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From:   =?utf-8?Q?Lu=C3=ADs_Henriques?= <lhenriques@suse.de>
To:     Jeff Layton <jlayton@kernel.org>
Cc:     Xiubo Li <xiubli@redhat.com>, Ilya Dryomov <idryomov@gmail.com>,
        Ceph Development <ceph-devel@vger.kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 0/3] ceph: add support for snapshot names encryption
References: <20220315161959.19453-1-lhenriques@suse.de>
        <5b53e812-d49b-45f0-1219-3dbc96febbc1@redhat.com>
        <329abedd9d9938de95bf4f5600acdcd6a846e6be.camel@kernel.org>
        <3c8b78c4-5392-b81c-e76f-64fcce4f3c0f@redhat.com>
        <87wngshlzb.fsf@brahms.olymp>
        <c2f494b61674e63985e4e2a0fb3b6c503e17334b.camel@kernel.org>
Date:   Thu, 17 Mar 2022 15:59:02 +0000
In-Reply-To: <c2f494b61674e63985e4e2a0fb3b6c503e17334b.camel@kernel.org> (Jeff
        Layton's message of "Thu, 17 Mar 2022 08:01:17 -0400")
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Jeff Layton <jlayton@kernel.org> writes:

> On Thu, 2022-03-17 at 11:11 +0000, Lu=C3=ADs Henriques wrote:
>> Xiubo Li <xiubli@redhat.com> writes:
>>=20
>> > 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 co=
uld
>> > > do something like
>> > >=20
>> > >      mkdir dir1
>> > >      mkdir dir1/.snap/snap1
>> > >      mkdir dir1/dir2
>> > >      fscrypt encrypt dir1/dir2
>> > >=20
>> > > There should be nothing to prevent encrypting dir2, but I'm pretty s=
ure
>> > > dir2/.snap will not be empty at that point.
>> >=20
>> > If we don't take care of this. Then we don't know which snapshots shou=
ld do
>> > encrypt/dencrypt and which shouldn't when building the path in lookup =
and when
>> > reading the snapdir ?
>>=20
>> 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.
>>=20
>> 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 the=
se
>> (non-encrypted) "_name_xxxx" snapshots anyway.
>>=20
>
> Yeah, that sounds about right.
>
> What happens if you don't have the snapshot parent's inode in cache?
> That can happen if you (e.g.) are running NFS over ceph, or if you get
> crafty with name_to_handle_at() and open_by_handle_at().
>
> Do we have to do a LOOKUPINO in that case or does the trace contain that
> info? If it doesn't then that could really suck in a big hierarchy if
> there are a lot of different snapshot parent inodes to hunt down.
>
> I think this is a case where the client just doesn't have complete
> control over the dentry name. It may be better to just not encrypt them
> if it's too ugly.

I *think* this is covered by my last revision.  I didn't really tested
NFS, but this was why the patches are using ceph_get_inode() and falling
back to ceph_find_inode().  I tested this by directly mounting an
encrypted directory that had snapshots from a realm that wasn't in the
mount root.

(Obviously, these snapshot names are *not* encrypted because they belong
to snapshots that are not encrypted either.)

Cheers,
--=20
Lu=C3=ADs

> Another idea might be to just use the same parent inode (maybe the
> root?) for all snapshot names. It's not as secure, but it's probably
> better than nothing.
> --=20
> Jeff Layton <jlayton@kernel.org>