Bug 2535405 (CVE-2026-89965)

Summary: CVE-2026-89965 kernel: nvdimm/btt: reject an arena whose nfree is below the lane count
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's nvdimm/btt component. This vulnerability arises from insufficient validation of the `nfree` field in the BTT info block, which is read from the storage medium. A specially crafted or foreign arena with an `nfree` value below the expected lane count can cause an out-of-bounds write when accessing per-lane data structures. This could lead to memory corruption.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-09-16 12:44:00 UTC 
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.
Comment 1 Mauro Matteo Cascella 2026-09-17 09:26:52 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89965.mbox