CVE-2026-46024: libceph: Prevent potential null-ptr-deref in ceph_handle_auth_reply()

In the Linux kernel, the following vulnerability has been resolved:

libceph: Prevent potential null-ptr-deref in cephhandleauthreply()

If a message of type CEPHMSGAUTHREPLY contains a zero value for both protocol and result, this is currently not treated as an error. In case of ac->negotiating == true and ac->protocol > 0, this leads to setting ac->protocol = 0 and ac->ops = NULL. Thereafter, the check for ac->protocol != protocol returns false, and initprotocol() is not called. Subsequently, ac->ops->handlereply() is called, which leads to a null pointer dereference, because ac->ops is still NULL.

This patch changes the check for ac->protocol != protocol to !ac->protocol, as this also includes the case when the protocol was set to zero in the message. This causes the message to be treated as containing a bad auth protocol.