CVE-2023-53680 NFSD: Avoid calling OPDESC() with ops->opnum == OP_ILLEGAL

In the Linux kernel, the following vulnerability has been resolved: NFSD: Avoid calling OPDESC with ops-opnum == OPILLEGAL OPDESC simply indexes into nfsd4ops by the op's operation number, without range checking that value. It assumes callers are careful to avoid calling it with an out-of-bounds...