CVE-2026-89656

/// Technical description

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

libceph: reject buckets with mismatched CRUSH ids

crush_decode() stores bucket data by array slot, and the mapper later

derives the per-bucket workspace index from the decoded bucket id. A

malformed map can therefore make one bucket reuse another bucket's

workspace by encoding an id different from -1 - slot.

For uniform buckets, the second replica selection expands the source

bucket's permutation into that aliased workspace buffer. If the source

bucket is larger than the aliased bucket, the write runs past the smaller

permutation array and can escape the kvmalloc'd CRUSH workspace. KASAN

reports a slab OOB write of 4 bytes in bucket_perm_choose().

Reject buckets whose encoded id does not match their array slot. Valid

CRUSH maps already use the canonical negative id corresponding to the

bucket slot, so this restores the invariant expected by

work->work[-1 - in->id] without changing valid map behavior.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References