FKIE_CVE-2025-37953

Vulnerability from fkie_nvd - Published: 2025-05-20 16:15 - Updated: 2026-06-17 09:15
Severity
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: sch_htb: make htb_deactivate() idempotent Alan reported a NULL pointer dereference in htb_next_rb_node() after we made htb_qlen_notify() idempotent. It turns out in the following case it introduced some regression: htb_dequeue_tree(): |-> fq_codel_dequeue() |-> qdisc_tree_reduce_backlog() |-> htb_qlen_notify() |-> htb_deactivate() |-> htb_next_rb_node() |-> htb_deactivate() For htb_next_rb_node(), after calling the 1st htb_deactivate(), the clprio[prio]->ptr could be already set to NULL, which means htb_next_rb_node() is vulnerable here. For htb_deactivate(), although we checked qlen before calling it, in case of qlen==0 after qdisc_tree_reduce_backlog(), we may call it again which triggers the warning inside. To fix the issues here, we need to: 1) Make htb_deactivate() idempotent, that is, simply return if we already call it before. 2) Make htb_next_rb_node() safe against ptr==NULL. Many thanks to Alan for testing and for the reproducer.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/31ff70ad39485698cf779f2078132d80b57f6c07Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3769478610135e82b262640252d90f6efb05be71Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/98cd7ed92753090a714f0802d4434314526fe61dPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/99ff8a20fd61315bf9ae627440a5ff07d22ee153Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a9945f7cf1709adc5d2d31cb6cfc85627ce299a8Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c2d25fddd867ce20a266806634eeeb5c30cb520cPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c4792b9e38d2f61b07eac72f10909fa76130314bPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c928dd4f6bf0c25c72b11824a1e9ac9bd37296a0Patch
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2025/08/msg00010.htmlThird Party Advisory
Impacted products
Vendor Product Version
linux linux_kernel 6.1.138
linux linux_kernel 6.6.90
linux linux_kernel 6.12.28
linux linux_kernel 6.14.6
linux linux_kernel 6.15
linux linux_kernel 6.15
linux linux_kernel 6.15
linux linux_kernel 6.15
debian debian_linux 11.0
To clipboard 

{
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsch_htb: make htb_deactivate() idempotent\n\nAlan reported a NULL pointer dereference in htb_next_rb_node()\nafter we made htb_qlen_notify() idempotent.\n\nIt turns out in the following case it introduced some regression:\n\nhtb_dequeue_tree():\n  |-\u003e fq_codel_dequeue()\n    |-\u003e qdisc_tree_reduce_backlog()\n      |-\u003e htb_qlen_notify()\n        |-\u003e htb_deactivate()\n  |-\u003e htb_next_rb_node()\n  |-\u003e htb_deactivate()\n\nFor htb_next_rb_node(), after calling the 1st htb_deactivate(), the\nclprio[prio]-\u003eptr could be already set to  NULL, which means\nhtb_next_rb_node() is vulnerable here.\n\nFor htb_deactivate(), although we checked qlen before calling it, in\ncase of qlen==0 after qdisc_tree_reduce_backlog(), we may call it again\nwhich triggers the warning inside.\n\nTo fix the issues here, we need to:\n\n1) Make htb_deactivate() idempotent, that is, simply return if we\n   already call it before.\n2) Make htb_next_rb_node() safe against ptr==NULL.\n\nMany thanks to Alan for testing and for the reproducer."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: sch_htb: hacer que htb_deactivate() sea idempotente. Alan inform\u00f3 una desreferencia de puntero NULL en htb_next_rb_node() despu\u00e9s de que htb_qlen_notify() fuera idempotente. Resulta que en el siguiente caso introdujo alguna regresi\u00f3n: htb_dequeue_tree(): |-\u0026gt; fq_codel_dequeue() |-\u0026gt; qdisc_tree_reduce_backlog() |-\u0026gt; htb_qlen_notify() |-\u0026gt; htb_deactivate() |-\u0026gt; htb_next_rb_node() |-\u0026gt; htb_deactivate() Para htb_next_rb_node(), despu\u00e9s de llamar al primer htb_deactivate(), el clprio[prio]-\u0026gt;ptr podr\u00eda estar ya establecido en NULL, lo que significa que htb_next_rb_node() es vulnerable aqu\u00ed. Para htb_deactivate(), aunque verificamos qlen antes de llamarlo, en caso de qlen==0 despu\u00e9s de qdisc_tree_reduce_backlog(), podemos llamarlo nuevamente, lo que activa la advertencia interna. Para solucionar estos problemas, necesitamos: 1) Hacer que htb_deactivate() sea idempotente, es decir, que simplemente regrese si ya lo llamamos. 2) Hacer que htb_next_rb_node() sea seguro contra ptr==NULL. Muchas gracias a Alan por las pruebas y por el reproductor."
    }
  ],
  "id": "CVE-2025-37953",
  "lastModified": "2026-06-17T09:15:45.963",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 5.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  },
  "published": "2025-05-20T16:15:33.483",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
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    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
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      "url": "https://lists.debian.org/debian-lts-announce/2025/08/msg00010.html"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-476"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}



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