---
id: "CVE-2026-98446"
kind: "vulnerability"
aliases: ["CVE-2026-98446"]
title: "Linux kernel XFS: metadata reservation underflow corrupts free block count"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["kernel", "linux", "runtime", "xfs"]
not_affected_if: []
published_at: "2026-10-18T16:16:54+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:27:27+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98446", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel XFS: metadata reservation underflow corrupts free block count

In the XFS filesystem code, reserving space for a metadata btree file can underflow a counter when the reservation falls below the space that file already uses. The bad subtraction makes the kernel release a huge amount of free space it does not have, which can corrupt filesystem accounting.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98446

## From the sources

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

xfs: don't let hidden_space go negative in xfs_metafile_resv_init

LOLLM points out that if the amount of fdblocks that we can reserve for
a metadata btree file goes below the space already used by that file,
then the hidden_space subtraction can underflow, causing
xfs_dec_fdblocks to subtract a huge amount of space.  We never want the
target to be less than the used sapce, so fix the logic that adjusts
dblocks_avail downwards.

Also fix an error in the adjacent comment.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_