xfs: delete attr leaf freemap entries when empty_CVE-2026-43187

8.8 / 10

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Description

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 it's 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 isn't in and of
itself a problem because the code in _leaf_add that finds free space
ignores any freemap entry with zero size.

However, there's 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
that's 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.

AI Analysis

AI processing failed - invalid JSON response

Basic Information

ID CVE-2026-43187

Source Linux

Published May 6, 2026 at 11:27

Modified May 8, 2026 at 12:41

Affected Product

Vendor Linux

Product Linux

Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2

Affected Versions Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Linux Linux 2.6.12

References

{
    "lastseen": "",
    "description": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: delete attr leaf freemap entries when empty\n\nBack in commit 2a2b5932db6758 (\"xfs: fix attr leaf header freemap.size\nunderflow\"), Brian Foster observed that it's possible for a small\nfreemap at the end of the end of the xattr entries array to experience\na size underflow when subtracting the space consumed by an expansion of\nthe entries array.  There are only three freemap entries, which means\nthat it is not a complete index of all free space in the leaf block.\n\nThis code can leave behind a zero-length freemap entry with a nonzero\nbase.  Subsequent setxattr operations can increase the base up to the\npoint that it overlaps with another freemap entry.  This isn't in and of\nitself a problem because the code in _leaf_add that finds free space\nignores any freemap entry with zero size.\n\nHowever, there's another bug in the freemap update code in _leaf_add,\nwhich is that it fails to update a freemap entry that begins midway\nthrough the xattr entry that was just appended to the array.  That can\nresult in the freemap containing two entries with the same base but\ndifferent sizes (0 for the \"pushed-up\" entry, nonzero for the entry\nthat's actually tracking free space).  A subsequent _leaf_add can then\nallocate xattr namevalue entries on top of the entries array, leading to\ndata loss.  But fixing that is for later.\n\nFor now, eliminate the possibility of confusion by zeroing out the base\nof any freemap entry that has zero size.  Because the freemap is not\nintended to be a complete index of free space, a subsequent failure to\nfind any free space for a new xattr will trigger block compaction, which\nregenerates the freemap.\n\nIt looks like this bug has been in the codebase for quite a long time.",
    "published": "2026-05-06T11:27:57.727Z",
    "modified": "2026-05-08T12:41:05.734Z",
    "type": "cve",
    "title": "xfs: delete attr leaf freemap entries when empty",
    "source": "Linux",
    "references": "https://git.kernel.org/stable/c/f3c0d1fc1eadbb4adbee5ab7757d41d35f48325b\nhttps://git.kernel.org/stable/c/aa9083d97e2157da3c6fb45ddb1a97af7f188f7f\nhttps://git.kernel.org/stable/c/a631899025d47ea1aa6464d76db5b4d3b6d196fd\nhttps://git.kernel.org/stable/c/ffaf5c99d0f862db021fb1af8b813c1416b1beb2\nhttps://git.kernel.org/stable/c/e1b8c6452ee99a30e188a88f3f3f804fb1c6004a\nhttps://git.kernel.org/stable/c/f31a8334e1c54b126fcecf98645a49b6bc5ad399\nhttps://git.kernel.org/stable/c/479b05fc3ee272090f671b06a41f3da8aa78eece\nhttps://git.kernel.org/stable/c/6f13c1d2a6271c2e73226864a0e83de2770b6f34",
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