fs/eventpoll: fix endless busy loop after timeout has expired

{
  "id": "9f63f5dc7a3b0e0554522f32d0dcc685247bea382046437802d057464127cfe5",
  "url": "https://osv.dev/vulnerability/CVE-2025-38017",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fs/eventpoll: fix endless busy loop after timeout has expired",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: fs/eventpoll: fix endless busy loop after timeout has expired After commit 0a65bc27bd64 (\"eventpoll: Set epoll timeout if it's in the future\"), the following program would immediately enter a busy loop in the kernel: ``` int main() { int e = epoll_create1(0); struct epoll_event event = {.events = EPOLLIN}; epoll_ctl(e, EPOLL_CTL_ADD, 0, &event); const struct timespec timeout = {.tv_nsec = 1}; epoll_pwait2(e, &event, 1, &timeout, 0); } ``` This happens because the given (non-zero) timeout of 1 nanosecond usually expires before ep_poll() is entered and then ep_schedule_timeout() returns false, but `timed_out` is never set because the code line that sets it is skipped. This quickly turns into a soft lockup, RCU stalls and deadlocks, inflicting severe headaches to the whole system. When the timeout has expired, we don't need to schedule a hrtimer, but we should set the `timed_out` variable. Therefore, I suggest moving the ep_schedule_timeout() check into the `timed_out` expression instead of skipping it. brauner: Note that there was an earlier fix by Joe Damato in response to my bug report in [1].",
    "evidence": "osv:CVE-2025-38017",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
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        "prerequisites": [],
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      "modified": "2026-10-28T02:30:24.597715347Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/7631dca012593c95d36199082546a24a0058fc50",
        "https://git.kernel.org/stable/c/d9ec73301099ec5975505e1c3effbe768bab9490",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38017.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-38017",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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  "source_id": "core-osv",
  "document_id": 490823,
  "published_at": "2025-06-18T09:28:25.79+00:00"
}