CVE-2023-53680

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

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

OPDESC() simply indexes into nfsd4_ops[] 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 opnum value.

nfsd4_decode_compound() is not so careful, and can invoke OPDESC() with opnum set to OP_ILLEGAL, which is 10044 -- well beyond the end of nfsd4_ops[].

NFSD could call OPDESC() with opnum == OP_ILLEGAL, indexing past nfsd4_ops[] and causing an out-of-bounds read leading to a crash. A remote unauthenticated NFSv4 client could trigger this via a crafted COMPOUND, impacting availability of the NFS server. The fix sets op->opdesc = NULL, assigns opdesc only when opnum is in range, and removes the unconditional OPDESC() call.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent module nfs from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.