GHSA-PXHV-6MJW-34J3
Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-23 15:31In 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.
{
"affected": [],
"aliases": [
"CVE-2026-98975"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-23T13:17:19Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: stop exchanging reflink flags when exchanging mappings\n\nWhen an exchange covers both files from offset 0 to i_disk_size,\nxmi_can_exchange_reflink_flags() assumes every mapping moved and hands\nthe reflink flag over to the other file.\n\nThat assumption is wrong. A file can still own shared blocks past\ni_disk_size, e.g. after EXCHANGE_RANGE_TO_EOF sets a smaller size\nwithout unmapping anything. The flag is cleared anyway, and the next\nwrite to such a block happens in place instead of CoW, corrupting the\nother file that shares it.\n\nCommit a23eca88448e (\"xfs: fix exchange-range reflink flag clearing\nissue with INO1_WRITTEN\") fixed one instance of this. Rather than add\nanother special case, stop moving the flags.\nxfs_exchmaps_ensure_reflink() already sets the flag on both inodes\nbefore the exchange, so both just keep it.\n\nNothing sets CLEAR_INO{1,2}_REFLINK anymore. Intents logged by older\nkernels may still carry them; recovery already masks them off, so they\nstay in the log format mask and are ignored.\n\nXFS_IOC_SWAPEXT has the same problem: it moves the reflink flag from\none inode to the other along with the extents. Just removing that is\nnot enough here: the exchange path flags both inodes up front in\nxfs_exchmaps_ensure_reflink(), but swapext has no such step, so the\ninode receiving the shared extents would be left without the flag.\nSet it on both inodes instead, and make sure both have a CoW fork,\nsince an inode with the reflink flag is expected to have one.\n\nThe flag now stays until FALLOC_FL_UNSHARE_RANGE, xfs_scrub, or a\ntruncate to zero removes it.",
"id": "GHSA-pxhv-6mjw-34j3",
"modified": "2026-10-23T15:31:33Z",
"published": "2026-10-23T15:31:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98975"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4756c94260e69ce42612b8220c3614f02f7a11d5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7d3b9b2c9dc57f93f36c716ab752548cb4db9900"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d84d6c1a7f1e2de9e601703a326a4c1b7b421943"
}
],
"schema_version": "1.4.0",
"severity": []
}
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