### [CVE-2025-38457](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-38457)
![](https://img.shields.io/static/v1?label=Product&message=Linux&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=2.6.20%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=n%2Fa&color=blue)

### Description

In the Linux kernel, the following vulnerability has been resolved:net/sched: Abort __tc_modify_qdisc if parent class does not existLion's patch [1] revealed an ancient bug in the qdisc API.Whenever a user creates/modifies a qdisc specifying as a parent anotherqdisc, the qdisc API will, during grafting, detect that the user isnot trying to attach to a class and reject. However grafting isperformed after qdisc_create (and thus the qdiscs' init callback) isexecuted. In qdiscs that eventually call qdisc_tree_reduce_backlogduring init or change (such as fq, hhf, choke, etc), an issuearises. For example, executing the following commands:sudo tc qdisc add dev lo root handle a: htb default 2sudo tc qdisc add dev lo parent a: handle beef fqQdiscs such as fq, hhf, choke, etc unconditionally invokeqdisc_tree_reduce_backlog() in their control path init() or change() whichthen causes a failure to find the child class; however, that does not stopthe unconditional invocation of the assumed child qdisc's qlen_notify witha null class. All these qdiscs make the assumption that class is non-null.The solution is ensure that qdisc_leaf() which looks up the parentclass, and is invoked prior to qdisc_create(), should return failure onnot finding the class.In this patch, we leverage qdisc_leaf to return ERR_PTRs whenever theparentid doesn't correspond to a class, so that we can detect itearlier on and abort before qdisc_create is called.[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/

### POC

#### Reference
No PoCs from references.

#### Github
- https://github.com/w4zu/Debian_security