namespace: keep the lock on a mount that a propagated copy is moved beneath

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Summary

CVECVE-2026-98976
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-23 13:17:19 UTC
Updated2026-10-23 13:17:19 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: namespace: keep the lock on a mount that a propagated copy is moved beneath attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the owner of a user namespace to replace its locked /proc or its root. The mount beneath takes on the job of covering the underlying mountpoint allowing the top mount to be unmounted. Consider two mount namespaces: (H) The host H has a shared mount P with a secret in P/d (Z) Z is a user namespace made from M. Its copy of P receives propagation from the host's P and its copy of M's cover on P/d is locked Z's owner must not get to see P/d. Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands beneath (Z)'s locked cover. The locked property is transfered from (Z)'s cover to the copy of X propagated beneath it. The cover is now unlocked. Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the covering mount is left unlocked on top of P/d. (Z) can now unmount it: Z: umount2(P/d) = EINVAL /* the cover is locked */ H: mount X on P/d, umount X /* both propagate into Z /* Z: umount2(P/d) = 0 /* the cover is now unlocked */ Z: read P/d/secret = "covered-by-root" /* secret revealed */ So only transfer the locked property to the mount beneath for mounts the caller has placed. A propagated copy that lands beneath a locked mount is locked as well so that the mount at the bottom of the stack carries a lock the way every check expects. The mount on top of it remains locked to ensure that it keeps covering even if the propagated mount is unmounted again.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected c62a4766937edec2962d52e583276b459b739f2d f1f0c24ca701d7d3061c7f69f7450f1734c11745 git Not specified
CNA Linux Linux affected c62a4766937edec2962d52e583276b459b739f2d d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4 git Not specified
CNA Linux Linux affected 7.1 Not specified
CNA Linux Linux unaffected 7.1 semver Not specified
CNA Linux Linux unaffected 7.2.11 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f1f0c24ca701d7d3061c7f69f7450f1734c11745 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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