{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-39508",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2024-39508"
  ],
  "published": "2024-07-12T12:21:19Z",
  "summary": "io_uring/io-wq: Use set_bit() and test_bit() at worker->flags",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/io-wq: Use set_bit() and test_bit() at worker->flags\n\nUtilize set_bit() and test_bit() on worker->flags within io_uring/io-wq\nto address potential data races.\n\nThe structure io_worker->flags may be accessed through various data\npaths, leading to concurrency issues. When KCSAN is enabled, it reveals\ndata races occurring in io_worker_handle_work and\nio_wq_activate_free_worker functions.\n\n\t BUG: KCSAN: data-race in io_worker_handle_work / io_wq_activate_free_worker\n\t write to 0xffff8885c4246404 of 4 bytes by task 49071 on cpu 28:\n\t io_worker_handle_work (io_uring/io-wq.c:434 io_uring/io-wq.c:569)\n\t io_wq_worker (io_uring/io-wq.c:?)\n<snip>\n\n\t read to 0xffff8885c4246404 of 4 bytes by task 49024 on cpu 5:\n\t io_wq_activate_free_worker (io_uring/io-wq.c:? io_uring/io-wq.c:285)\n\t io_wq_enqueue (io_uring/io-wq.c:947)\n\t io_queue_iowq (io_uring/io_uring.c:524)\n\t io_req_task_submit (io_uring/io_uring.c:1511)\n\t io_handle_tw_list (io_uring/io_uring.c:1198)\n<snip>\n\nLine numbers against commit 18daea77cca6 (\"Merge tag 'for-linus' of\ngit://git.kernel.org/pub/scm/virt/kvm/kvm\").\n\nThese races involve writes and reads to the same memory location by\ndifferent tasks running on different CPUs. To mitigate this, refactor\nthe code to use atomic operations such as set_bit(), test_bit(), and\nclear_bit() instead of basic \"and\" and \"or\" operations. This ensures\nthread-safe manipulation of worker flags.\n\nAlso, move `create_index` to avoid holes in the structure.",
  "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-2024-39508"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/ab702c3483db9046bab9f40306f1a28b22dbbdc0"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/1cbb0affb15470a9621267fe0a8568007553a4bf"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/8a565304927fbd28c9f028c492b5c1714002cbab"
    }
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  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T11:52:36Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The race is reached only through local io_uring syscalls (`io_uring_setup(2)`/`io_uring_enter(2)`) on a ring the attacker owns, via `io_queue_iowq()` \u2192 `io_wq_enqueue()` \u2192 `io_wq_activate_free_worker()`. No network or adjacent-network data path touches `io_uring/io-wq.c`.\nAC:L - The attacker controls both sides of the race: it creates the io-wq workers, forces async punting with `IOSQE_ASYNC`, and submits from multiple threads so that `io_wq_activate_free_worker()` walks `wq->free_list` on one CPU while a worker executes the non-atomic `worker->flags &= ~IO_WORKER_F_FREE` in `__io_worker_busy()` on another. The window can be hit repeatedly at no cost, exactly as KCSAN observed under ordinary load.\nPR:L - Only an unprivileged local account is required \u2014 `io_uring_setup()` performs no capability check and `sysctl_io_uring_disabled` defaults to 0, permitting io_uring for all users; io-wq worker threads are created on demand for that user's own ring.\nUI:N - The attacking task performs every step itself \u2014 creating the ring, spawning submitter threads, and queueing async work \u2014 with no action required from any other user or administrator.\nS:U - The raced state and all its consequences live in the kernel's own io-wq bookkeeping for the calling task's ring; no VM, hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - The raced field is the sole guard on `wq->free_list` membership \u2014 `io_worker_exit()` unlinks `worker->nulls_node` only `if (worker->flags & IO_WORKER_F_FREE)` before `kfree_rcu(worker, rcu)` \u2014 so an indeterminate value leaves a freed `io_worker` linked and read by `io_wq_activate_free_worker()` from other tasks, which after slab reuse discloses attacker-observable kernel heap contents through `worker->wq` and `worker->task`.\nI:H - The same stale-flag path lets other tasks operate on a freed `io_worker`: `io_worker_get()` performs `refcount_inc_not_zero` into a reallocated slab object and `wake_up_process(worker->task)` dereferences a sprayable pointer into the scheduler, yielding a write and control-flow primitive.\nA:H - A wrong `IO_WORKER_F_BOUND` read makes `io_wq_activate_free_worker()` wake a worker from the other accounting class and return true, so `io_wq_enqueue()` skips `io_wq_create_worker()` and the queued work is left with no worker to run it \u2014 an indefinite hang of the io_uring request plus `acct->nr_running` imbalance, triggerable at will by an unprivileged user."
    }
  }
}