CVE-2026-98977 (GCVE-0-2026-98977)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:19 – Updated: 2026-10-23 12:19
VLAI
Title
namespace: handle mount locking for automounts correctly
Summary
In the Linux kernel, the following vulnerability has been resolved: namespace: handle mount locking for automounts correctly If mounts are propagated across user namespaces, attach_recursive_mnt() locks every copy of the source mount to protect overmounts from vanishing and revealing the underlying files or directories. The user namespace is taken from the caller's mount namespaces since this is where the mounts end up. Except, that's not always true. Automounts may legitimately get popped in by tasks located in a different mount and user namespace during path lookup. Then check doesn't make sense at that point. The copy in the namespace of the parent - which may be the host's - is now locked and the host cannot change the flags of its own mounts anymore. Here's the reproducer: - host has debugfs mounted nosuid,nodev,noexec and shared - tracefs automount below it is not yet active - hand a child process a directory descriptor on that mount - child process enters auser and mount namespace - child process' namespace now holds a locked copy of the host's debugfs mount that receives propagation from it - child process stats "tracing/." through the descriptor - lookup runs on the host's mount so the automount lands below the host's mount - propagation puts a copy below the child's copy - both try to clear the flags on the mount they got, with a bind remount: host, on its own automount: MS_REMOUNT|MS_BIND = EPERM child, on the copy in its namespace: MS_REMOUNT|MS_BIND = 0 So the lock landed on the host's mount instead of the child's copy. Congrats. So we need to compare with the owner of the namespace the mount actually gets mounted on. For all regular cases that is the caller's mount namespace and so nothing changes. Detached trees in anonymous mount namespaces by be handed over via SCM_RIGHTS or inherited in other ways on purpose so the attaching task's mount namespace is authoritative, not the creator of the detached tree.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7061 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 , < 5e8f3ac8fa3d411b422ad32b9168c46a4824cc79 (git)
Affected: 132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 , < b3ccde78f1608836e62320428abc0e8aa9cf2329 (git)
Affected: 132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 , < e01c79761c7b3373e80094c5eadb21cb864fa8bc (git)
Affected: 132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 , < 6ab37fae14196ba2262b152a7d9222c50356d278 (git)
Affected: 132c94e31b8bca8ea921f9f96a57d684fa4ae0a9 , < 33aadc7c72055fca93cb5a3691d836ebf8b31c9b (git)
Affected: 9c773201d61272db49f8f33a83a3cb2a3fe4b14f (git)
Affected: 3.8.6 , < 3.9 (semver)
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Linux Linux Affected: 3.9
Unaffected: 0 , < 3.9 (semver)
Unaffected: 6.6.160 , ≤ 6.6.* (semver)
Unaffected: 6.12.114 , ≤ 6.12.* (semver)
Unaffected: 6.18.57 , ≤ 6.18.* (semver)
Unaffected: 7.2.11 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: handle mount locking for automounts correctly\n\nIf mounts are propagated across user namespaces, attach_recursive_mnt()\nlocks every copy of the source mount to protect overmounts from\nvanishing and revealing the underlying files or directories.\n\nThe user namespace is taken from the caller\u0027s mount namespaces since\nthis is where the mounts end up. Except, that\u0027s not always true.\nAutomounts may legitimately get popped in by tasks located in a\ndifferent mount and user namespace during path lookup.\n\nThen check doesn\u0027t make sense at that point. The copy in the namespace\nof the parent - which may be the host\u0027s - is now locked and the host\ncannot change the flags of its own mounts anymore.\n\nHere\u0027s the reproducer:\n\n- host has debugfs mounted nosuid,nodev,noexec and shared\n- tracefs automount below it is not yet active\n- hand a child process a directory descriptor on that mount\n- child process enters auser and mount namespace\n- child process\u0027 namespace now holds a locked copy of the host\u0027s debugfs\n  mount that receives propagation from it\n- child process stats \"tracing/.\" through the descriptor\n- lookup runs on the host\u0027s mount so the automount lands below the host\u0027s mount\n- propagation puts a copy below the child\u0027s copy\n- both try to clear the flags on the mount they got, with a bind remount:\n\n    host, on its own automount:            MS_REMOUNT|MS_BIND = EPERM\n    child, on the copy in its namespace:   MS_REMOUNT|MS_BIND = 0\n\nSo the lock landed on the host\u0027s mount instead of the child\u0027s copy.\nCongrats. So we need to compare with the owner of the namespace the\nmount actually gets mounted on. For all regular cases that is the\ncaller\u0027s mount namespace and so nothing changes.\n\nDetached trees in anonymous mount namespaces by be handed over via\nSCM_RIGHTS or inherited in other ways on purpose so the attaching task\u0027s\nmount namespace is authoritative, not the creator of the detached tree."
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: handle mount locking for automounts correctly\n\nIf mounts are propagated across user namespaces, attach_recursive_mnt()\nlocks every copy of the source mount to protect overmounts from\nvanishing and revealing the underlying files or directories.\n\nThe user namespace is taken from the caller\u0027s mount namespaces since\nthis is where the mounts end up. Except, that\u0027s not always true.\nAutomounts may legitimately get popped in by tasks located in a\ndifferent mount and user namespace during path lookup.\n\nThen check doesn\u0027t make sense at that point. The copy in the namespace\nof the parent - which may be the host\u0027s - is now locked and the host\ncannot change the flags of its own mounts anymore.\n\nHere\u0027s the reproducer:\n\n- host has debugfs mounted nosuid,nodev,noexec and shared\n- tracefs automount below it is not yet active\n- hand a child process a directory descriptor on that mount\n- child process enters auser and mount namespace\n- child process\u0027 namespace now holds a locked copy of the host\u0027s debugfs\n  mount that receives propagation from it\n- child process stats \"tracing/.\" through the descriptor\n- lookup runs on the host\u0027s mount so the automount lands below the host\u0027s mount\n- propagation puts a copy below the child\u0027s copy\n- both try to clear the flags on the mount they got, with a bind remount:\n\n    host, on its own automount:            MS_REMOUNT|MS_BIND = EPERM\n    child, on the copy in its namespace:   MS_REMOUNT|MS_BIND = 0\n\nSo the lock landed on the host\u0027s mount instead of the child\u0027s copy.\nCongrats. So we need to compare with the owner of the namespace the\nmount actually gets mounted on. For all regular cases that is the\ncaller\u0027s mount namespace and so nothing changes.\n\nDetached trees in anonymous mount namespaces by be handed over via\nSCM_RIGHTS or inherited in other ways on purpose so the attaching task\u0027s\nmount namespace is authoritative, not the creator of the detached tree."
          }
        ],
        "id": "CVE-2026-98977",
        "lastModified": "2026-10-23T13:17:19.387",
        "metrics": {},
        "published": "2026-10-23T13:17:19.387",
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        "vulnStatus": "Received"
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  }
}



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