CVE-2026-68158: libceph: Fix multiplication overflow in decode_new_up_state_weight()

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

libceph: Fix multiplication overflow in decodenewupstateweight()

If a message of type CEPHMSGOSDMAP contains a (maliciously) corrupted osdmap, out-of-bounds memory accesses may occur in decodenewupstateweight(). This happens because the bounds check for the newstate part is based on calculating its length depending on a len value read from the incoming message. This calculation may overflow leading to an incorrect bounds check. Subsequently, out-of-bounds reads may occur when decoding this part.

This patch switches the multiplication to use checkmuloverflow() to abort processing the osdmap if an overflow occurred. Therefore, osdmaps/messages containing large values for len that result in a multiplication overflow are treated as invalid.

[ idryomov: rename newstatelen -> newstateitemsize, formatting ]