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CVE-2025-38017

Estado: AnalizadaMedia (5.5)—

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:

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.

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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].

Detalles técnicos trazas, registros y código del informe original
```
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);
}
```

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2025-38017",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 5.5,
          "attackVector": "LOCAL",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 1.8
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          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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              "lessThan": "7631dca012593c95d36199082546a24a0058fc50",
              "versionType": "git"
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          "vendor": "Linux",
          "product": "Linux",
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              "version": "6.14.4",
              "lessThan": "6.14.8",
              "versionType": "semver"
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          "programFiles": [
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          "defaultStatus": "unaffected"
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  "published": "2025-06-18T10:15:33.310",
  "references": [
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      "url": "https://git.kernel.org/stable/c/7631dca012593c95d36199082546a24a0058fc50",
      "tags": [
        "Patch"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d9ec73301099ec5975505e1c3effbe768bab9490",
      "tags": [
        "Patch"
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
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  "vulnStatus": "Analyzed",
  "weaknesses": [
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      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "NVD-CWE-noinfo"
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      ]
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  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/eventpoll: fix endless busy loop after timeout has expired\n\nAfter commit 0a65bc27bd64 (\"eventpoll: Set epoll timeout if it's in\nthe future\"), the following program would immediately enter a busy\nloop in the kernel:\n\n```\nint main() {\n  int e = epoll_create1(0);\n  struct epoll_event event = {.events = EPOLLIN};\n  epoll_ctl(e, EPOLL_CTL_ADD, 0, &event);\n  const struct timespec timeout = {.tv_nsec = 1};\n  epoll_pwait2(e, &event, 1, &timeout, 0);\n}\n```\n\nThis happens because the given (non-zero) timeout of 1 nanosecond\nusually expires before ep_poll() is entered and then\nep_schedule_timeout() returns false, but `timed_out` is never set\nbecause the code line that sets it is skipped.  This quickly turns\ninto a soft lockup, RCU stalls and deadlocks, inflicting severe\nheadaches to the whole system.\n\nWhen the timeout has expired, we don't need to schedule a hrtimer, but\nwe should set the `timed_out` variable.  Therefore, I suggest moving\nthe ep_schedule_timeout() check into the `timed_out` expression\ninstead of skipping it.\n\nbrauner: Note that there was an earlier fix by Joe Damato in response to\nmy bug report in [1]."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: fs/eventpoll: corrige un bucle ocupado sin fin después de que expira el tiempo de espera Después de el commit 0a65bc27bd64 (\"eventpoll: establece el tiempo de espera de epoll si es en el futuro\"), el siguiente programa ingresaría inmediatamente en un bucle ocupado en el 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); } ``` Esto sucede porque el tiempo de espera dado (distinto de cero) de 1 nanosegundo generalmente expira antes de que se ingrese ep_poll() y luego ep_schedule_timeout() devuelve falso, pero `timed_out` nunca se establece porque se omite la línea de código que lo establece. Esto rápidamente se convierte en un bloqueo suave, RCU se bloquea y se bloquea, lo que inflige graves dolores de cabeza a todo el sistema. Cuando el tiempo de espera ha expirado, no necesitamos programar un hrtimer, pero debemos establecer la variable `timed_out`. Por lo tanto, sugiero mover la comprobación de ep_schedule_timeout() a la expresión `timed_out` en lugar de omitirla. brauner: Tenga en cuenta que hubo una corrección anterior por Joe Damato en respuesta a mi informe de error en [1]."
    }
  ],
  "lastModified": "2026-06-17T09:15:53.390",
  "configurations": [
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      "nodes": [
        {
          "negate": false,
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}