CVE-2025-38457 MEDIUM

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/[email protected]/

Additional Descriptions (1)

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] reveló 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 después de ejecutar qdisc_create (y, por lo tanto, la devolución de llamada de inicio de la qdisc). En las qdisc que eventualmente llaman a qdisc_tree_reduce_backlog durante la inicialización 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 invocación incondicional de qlen_notify de la qdisc hija asumida con una clase nula. Todas estas qdisc asumen que la clase no es nula. La solución 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/[email protected]/

Source	Type	Description
[email protected]	Primary	en NVD-CWE-noinfo

• https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1e
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eea
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
  Source: af854a3a-2127-422b-91ae-364da2661108
  Third Party Advisory
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
  Source: af854a3a-2127-422b-91ae-364da2661108
  Third Party Advisory
• https://cert-portal.siemens.com/productcert/html/ssa-082556.html
  Source: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e