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.
--
Patrick Donnelly, Ph.D.
He / Him / His
Principal Software Engineer
Red Hat Sunnyvale, CA
GPG: 19F28A586F808C2402351B93C3301A3E258DD79D