On Fri, 2021-04-30 at 18:03 -0700, Patrick Donnelly wrote:
On Fri, Apr 30, 2021 at 8:04 AM Jeff Layton
<jlayton(a)redhat.com> wrote:
On Fri, 2021-04-30 at 07:45 -0700, Patrick Donnelly wrote:
On Fri, Apr 30, 2021 at 7:33 AM Jeff Layton
<jlayton(a)redhat.com> wrote:
> We specifically need this for directories and symlinks during pathwalks
> too. Eventually we may also want to encrypt certain data for other inode
> types as well (e.g. block/char devices). That's less critical though.
>
> The problem with fetching it after the inode is first instantiated is
> that we can end up recursing into a separate request while encoding a
> path. For instance, see this stack trace that Luis reported:
>
https://lore.kernel.org/ceph-devel/53d5bebb28c1e0cd354a336a56bf103d5e3a6344…
>
> While that implementation stored the context in an xattr, the problem
> isstill the same if you have to fetch the context in the middle of
> building a path. The best solution is just to always ensure it's
> available.
Got it. Splitting the struct makes sense then. The pin cap would be
suitable for the immutable encryption context (if truly
immutable?).Otherwise maybe the Axs cap?
Ok. In that case, then we probably need to put the context blob under
AUTH caps so we can ensure that it's consulted during the permission
checks for pathwalks. The size will need to live under FILE.
Now for the hard part...what do we name these fields?
fscrypt_context
fscrypt_size
...or maybe...
fscrypt_auth
fscrypt_file
Since they'll be vector blobs, we can version these too so that we can
add other fields later if the need arises (even for non-fscrypt stuff).
Maybe we could consider:
client_opaque_auth
client_opaque_file
An opaque blob makes sense but you'd want a sentinel indicating it's
an fscrypt blob. Don't think we'd be able to have two competing
use-cases but it'd be nice to have it generic enough for future
encryption libraries maybe.
I'm going with fscrypt_auth and fscrypt_file for now. We can rename them
later though if we want. What I'll probably do is just declare a
versioned format for these blobs. The MDS won't care about it, but the
clients can follow that convention.
I've made a bit of progress on this this week (fixing up the encoding
and decoding was a bit of a hassle, fwiw). These fields are associated
with the core inodes. The clients will use SETATTR calls to set them,
though they will also be updated with cap flushes, etc.
I need to be able to validate this feature in userland though and I
don't really want to roll dedicated functions for them. What I may do is
add new vxattrs (ceph.fscrypt_auth and ceph.fscrypt_file) and have those
expose these fields. Doing a setxattr on them will do a SETATTR under
the hood. The alternative is to declare new libcephfs routines for
fetching and setting these.
A client-side vxattr sounds good to me.
--
Patrick Donnelly, Ph.D.
He / Him / His
Principal Software Engineer
Red Hat Sunnyvale, CA
GPG: 19F28A586F808C2402351B93C3301A3E258DD79D