GHSA-7HWQ-JHP4-6V79

Vulnerability from github – Published: 2025-07-25 18:30 – Updated: 2026-05-12 15:30
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

net/sched: Abort __tc_modify_qdisc if parent class does not exist

Lion's patch [1] revealed an ancient bug in the qdisc API. Whenever a user creates/modifies a qdisc specifying as a parent another qdisc, the qdisc API will, during grafting, detect that the user is not trying to attach to a class and reject. However grafting is performed after qdisc_create (and thus the qdiscs' init callback) is executed. In qdiscs that eventually call qdisc_tree_reduce_backlog during init or change (such as fq, hhf, choke, etc), an issue arises. For example, executing the following commands:

sudo tc qdisc add dev lo root handle a: htb default 2 sudo tc qdisc add dev lo parent a: handle beef fq

Qdiscs such as fq, hhf, choke, etc unconditionally invoke qdisc_tree_reduce_backlog() in their control path init() or change() which then causes a failure to find the child class; however, that does not stop the unconditional invocation of the assumed child qdisc's qlen_notify with a null class. All these qdiscs make the assumption that class is non-null.

The solution is ensure that qdisc_leaf() which looks up the parent class, and is invoked prior to qdisc_create(), should return failure on not finding the class. In this patch, we leverage qdisc_leaf to return ERR_PTRs whenever the parentid doesn't correspond to a class, so that we can detect it earlier on and abort before qdisc_create is called.

[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/

Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2025-38457"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-07-25T16:15:31Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Abort __tc_modify_qdisc if parent class does not exist\n\nLion\u0027s patch [1] revealed an ancient bug in the qdisc API.\nWhenever a user creates/modifies a qdisc specifying as a parent another\nqdisc, the qdisc API will, during grafting, detect that the user is\nnot trying to attach to a class and reject. However grafting is\nperformed after qdisc_create (and thus the qdiscs\u0027 init callback) is\nexecuted. In qdiscs that eventually call qdisc_tree_reduce_backlog\nduring init or change (such as fq, hhf, choke, etc), an issue\narises. For example, executing the following commands:\n\nsudo tc qdisc add dev lo root handle a: htb default 2\nsudo tc qdisc add dev lo parent a: handle beef fq\n\nQdiscs such as fq, hhf, choke, etc unconditionally invoke\nqdisc_tree_reduce_backlog() in their control path init() or change() which\nthen causes a failure to find the child class; however, that does not stop\nthe unconditional invocation of the assumed child qdisc\u0027s qlen_notify with\na null class. All these qdiscs make the assumption that class is non-null.\n\nThe solution is ensure that qdisc_leaf() which looks up the parent\nclass, and is invoked prior to qdisc_create(), should return failure on\nnot finding the class.\nIn this patch, we leverage qdisc_leaf to return ERR_PTRs whenever the\nparentid doesn\u0027t correspond to a class, so that we can detect it\nearlier on and abort before qdisc_create is called.\n\n[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/",
  "id": "GHSA-7hwq-jhp4-6v79",
  "modified": "2026-05-12T15:30:58Z",
  "published": "2025-07-25T18:30:40Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38457"
    },
    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-082556.html"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eea"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963"
    },
    {
      "type": "WEB",
      "url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html"
    },
    {
      "type": "WEB",
      "url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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