, if the key is
still not here -> stay with the old encrypted name. If the key is present
-> reveal the real name.

Same happens on the other direction if I unlink my key from the keyring.

> >
> > 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().

I hope my answer makes things more clear.

Thanks,
//richard

WARNING: multiple messages have this Message-ID (diff)

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 13:47:40 +0100	[thread overview]
Message-ID: <1852545.qrIQg0rEWx@blindfold> (raw)
In-Reply-To: <CAJfpegsy31D+=VJ+By2a9TLCvZJwvAUpb+_bJ5JVTsmsbZJTKQ@mail.gmail.com>

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

As soon I load my key the real name is shown and I can read the file contents too.
That's why fscrypt has ->d_revalidate(). It checks for the key, if the key is
still not here -> stay with the old encrypted name. If the key is present
-> reveal the real name.

Same happens on the other direction if I unlink my key from the keyring.

> >
> > 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().

I hope my answer makes things more clear.

Thanks,
//richard

next prev parent reply	other threads:[~2019-03-13 12:47 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
2019-03-13 12:47   ` Richard Weinberger [this message]
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

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