btrfs: fix extent map leak in NOCOW direct I/O write (CVE-2026-89644) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-89644

btrfs: fix extent map leak in NOCOW direct I/O write

Answer in brief

CVE-2026-89644 records a Unknown severity vulnerability in btrfs: fix extent map leak in NOCOW direct I/O write. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 11, 2026Updated Sep 11, 2026Source checked Sep 11, 2026First seen by HOL Sep 11, 2026Material review Sep 11, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af <f42efd634c0ae7ba0ce2fc5e30e291b0803b0ae2 \|\| >=5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af <05a1a816eef8b3e4332620a64fc8cf45c4eb5c0d \|\| >=5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af <3f950867c307c5413d628a153ac44915bd117ffd	f42efd634c0ae7ba0ce2fc5e30e291b0803b0ae2, 05a1a816eef8b3e4332620a64fc8cf45c4eb5c0d, 3f950867c307c5413d628a153ac44915bd117ffd
Linux/Linuxgeneric	4.7	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to f42efd634c0ae7ba0ce2fc5e30e291b0803b0ae2 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 11, 2026

Sources and claim methodology

Upstream source description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix extent map leak in NOCOW direct I/O write btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an extent map reference that must be dropped on all exit paths. For direct writes into a NOCOW range, btrfs_get_blocks_direct_write() keeps using that extent map and asks btrfs_create_dio_extent() to allocate the ordered extent. If that fails, for example because btrfs_alloc_ordered_extent() fails, the function returns the error without dropping the input extent map. The PREALLOC path avoided this by dropping the input extent map before replacing it with the newly created one. Check the error from btrfs_create_dio_extent() before replacing the map and drop the input extent map on failure.

Quoted source text, attributed separately from HOL analysis.