CVE-2026-43187

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

xfs: delete attr leaf freemap entries when empty

Back in commit 2a2b5932db6758 (xfs: fix attr leaf header freemap.size underflow), Brian Foster observed that its possible for a small freemap at the end of the end of the xattr entries array to experience a size underflow when subtracting the space consumed by an expansion of the entries array. There are only three freemap entries, which means that it is not a complete index of all free space in the leaf block.

This code can leave behind a zero-length freemap entry with a nonzero base. Subsequent setxattr operations can increase the base up to the point that it overlaps with another freemap entry. This isnt in and of itself a problem because the code in _leaf_add that finds free space ignores any freemap entry with zero size.

However, theres another bug in the freemap update code in _leaf_add, which is that it fails to update a freemap entry that begins midway through the xattr entry that was just appended to the array. That can result in the freemap containing two entries with the same base but different sizes (0 for the pushed-up entry, nonzero for the entry thats actually tracking free space). A subsequent _leaf_add can then allocate xattr namevalue entries on top of the entries array, leading to data loss. But fixing that is for later.

For now, eliminate the possibility of confusion by zeroing out the base of any freemap entry that has zero size. Because the freemap is not intended to be a complete index of free space, a subsequent failure to find any free space for a new xattr will trigger block compaction, which regenerates the freemap.

It looks like this bug has been in the codebase for quite a long time.

Weakness

The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

Affected Software

References

• https://git.kernel.org/stable/c/479b05fc3ee272090f671b06a41f3da8aa78eece
• https://git.kernel.org/stable/c/6f13c1d2a6271c2e73226864a0e83de2770b6f34
• https://git.kernel.org/stable/c/a631899025d47ea1aa6464d76db5b4d3b6d196fd
• https://git.kernel.org/stable/c/aa9083d97e2157da3c6fb45ddb1a97af7f188f7f
• https://git.kernel.org/stable/c/e1b8c6452ee99a30e188a88f3f3f804fb1c6004a
• https://git.kernel.org/stable/c/f31a8334e1c54b126fcecf98645a49b6bc5ad399
• https://git.kernel.org/stable/c/f3c0d1fc1eadbb4adbee5ab7757d41d35f48325b
• https://git.kernel.org/stable/c/ffaf5c99d0f862db021fb1af8b813c1416b1beb2