FKIE_CVE-2025-38457

Vulnerability from fkie_nvd - Published: 2025-07-25 16:15 - Updated: 2025-12-22 21:49
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: 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/
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8ePatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49afPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602aPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339fPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1ePatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eeaPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963Patch
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2025/10/msg00007.htmlThird Party Advisory
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2025/10/msg00008.htmlThird Party Advisory
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel 6.16
linux linux_kernel 6.16
linux linux_kernel 6.16
linux linux_kernel 6.16
linux linux_kernel 6.16
debian debian_linux 11.0
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      "value": "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/"
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      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net/sched: Abort __tc_modify_qdisc si la clase padre no existe. El parche de Lion [1] revel\u00f3 un error antiguo en la API de qdisc. Siempre que un usuario crea o modifica una qdisc que especifica otra qdisc como padre, la API de qdisc detecta, durante el injerto, que el usuario no intenta asociarse a una clase y lo rechaza. Sin embargo, el injerto se realiza despu\u00e9s de ejecutar qdisc_create (y, por lo tanto, la devoluci\u00f3n de llamada de inicio de la qdisc). En las qdisc que eventualmente llaman a qdisc_tree_reduce_backlog durante la inicializaci\u00f3n o el cambio (como fq, hhf, choke, etc.), surge un problema. Por ejemplo, al ejecutar los siguientes comandos: sudo tc qdisc add dev lo root handle a: htb default 2 sudo tc qdisc add dev lo parent a: handle beef fq Las Qdisc como fq, hhf, choke, etc., invocan incondicionalmente qdisc_tree_reduce_backlog() en su ruta de control init() o change(), lo que provoca un error al no encontrar la clase hija; sin embargo, esto no detiene la invocaci\u00f3n incondicional de qlen_notify de la qdisc hija asumida con una clase nula. Todas estas qdisc asumen que la clase no es nula. La soluci\u00f3n es garantizar que qdisc_leaf(), que busca la clase padre y se invoca antes que qdisc_create(), devuelva un error al no encontrar la clase. En este parche, aprovechamos qdisc_leaf para devolver ERR_PTR siempre que el parentid no corresponda a una clase, de modo que podamos detectarlo antes y abortar antes de que se llame a qdisc_create. [1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/"
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  "id": "CVE-2025-38457",
  "lastModified": "2025-12-22T21:49:38.683",
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          "attackVector": "LOCAL",
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          "baseScore": 5.5,
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          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
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          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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