Re: [RFC PATCH v2 0/3] ceph: add support for snapshot names encryption

[Luís Henriques]

Xiubo Li <xiubli@xxxxxxxxxx> writes:

> On 3/17/22 6:01 PM, Jeff Layton wrote:
>> I'm not sure we want to worry about .snap directories here since they
>> aren't "real". IIRC, snaps are inherited from parents too, so you could
>> do something like
>>
>>      mkdir dir1
>>      mkdir dir1/.snap/snap1
>>      mkdir dir1/dir2
>>      fscrypt encrypt dir1/dir2
>>
>> There should be nothing to prevent encrypting dir2, but I'm pretty sure
>> dir2/.snap will not be empty at that point.
>
> If we don't take care of this. Then we don't know which snapshots should do
> encrypt/dencrypt and which shouldn't when building the path in lookup and when
> reading the snapdir ?

In my patchset (which I plan to send a new revision later today, I think I
still need to rebase it) this is handled by using the *real* snapshot
parent inode.  If we're decrypting/encrypting a name for a snapshot that
starts with a '_' character, we first find the parent inode for that
snapshot and only do the operation if that parent is encrypted.

In the other email I suggested that we could prevent enabling encryption
in a directory when there are snapshots above in the hierarchy.  But now
that I think more about it, it won't solve any problem because you could
create those snapshots later and then you would still need to handle these
(non-encrypted) "_name_xxxx" snapshots anyway.

Cheers,
-- 
Luís

>
> -- Xiubo
>
>>
>> -- Jeff
>>
>> On Thu, 2022-03-17 at 13:27 +0800, Xiubo Li wrote:
>>> Hi Luis,
>>>
>>> There has another issue you need to handle at the same time.
>>>
>>> Currently only the empty directory could be enabled the file encryption,
>>> such as for the following command:
>>>
>>> $ fscrypt encrypt mydir/
>>>
>>> But should we also make sure that the mydir/.snap/ is empty ?
>>>
>>> Here the 'empty' is not totally empty, which allows it should allow long
>>> snap names exist.
>>>
>>> Make sense ?
>>>
>>> - Xiubo
>>>
>>>
>>> On 3/16/22 12:19 AM, Luís Henriques wrote:
>>>> Hi!
>>>>
>>>> A couple of changes since v1:
>>>>
>>>> - Dropped the dentry->d_flags change in ceph_mkdir().  Thanks to Xiubo
>>>>     suggestion, patch 0001 now skips calling ceph_fscrypt_prepare_context()
>>>>     if we're handling a snapshot.
>>>>
>>>> - Added error handling to ceph_get_snapdir() in patch 0001 (Jeff had
>>>>     already pointed that out but I forgot to include that change in previous
>>>>     revision).
>>>>
>>>> - Rebased patch 0002 to the latest wip-fscrypt branch.
>>>>
>>>> - Added some documentation regarding snapshots naming restrictions.
>>>>
>>>> As before, in order to test this code the following PRs are required:
>>>>
>>>>     mds: add protection from clients without fscrypt support #45073
>>>>     mds: use the whole string as the snapshot long name #45192
>>>>     mds: support alternate names for snapshots #45224
>>>>     mds: limit the snapshot names to 240 characters #45312
>>>>
>>>> Luís Henriques (3):
>>>>     ceph: add support for encrypted snapshot names
>>>>     ceph: add support for handling encrypted snapshot names
>>>>     ceph: update documentation regarding snapshot naming limitations
>>>>
>>>>    Documentation/filesystems/ceph.rst |  10 ++
>>>>    fs/ceph/crypto.c                   | 158 +++++++++++++++++++++++++----
>>>>    fs/ceph/crypto.h                   |  11 +-
>>>>    fs/ceph/inode.c                    |  31 +++++-
>>>>    4 files changed, 182 insertions(+), 28 deletions(-)
>>>>
>