CVE-2025-39905

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: net: phylink: add lock for serializing concurrent pl->phydev writes with resolver Currently phylink_resolve() protects itself against concurrent phylink_bringup_phy() or phylink_disconnect_phy() calls which modify pl->phydev by relying on pl->state_mutex. The problem is that in phylink_resolve(), pl->state_mutex is in a lock inversion state with pl->phydev->lock. So pl->phydev->lock needs to be acquired prior to pl->state_mutex. But that requires dereferencing pl->phydev in the first place, and without pl->state_mutex, that is racy. Hence the reason for the extra lock. Currently it is redundant, but it will serve a functional purpose once mutex_lock(&phy->lock) will be moved outside of the mutex_lock(&pl->state_mutex) section. Another alternative considered would have been to let phylink_resolve() acquire the rtnl_mutex, which is also held when phylink_bringup_phy() and phylink_disconnect_phy() are called. But since phylink_disconnect_phy() runs under rtnl_lock(), it would deadlock with phylink_resolve() when calling flush_work(&pl->resolve). Additionally, it would have been undesirable because it would have unnecessarily blocked many other call paths as well in the entire kernel, so the smaller-scoped lock was preferred.

Severity

HIGH

CVSS score

7.0 (v3.1)

Vulnerability status

Modified

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2025-10-01 08:15:33.370000

Last modified

2026-10-19 21:10:00.160000

View original CVE JSON

{
  "id": "CVE-2025-39905",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2025-10-01T08:15:33.370",
  "lastModified": "2026-10-19T21:10:00.160",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: phylink: add lock for serializing concurrent pl->phydev writes with resolver\n\nCurrently phylink_resolve() protects itself against concurrent\nphylink_bringup_phy() or phylink_disconnect_phy() calls which modify\npl->phydev by relying on pl->state_mutex.\n\nThe problem is that in phylink_resolve(), pl->state_mutex is in a lock\ninversion state with pl->phydev->lock. So pl->phydev->lock needs to be\nacquired prior to pl->state_mutex. But that requires dereferencing\npl->phydev in the first place, and without pl->state_mutex, that is\nracy.\n\nHence the reason for the extra lock. Currently it is redundant, but it\nwill serve a functional purpose once mutex_lock(&phy->lock) will be\nmoved outside of the mutex_lock(&pl->state_mutex) section.\n\nAnother alternative considered would have been to let phylink_resolve()\nacquire the rtnl_mutex, which is also held when phylink_bringup_phy()\nand phylink_disconnect_phy() are called. But since phylink_disconnect_phy()\nruns under rtnl_lock(), it would deadlock with phylink_resolve() when\ncalling flush_work(&pl->resolve). Additionally, it would have been\nundesirable because it would have unnecessarily blocked many other call\npaths as well in the entire kernel, so the smaller-scoped lock was\npreferred."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnet: phylink: añadir un bloqueo para serializar escrituras concurrentes de pl->phydev con el resolvedor\n\nActualmente, phylink_resolve() se protege contra llamadas concurrentes a phylink_bringup_phy() o phylink_disconnect_phy() que modifican pl->phydev al depender de pl->state_mutex.\n\nEl problema es que en phylink_resolve(), pl->state_mutex está en un estado de inversión de bloqueo con pl->phydev->lock. Así que pl->phydev->lock necesita ser adquirido antes de pl->state_mutex. Pero eso requiere desreferenciar pl->phydev en primer lugar, y sin pl->state_mutex, eso es propenso a condiciones de carrera.\n\nDe ahí la razón del bloqueo adicional. Actualmente es redundante, pero servirá un propósito funcional una vez que mutex_lock(&phy->lock) sea movido fuera de la sección mutex_lock(&pl->state_mutex).\n\nOtra alternativa considerada habría sido permitir que phylink_resolve() adquiera el rtnl_mutex, el cual también se mantiene cuando se llaman a phylink_bringup_phy() y phylink_disconnect_phy(). Pero dado que phylink_disconnect_phy() se ejecuta bajo rtnl_lock(), entraría en interbloqueo con phylink_resolve() al llamar a flush_work(&pl->resolve). Además, habría sido indeseable porque habría bloqueado innecesariamente muchas otras rutas de llamada también en todo el kernel, por lo que se prefirió el bloqueo de alcance más pequeño."
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