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

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-23 · updated 2026-10-19
• Weakness: CWE-362

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.

Affected products

• Linux kernel: from 4.11 before 5.15.212; from 5.16 before 6.1.178; from 6.2 before 6.6.145; from 6.7 before 6.12.96; from 6.13 before 6.18.39; from 6.19 before 7.1.4 — fixed in 5.15.212, 6.1.178, 6.12.96, 6.18.39, 6.6.145, 7.1.4

How to fix

Upgrade to a fixed version: Linux kernel 5.15.212, 6.1.178, 6.12.96, 6.18.39. Check the vendor advisory for mitigations.

References

• https://cdn2.qualys.com/advisory/2026/07/22/RefluXFS.txt
• https://git.kernel.org/stable/c/206c09b04dc5469c7ff14d8aceff2d47c88078d9
• https://git.kernel.org/stable/c/2f4acd0fcd862e22eab45690ec2c08c80b6ef2e7
• https://git.kernel.org/stable/c/44f891bc088958399eec27f7604928694aa35581
• https://git.kernel.org/stable/c/50f0012da1040f69a4e788cd9aed587c9a04983f
• https://git.kernel.org/stable/c/b8c9aa832b52680ee40d6cab0efb081f9a69df05
• https://git.kernel.org/stable/c/dc11be133efca5fe3a2fb02b016dee825cc12f18
• https://git.kernel.org/stable/c/e705d81a7193dd19e69b8e2bad4696d78a4ea075
• http://www.openwall.com/lists/oss-security/2026/07/22/14
• http://www.openwall.com/lists/oss-security/2026/07/22/18
• http://www.openwall.com/lists/oss-security/2026/07/22/19
• http://www.openwall.com/lists/oss-security/2026/07/31/3

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