CVE-2026-89965

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.

References

• https://git.kernel.org/stable/c/59d5cd1f42b4bab3609512c3cb3d3540d3d21da7
• https://git.kernel.org/stable/c/6a1f2e5ed9267ca19187038ac635393c165213ac
• https://git.kernel.org/stable/c/6b1faf1f099f7060b5f1f2f0d024132581f1726e
• https://git.kernel.org/stable/c/6f79d1a5f2611a3d36e9312be5425cd9cb397c51
• https://git.kernel.org/stable/c/9dfa11cef4750b67591307f2c62e47a23d60e4b7