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

Vulnerability from cvelistv5 – Published: 2026-10-23 12:19 – Updated: 2026-10-24 14:09
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
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7064 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)
guessed Create a notification for this product.
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)
guessed Create a notification for this product.
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          "programFiles": [
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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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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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              "value": "AV:L - Local bpf(BPF_TOKEN_CREATE) reaches bpf_token_create()/alloc_file_pseudo(), after which mount(MS_BIND) or open_tree(OPEN_TREE_CLONE) reaches the patched __do_loopback() on /proc/self/fd/\u003ctoken\u003e; no network protocol carries the triggering data.\nAC:L - The attacker controls creation and teardown of the token-root mount and can race cleanup_mnt()/dput() against openat() reaching __follow_mount_rcu() using concurrent threads; neither side of the race requires external timing or victim-controlled state.\nPR:L - bpf_token_create() requires CAP_BPF in the bpffs user namespace, while open_tree(OPEN_TREE_CLONE) and move_mount() require CAP_SYS_ADMIN over the mount namespace; because bpf_fs_type has FS_USERNS_MOUNT, an ordinary user can obtain these capabilities through unprivileged user and mount namespaces.\nUI:N - The attacking process performs every required action itself: mounting delegated bpffs, creating the token, cloning and tearing down mounts, and racing openat(); no victim must mount, open, or otherwise process attacker-supplied data.\nS:U - The freed dentry is consumed by __follow_mount_rcu() inside the same host kernel, yielding ordinary local kernel compromise or denial of service rather than crossing a VM, IOMMU, or separate security-authority boundary.\nC:H - cleanup_mnt() can dput() and immediately free the DCACHE_NORCU mount root while __follow_mount_rcu() still reads its d_seq, d_flags, and potentially d_op; attacker-driven dentry-cache reuse makes this kernel UAF capable of high-impact memory disclosure.\nI:H - The freed struct dentry can be reclaimed through attacker-driven dentry allocation, letting heap spraying influence fields and the d_op-\u003ed_manage dispatch consumed by __follow_mount_rcu(); this is an exploitable kernel UAF path to arbitrary modification or control-flow hijacking.\nA:H - __follow_mount_rcu() dereferences the mount root after dentry_free() has returned it immediately to dentry_cache, so poisoned or reclaimed contents can cause a kernel oops or panic, and attacker-controlled threads can repeat the race."
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        "dateUpdated": "2026-10-24T14:09:50.745Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        {
          "url": "https://git.kernel.org/stable/c/b138e16fb1e81376cea89f727dda7bfccd140de4"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98982",
    "datePublished": "2026-10-23T12:19:59.784Z",
    "dateReserved": "2026-09-25T10:25:14.384Z",
    "dateUpdated": "2026-10-24T14:09:50.745Z",
    "state": "PUBLISHED"
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      "date": "2026-10-26",
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      "percentile": "0.05461"
    },
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      "cve": "CVE-2026-98982",
      "id": "msrc_CVE-2026-98982",
      "initial_release_date": "2026-10-24T01:10:53.000Z",
      "product_status:under_investigation": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "namespace: don\u0027t let a pseudo dentry become the root of a mount",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-98982.json",
      "version": "1"
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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."
          }
        ],
        "id": "CVE-2026-98982",
        "lastModified": "2026-10-24T14:16:50.850",
        "metrics": {
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                "attackVector": "LOCAL",
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                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
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              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
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    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-10-24T16:31:54Z",
      "cve": "CVE-2026-98982",
      "id": "CVE-2026-98982",
      "initial_release_date": "2026-10-23T23:52:21Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-98982",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-98982.json",
      "version": "3"
    }
  }
}



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