CVE-2025-38457 (GCVE-0-2025-38457)

Vulnerability from cvelistv5 – Published: 2025-07-25 15:27 – Updated: 2025-11-03 17:38
VLAI?
Title
net/sched: Abort __tc_modify_qdisc if parent class does not exist
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/
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < 923a276c74e25073ae391e930792ac86a9f77f1e (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < 90436e72c9622c2f70389070088325a3232d339f (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < 25452638f133ac19d75af3f928327d8016952c8e (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < 23c165dde88eac405eebb59051ea1fe139a45803 (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < 4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < 8ecd651ef24ab50123692a4e3e25db93cb11602a (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < e28a383d6485c3bb51dc5953552f76c4dea33eea (git)
Affected: 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 , < ffdde7bf5a439aaa1955ebd581f5c64ab1533963 (git)
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    Linux Linux Affected: 2.6.20
Unaffected: 0 , < 2.6.20 (semver)
Unaffected: 5.4.296 , ≤ 5.4.* (semver)
Unaffected: 5.10.240 , ≤ 5.10.* (semver)
Unaffected: 5.15.189 , ≤ 5.15.* (semver)
Unaffected: 6.1.146 , ≤ 6.1.* (semver)
Unaffected: 6.6.99 , ≤ 6.6.* (semver)
Unaffected: 6.12.39 , ≤ 6.12.* (semver)
Unaffected: 6.15.7 , ≤ 6.15.* (semver)
Unaffected: 6.16 , ≤ * (original_commit_for_fix)
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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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  • 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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