CVE-2026-98987 (GCVE-0-2026-98987)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:20 – Updated: 2026-10-23 12:20
VLAI
Title
namespace: look at the topmost mount for a mount namespace file
Summary
In the Linux kernel, the following vulnerability has been resolved: namespace: look at the topmost mount for a mount namespace file attach_recursive_mnt() preallocates a mountpoint for the root of the topmost mount of the source so that a mount that already sits at the destination can be put on top of the source or on top of one of its propagated copies. The copies are made without CL_COPY_MNT_NS_FILE so their chain of overmounts is shorter than the source's. It ends below the first bind mount of a mount namespace file. So while the loop walks up the chain of the source it remembers the mountpoint of that mount in "shorter" and the existing mount is put there for the copies. But the loop ends at the topmost mount without ever looking at it. If the topmost mount is the only mount namespace file in the chain "shorter" stays NULL and mnt_change_mountpoint() attaches the existing mount of the copy below the root of the mount namespace file. That's a dentry of nsfs. No path walk in the copy's mount namespace ever gets there. The mount is gone until its parent goes and the copy that took its place can't be unmounted synchronously because it has a child: S bind mount of a file N bind mount of a mount namespace file on top of S A shared mount, B a slave of A, Q mounted on B/file move_mount(S, A/file) cat B/file -> the content of S instead of Q umount B/file -> EBUSY Look at every mount of the chain including the topmost one.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6643 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 , < b9c40553f6ceba50042281eef6f701e5fb719726 (git)
Affected: 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 , < 87ecd4c6da146363384a603bd9e90c90e7275536 (git)
Affected: 96f5d2e051653f2cfe9137c5d3c7794c358ffb03 , < 8714b44adac7b10506e1db3ef1710689751f0f10 (git)
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Linux Linux Affected: 6.17
Unaffected: 0 , < 6.17 (semver)
Unaffected: 6.18.57 , ≤ 6.18.* (semver)
Unaffected: 7.2.11 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: look at the topmost mount for a mount namespace file\n\nattach_recursive_mnt() preallocates a mountpoint for the root of the\ntopmost mount of the source so that a mount that already sits at the\ndestination can be put on top of the source or on top of one of its\npropagated copies.\n\nThe copies are made without CL_COPY_MNT_NS_FILE so their chain of\novermounts is shorter than the source\u0027s. It ends below the first bind\nmount of a mount namespace file. So while the loop walks up the chain of\nthe source it remembers the mountpoint of that mount in \"shorter\" and\nthe existing mount is put there for the copies.\n\nBut the loop ends at the topmost mount without ever looking at it. If\nthe topmost mount is the only mount namespace file in the chain\n\"shorter\" stays NULL and mnt_change_mountpoint() attaches the existing\nmount of the copy below the root of the mount namespace file. That\u0027s a\ndentry of nsfs. No path walk in the copy\u0027s mount namespace ever gets\nthere. The mount is gone until its parent goes and the copy that took\nits place can\u0027t be unmounted synchronously because it has a child:\n\n  S      bind mount of a file\n  N      bind mount of a mount namespace file on top of S\n  A      shared mount, B a slave of A, Q mounted on B/file\n\n  move_mount(S, A/file)\n  cat B/file          -\u003e the content of S instead of Q\n  umount B/file       -\u003e EBUSY\n\nLook at every mount of the chain including the topmost one."
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}



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