{"id":"CVE-2025-38457","title":"net/sched: Abort __tc_modify_qdisc if parent class does not exist","summary":"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's patch [1] revealed an ancient bug in the qdisc API.\nWhenever a user creates/modifies a qdisc s…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 923a276c74e25073ae391e930792ac86a9f77f1e","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 90436e72c9622c2f70389070088325a3232d339f","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 25452638f133ac19d75af3f928327d8016952c8e","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 23c165dde88eac405eebb59051ea1fe139a45803","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 8ecd651ef24ab50123692a4e3e25db93cb11602a","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < e28a383d6485c3bb51dc5953552f76c4dea33eea","Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < ffdde7bf5a439aaa1955ebd581f5c64ab1533963","Linux 2.6.20"],"published":"2025-07-25","updated":"2026-10-15","sourceUpdated":"2026-10-15T01:07:17.428Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-38457","references":[{"url":"https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1e"},{"url":"https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f"},{"url":"https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e"},{"url":"https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803"},{"url":"https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af"},{"url":"https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a"},{"url":"https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eea"},{"url":"https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963"}],"tags":["cve.org"],"epss":0.00196,"epssPercentile":0.0926,"ingestedAt":"2026-10-15T05:52:46.088Z","slug":"CVE-2025-38457","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Abort __tc_modify_qdisc if parent class does not exist\n\nLion's 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' 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's 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't 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/\n\n## Affected\n\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 923a276c74e25073ae391e930792ac86a9f77f1e`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 90436e72c9622c2f70389070088325a3232d339f`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 25452638f133ac19d75af3f928327d8016952c8e`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 23c165dde88eac405eebb59051ea1fe139a45803`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < 8ecd651ef24ab50123692a4e3e25db93cb11602a`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < e28a383d6485c3bb51dc5953552f76c4dea33eea`\n- `Linux >= 5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6 < ffdde7bf5a439aaa1955ebd581f5c64ab1533963`\n- `Linux 2.6.20`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}