CVE-2026-98982 (GCVE-0-2026-98982)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:19 – Updated: 2026-10-23 12:19
VLAI
Title
namespace: don't let a pseudo dentry become the root of a mount
Summary
In the Linux kernel, the following vulnerability has been resolved: namespace: don't let a pseudo dentry become the root of a mount d_alloc_pseudo() hands out dentries for pipes, sockets and other files that are never anyone's child or parent. They carry DCACHE_NORCU and dentry_free() frees them right away because no lockless path walk can ever reach them. That holds as long as such a dentry isn't the root of a mount. But bind mounting /proc/self/fd/<fd> of such a file does exactly that. Most callers of alloc_file_pseudo() put their files on kernel-internal mounts and may_copy_tree() refuses those. bpf_token_create() doesn't. It places the token file on the bpffs mount the caller handed it and that mount is in the caller's mount namespace so the clone goes through: mount --bind /proc/self/fd/<token> <file> open_tree(tokfd, "", AT_EMPTY_PATH | OPEN_TREE_CLONE) + move_mount() __follow_mount_rcu() then loads ->mnt_root of that mount, reads d_seq and d_flags of the dentry and only then checks mount_lock. The dentry can be gone by then. The final mntput() of an unmounted parent unhooks a child that stayed attached to it under mount_lock alone. When the child's holder does the final put right after that the root is dput() and freed immediately while a walker that found the mount hashed still looks at it. Refuse to clone a mount with a DCACHE_NORCU dentry as its root. Nothing sensible can be done with a bind mount of a bpf token anyway.
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: 35f96de04127d332a5c5e8a155d31f452f88c76d , < a256e31e0c54c4c37d2523aa52faabdcdd2ebc07 (git)
Affected: 35f96de04127d332a5c5e8a155d31f452f88c76d , < 7e1c466011ba9e64d43075396badc03191bcee44 (git)
Affected: 35f96de04127d332a5c5e8a155d31f452f88c76d , < 00287afa7cd989efdbf5822b7efac33cce7d489a (git)
Affected: 35f96de04127d332a5c5e8a155d31f452f88c76d , < b138e16fb1e81376cea89f727dda7bfccd140de4 (git)
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Linux Linux Affected: 6.9
Unaffected: 0 , < 6.9 (semver)
Unaffected: 6.12.113 , ≤ 6.12.* (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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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: don\u0027t let a pseudo dentry become the root of a mount\n\nd_alloc_pseudo() hands out dentries for pipes, sockets and other files\nthat are never anyone\u0027s child or parent. They carry DCACHE_NORCU and\ndentry_free() frees them right away because no lockless path walk can\never reach them. That holds as long as such a dentry isn\u0027t the root of\na mount. But bind mounting /proc/self/fd/\u003cfd\u003e of such a file does\nexactly that.\n\nMost callers of alloc_file_pseudo() put their files on kernel-internal\nmounts and may_copy_tree() refuses those. bpf_token_create() doesn\u0027t. It\nplaces the token file on the bpffs mount the caller handed it and that\nmount is in the caller\u0027s mount namespace so the clone goes through:\n\n  mount --bind /proc/self/fd/\u003ctoken\u003e \u003cfile\u003e\n  open_tree(tokfd, \"\", AT_EMPTY_PATH | OPEN_TREE_CLONE) + move_mount()\n\n__follow_mount_rcu() then loads -\u003emnt_root of that mount, reads d_seq\nand d_flags of the dentry and only then checks mount_lock. The dentry\ncan be gone by then. The final mntput() of an unmounted parent unhooks\na child that stayed attached to it under mount_lock alone. When the\nchild\u0027s holder does the final put right after that the root is dput()\nand freed immediately while a walker that found the mount hashed still\nlooks at it.\n\nRefuse to clone a mount with a DCACHE_NORCU dentry as its root. Nothing\nsensible can be done with a bind mount of a bpf token anyway."
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    "datePublished": "2026-10-23T12:19:59.784Z",
    "dateReserved": "2026-09-25T10:25:14.384Z",
    "dateUpdated": "2026-10-23T12:19:59.784Z",
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: don\u0027t let a pseudo dentry become the root of a mount\n\nd_alloc_pseudo() hands out dentries for pipes, sockets and other files\nthat are never anyone\u0027s child or parent. They carry DCACHE_NORCU and\ndentry_free() frees them right away because no lockless path walk can\never reach them. That holds as long as such a dentry isn\u0027t the root of\na mount. But bind mounting /proc/self/fd/\u003cfd\u003e of such a file does\nexactly that.\n\nMost callers of alloc_file_pseudo() put their files on kernel-internal\nmounts and may_copy_tree() refuses those. bpf_token_create() doesn\u0027t. It\nplaces the token file on the bpffs mount the caller handed it and that\nmount is in the caller\u0027s mount namespace so the clone goes through:\n\n  mount --bind /proc/self/fd/\u003ctoken\u003e \u003cfile\u003e\n  open_tree(tokfd, \"\", AT_EMPTY_PATH | OPEN_TREE_CLONE) + move_mount()\n\n__follow_mount_rcu() then loads -\u003emnt_root of that mount, reads d_seq\nand d_flags of the dentry and only then checks mount_lock. The dentry\ncan be gone by then. The final mntput() of an unmounted parent unhooks\na child that stayed attached to it under mount_lock alone. When the\nchild\u0027s holder does the final put right after that the root is dput()\nand freed immediately while a walker that found the mount hashed still\nlooks at it.\n\nRefuse to clone a mount with a DCACHE_NORCU dentry as its root. Nothing\nsensible can be done with a bind mount of a bpf token anyway."
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        "lastModified": "2026-10-23T13:17:20.043",
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        "vulnStatus": "Received"
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}



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