{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-38306",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-38306"
  ],
  "published": "2025-07-10T07:42:34Z",
  "summary": "fs/fhandle.c: fix a race in call of has_locked_children()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/fhandle.c: fix a race in call of has_locked_children()\n\nmay_decode_fh() is calling has_locked_children() while holding no locks.\nThat's an oopsable race...\n\nThe rest of the callers are safe since they are holding namespace_sem and\nare guaranteed a positive refcount on the mount in question.\n\nRename the current has_locked_children() to __has_locked_children(), make\nit static and switch the fs/namespace.c users to it.\n\nMake has_locked_children() a wrapper for __has_locked_children(), calling\nthe latter under read_seqlock_excl(&mount_lock).",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-38306"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/6482c3dccbfb8d20e2856ce67c75856859930b3f"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/287c7d34eedd37af1272dfb3b6e8656f4f026424"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/1f282cdc1d219c4a557f7009e81bc792820d9d9a"
    }
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    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T12:19:11Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The vulnerability is reached through local syscalls \u2014 `open_by_handle_at(2)` drives the unlocked `has_locked_children()` traversal while `mount(2)`/`umount(2)` mutate the `mnt_mounts` list. No network or physical access is involved.\nAC:L - The attacker controls both sides of the race entirely, spinning one thread on `open_by_handle_at(..., O_DIRECTORY)` and another on bind-mount/umount in their own mount namespace; the check runs before the file handle is even copied in or validated, so the window can be hammered without needing a valid handle or any condition outside attacker control.\nPR:L - An unprivileged local user reaches the vulnerable call by running `unshare -Urm`, since the gate only needs `CAP_SYS_ADMIN` over the mount namespace's owning user namespace \u2014 which is the attacker's own newly created user namespace. It is likewise reachable by any process that is root inside an ordinary container.\nUI:N - The attacker triggers everything from their own threads; no victim action, mount, or file access by another user is required.\nS:U - The corrupted state and the resulting impact are both within the kernel's own security authority, with no crossing of a VM, hypervisor, or IOMMU boundary.\nC:H - Traversing the concurrently modified list reads freed `struct mount` memory and feeds a stale `mnt_mountpoint` into `is_subdir()`/`d_ancestor()`, chasing attacker-groomable pointers; additionally, a raced result defeats the locked-mount gate, granting `HANDLE_CHECK_SUBTREE` and letting the attacker open directory handles into subtrees deliberately hidden by locked mounts.\nI:H - The use-after-free is on `mnt_cache` objects the attacker can spray at will via `mount()`, the standard basis for heap-corruption and control-flow primitives; the same bypass also yields a writable directory fd anchor beneath mounts that locking was meant to protect.\nA:H - `list_del_init()` on a mount being unmounted leaves a self-referential entry, trapping the unsynchronized traverser in an unkillable in-kernel infinite loop (soft/hard lockup), and the freed-mount dereference produces an oops \u2014 Al Viro describes it as \"an oopsable race.\""
    }
  }
}