{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2023-54107",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2023-54107"
  ],
  "published": "2025-12-24T13:11:50Z",
  "summary": "blk-cgroup: dropping parent refcount after pd_free_fn() is done",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: dropping parent refcount after pd_free_fn() is done\n\nSome cgroup policies will access parent pd through child pd even\nafter pd_offline_fn() is done. If pd_free_fn() for parent is called\nbefore child, then UAF can be triggered. Hence it's better to guarantee\nthe order of pd_free_fn().\n\nCurrently refcount of parent blkg is dropped in __blkg_release(), which\nis before pd_free_fn() is called in blkg_free_work_fn() while\nblkg_free_work_fn() is called asynchronously.\n\nThis patch make sure pd_free_fn() called from removing cgroup is ordered\nby delaying dropping parent refcount after calling pd_free_fn() for\nchild.\n\nBTW, pd_free_fn() will also be called from blkcg_deactivate_policy()\nfrom deleting device, and following patches will guarantee the order.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
  "affected": [
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        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
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        "1:6.1.58-1+rpt2",
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2023-54107"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c7241babf0855d8a6180cd1743ff0ec34de40b4e"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T11:24:39Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - Triggering requires local cgroup filesystem operations (mkdir/rmdir of nested cgroups, writes to io.max/io.weight/io.latency) plus block I/O to populate blkgs. There is no remote or adjacent-network path into blk-cgroup teardown.\nAC:L - Although the UAF arises from unordered asynchronous work items and timers, the attacker controls both sides \u2014 building the nested blkcg hierarchy, choosing the tear-down order and timing, looping thousands of create/destroy cycles, and loading system_wq to widen the window while pd_free_fn sleeps (hrtimer_cancel, blk_put_queue). The iocost/throttle timers also fire on their own, so the window recurs without any condition outside attacker influence.\nPR:L - An unprivileged local account with a delegated cgroup v2 subtree suffices \u2014 standard systemd user slices and rootless/OCI containers grant mkdir/rmdir plus ownership of the non-root io.max, io.weight and io.latency files in cgroups the user creates, and bfq/blk-throttle policies are active without any privileged setup. No real root in the initial namespace is needed.\nUI:N - The attacker performs the entire sequence \u2014 cgroup creation, I/O generation, and rmdir \u2014 in its own process with no action by any other user.\nS:U - The corruption is confined to kernel heap objects managed by the same kernel security authority; no VM, hypervisor, or IOMMU boundary is crossed.\nC:H - The freed parent ioc_gq/throtl_grp/bfq_group lives in a general kmalloc cache, and __propagate_weights()/current_hweight() read child_active_sum, child_inuse_sum, active and inuse straight out of the reclaimed slot, with results observable via io.stat and scheduling behaviour. Heap grooming turns this into a controllable kernel-memory disclosure primitive.\nI:H - __propagate_weights() performs read-modify-write arithmetic directly on the freed parent object (parent->child_active_sum += ..., parent->child_inuse_sum += ...) with deltas derived from attacker-chosen io.weight values, and throtl_rb_erase() writes rb-tree pointers into the freed parent service queue. Sprayed into an attacker-chosen reclaimed object, this is a write primitive leading to control-flow hijack and privilege escalation.\nA:H - Use-after-free access and modification of freed slab memory reliably produces KASAN splats, rb-tree/slab corruption, and kernel oops or panic, and the sequence can be repeated at will to crash the machine."
    }
  }
}