Re: [RFC] Preliminary BTRFS Encryption

[Anand Jain <anand.jain@oracle.com>]

Thanks for comments.
Pls see inline as below.

On 09/15/2016 07:37 PM, Austin S. Hemmelgarn wrote:
> On 2016-09-13 09:39, Anand Jain wrote:
>>
>> This patchset adds btrfs encryption support.
>>
>> The main objective of this series is to have bugs fixed and stability.
>> I have verified with fstests to confirm that there is no regression.
>>
>> A design write-up is coming next, however here below is the quick example
>> on the cli usage. Please try out, let me know if I have missed something.
>>
>> Also would like to mention that a review from the security experts is
>> due,
>> which is important and I believe those review comments can be
>> accommodated
>> without major changes from here.
>>
>> Also yes, thanks for the emails, I hear, per file encryption and inline
>> with vfs layer is also important, which is wip among other things in the
>> list.
>>
>> As of now these patch set supports encryption on per subvolume, as
>> managing properties on per subvolume is a kind of core to btrfs, which is
>> easier for data center solution-ing, seamlessly persistent and easy to
>> manage.
>>
>>
>> Steps:
>> -----
>>
>> Make sure following kernel TFMs are compiled in.
>> # cat /proc/crypto | egrep 'cbc\(aes\)|ctr\(aes\)'
>> name         : ctr(aes)
>> name         : cbc(aes)
>>
>> Create encrypted subvolume.
>> # btrfs su create -e 'ctr(aes)' /btrfs/e1
>> Create subvolume '/btrfs/e1'
>> Passphrase:
>> Again passphrase:
>>
>> A key is created and its hash is updated into the subvolume item,
>> and then added to the system keyctl.
>> # btrfs su show /btrfs/e1 | egrep -i encrypt
>>     Encryption:         ctr(aes)@btrfs:75197c8e (594790215)
>>
>> # keyctl show 594790215
>> Keyring
>>  594790215 --alsw-v      0     0  logon: btrfs:75197c8e
>>
>>
>> Now any file data extents under the subvol /btrfs/e1 will be
>> encrypted.
>>
>> You may revoke key using keyctl or btrfs(8) as below.
>> # btrfs su encrypt -k out /btrfs/e1
>>
>> # btrfs su show /btrfs/e1 | egrep -i encrypt
>>     Encryption:         ctr(aes)@btrfs:75197c8e (Required key not
>> available)
>>
>> # keyctl show 594790215
>> Keyring
>> Unable to dump key: Key has been revoked
>>
>> As the key hash is updated, If you provide wrong passphrase in the next
>> key in, it won't add key to the system. So we have key verification
>> from the day1.
>>
>> # btrfs su encrypt -k in /btrfs/e1
>> Passphrase:
>> Again passphrase:
>> ERROR: failed to set attribute 'btrfs.encrypt' to
>> 'ctr(aes)@btrfs:75197c8e' : Key was rejected by service
>>
>> ERROR: key set failed: Key was rejected by service
>>
>> # btrfs su encrypt -k in /btrfs/e1
>> Passphrase:
>> Again passphrase:
>> key for '/btrfs/e1' has  logged in with keytag 'btrfs:75197c8e'
>>
>> Now if you revoke the key the read / write fails with key error.
>>
>> # md5sum /btrfs/e1/2k-test-file
>> 8c9fbc69125ebe84569a5c1ca088cb14  /btrfs/e1/2k-test-file
>>
>> # btrfs su encrypt -k out /btrfs/e1
>>
>> # md5sum /btrfs/e1/2k-test-file
>> md5sum: /btrfs/e1/2k-test-file: Key has been revoked
>>
>> # cp /tfs/1k-test-file /btrfs/e1/
>> cp: cannot create regular file ‘/btrfs/e1/1k-test-file’: Key has been
>> revoked
>>
>> Plain text memory scratches for security reason is pending. As there
>> are some
>> key revoke notification challenges to coincide with encryption context
>> switch,
>> which I do believe should be fixed in the due course, but is not a
>> roadblock
>> at this stage.
>>



> Before I make any other comments, I should state that I asbolutely agree
> with Alex Elsayed about the issues with using CBC or CTR mode, and not
> supporting AE or AEAD modes.

   Alex comments was quite detailed, I did reply to it.
   Looks like you missed my reply to Alex's comments ?

> How does this handle cloning of extents?  Can extents be cloned across
> subvolume boundaries when one of the subvolumes is encrypted?

  Yes only if both the subvol keys match.

> Can they
> be cloned within an encrypted subvolume?

  Yes. That's things as usual.

> What happens when you try to
> clone them in either case if it isn't supported?

  Gets -EOPNOTSUPP.

Thanks, Anand