Smack: Handle io_uring kernel thread privileges

Smack: Handle io_uring kernel thread privileges

[ Upstream commit 942cb357ae7d9249088e3687ee6a00ed2745a0c7 ]

Smack assumes that kernel threads are privileged for smackfs
operations. This was necessary because the credential of the
kernel thread was not related to a user operation. With io_uring
the credential does reflect a user's rights and can be used.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>