CVE-2026-89965

/// Technical description

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

nvdimm/btt: reject an arena whose nfree is below the lane count

The BTT info block's nfree field, the number of reserve free blocks, is

read from the medium without validation. btt_freelist_init() and

btt_rtt_init() size the per-lane freelist[] and rtt[] arrays by nfree,

but the I/O path indexes them by the lane from nd_region_acquire_lane(),

which is bounded by nd_region->num_lanes (ND_MAX_LANES), not by nfree.

A crafted or foreign arena whose nfree is below the lane count makes

freelist[lane]/rtt[lane] run past the allocation: an out-of-bounds write.

btt.rst documents the nlanes = min(nfree, num_cpus) invariant, which the

code does not currently honor: num_lanes is ND_MAX_LANES regardless of

nfree. Reject an arena whose nfree is below num_lanes at discovery,

before the per-lane arrays are allocated, enforcing that invariant.

/// 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