---
id: "CVE-2026-98907"
kind: "vulnerability"
aliases: ["CVE-2026-98907"]
title: "Linux kernel btrfs: race when reading superblock during block size change"
severity: "unknown"
cvss: null
epss: 0.00215
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["btrfs", "infrastructure", "linux-kernel", "self-hosted"]
not_affected_if: ["no-btrfs"]
published_at: "2026-10-23T12:18:24+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98907", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-98907", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux kernel btrfs: race when reading superblock during block size change

A race in the Linux kernel's btrfs code lets the superblock read in sb_write_pointer() run while the block device's block size is being changed. The sources do not state what an attacker gains from this race.

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

## How to check

- Run `uname -r` to see the running kernel version and compare it against the fixed kernel listed in the NVD record.
- Check whether btrfs is in use with `lsblk -f` or `findmnt -t btrfs`.

## Fix

- Install the kernel release that contains the upstream btrfs fix (commit subject: 'btrfs: protect sb_write_pointer() with invalidate lock'); the fixed version is unknown from these sources.
- Reboot into the patched kernel.

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98907
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-98907

## From the sources

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

btrfs: protect sb_write_pointer() with invalidate lock

sb_write_pointer() reads the super block from the block device page cache
using read_cache_page_gfp(). This has the same race with BLKBSZSET as the
one fixed by commit 3f29d661e568 ("btrfs: sync read disk super and set
block size").

Take the mapping invalidate lock around read_cache_page_gfp() to
serialize the read against block size changes.

---

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