libceph: do not hard code max auth ticket len

We hard code cephx auth ticket buffer size to 256 bytes.  This isn't
enough for any moderate setups and, in case tickets themselves are not
encrypted, leads to buffer overflows (ceph_x_decrypt() errors out, but
ceph_decode_copy() doesn't - it's just a memcpy() wrapper).  Since the
buffer is allocated dynamically anyway, allocated it a bit later, at
the point where we know how much is going to be needed.

Fixes: http://tracker.ceph.com/issues/8979

Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@redhat.com>
static void ceph_x_destroy(struct ceph_auth_client *ac)
{
	struct ceph_x_info *xi = ac->private;
	struct rb_node *p;

	dout("ceph_x_destroy %p\n", ac);
	ceph_crypto_key_destroy(&xi->secret);

	while ((p = rb_first(&xi->ticket_handlers)) != NULL) {
		struct ceph_x_ticket_handler *th =
			rb_entry(p, struct ceph_x_ticket_handler, node);
		remove_ticket_handler(ac, th);
	}

	if (xi->auth_authorizer.buf)
		ceph_buffer_put(xi->auth_authorizer.buf);

	kfree(ac->private);
	ac->private = NULL;
}

static void ceph_x_destroy(struct ceph_auth_client *ac)
{
	struct ceph_x_info *xi = ac->private;
	struct rb_node *p;

	dout("ceph_x_destroy %p\n", ac);
	ceph_crypto_key_destroy(&xi->secret);

	while ((p = rb_first(&xi->ticket_handlers)) != NULL) {
		struct ceph_x_ticket_handler *th =
			rb_entry(p, struct ceph_x_ticket_handler, node);
		remove_ticket_handler(ac, th);
	}

	if (xi->auth_authorizer.buf)
		ceph_buffer_put(xi->auth_authorizer.buf);

	kfree(ac->private);
	ac->private = NULL;
}
