CVE-2026-89965
HighCVSS 7.8Summary
In the Linux kernel, the nfree field in the BTT info block is read from the medium without validation. btt_freelist_init() and btt_rtt_init() size the freelist[] and rtt[] arrays by nfree, but the I/O path indexes them by the lane bounded by num_lanes rather than nfree. An arena with nfree below the lane count causes an out-of-bounds write.
Risk Assessment
This can lead to kernel memory corruption and system panic when mounting a crafted or foreign NVDIMM BTT medium. It requires physical access to the medium or the ability to swap it.
Recommendation
Update the Linux kernel to a version containing the fix that rejects an arena whose nfree is below num_lanes at discovery. Avoid mounting untrusted NVDIMM media.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS