UBUNTU-CVE-2026-98987: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: namespace: look at the topmost mount for a mount namespace file attachrecursivemnt() 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 CLCOPYMNTNSFILE 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 mntchangemountpoint() 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 movemount(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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.18~24.04.1 - Upgrade
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ubuntu/linux-azure-fde-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1019.19~24.04.1 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.19~24.04.1 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1016.18~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-43.43.1~24.04.2 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.3.0-10.10 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.3.0-1004.4 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.3.0-1004.4 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.3.0-1004.5 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.3.0-1004.4 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.3.0-1004.4 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 7.3.0-1004.4 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.3.0-10.10.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.3.0-10.10.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-43.43 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1017.18 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1020.21 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1019.19 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1017.19 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1010.11 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1018.18 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1018.18 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-43.43.1 - Compensating control
Update the mount-namespace attach logic so the mount-chain traversal examines every mount, including the topmost mount, before mnt_change_mountpoint() attaches the existing mount.
Event History
Frequently Asked Questions
Which Ubuntu systems are potentially affected?
Systems using the listed Ubuntu kernel packages may be affected: linux, linux-riscv, linux-realtime, linux-azure, linux-gcp, linux-azure-fde, linux-hwe-edge, and linux-gke. The provided data does not identify affected or fixed package versions.
What conditions are needed to trigger the issue?
The issue involves recursive mount attachment involving a mount namespace file. It occurs when the topmost mount in the source chain is the only mount namespace file, causing handling of propagated mount copies to use an unreachable nsfs dentry.
What is the operational impact if triggered?
A mount can become inaccessible because no path walk in the copied mount namespace reaches it. The replacement copy also cannot be synchronously unmounted while it has a child mount.