{"id":"CVE-2025-38457","summary":"net/sched: Abort __tc_modify_qdisc if parent class does not exist","details":"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 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/","modified":"2026-04-16T00:06:06.789017711Z","published":"2025-07-25T15:27:36.226Z","related":["SUSE-SU-2025:02853-1","SUSE-SU-2025:02923-1","SUSE-SU-2025:02969-1","SUSE-SU-2025:02996-1","SUSE-SU-2025:02997-1","SUSE-SU-2025:03011-1","SUSE-SU-2025:03023-1","SUSE-SU-2025:03204-1","SUSE-SU-2025:20577-1","SUSE-SU-2025:20586-1","SUSE-SU-2025:20601-1","SUSE-SU-2025:20602-1","SUSE-SU-2025:21074-1","SUSE-SU-2025:21139-1","SUSE-SU-2025:21179-1","openSUSE-SU-2025:20081-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38457.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803"},{"type":"WEB","url":"https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eea"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38457.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-38457"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6"},{"fixed":"923a276c74e25073ae391e930792ac86a9f77f1e"},{"fixed":"90436e72c9622c2f70389070088325a3232d339f"},{"fixed":"25452638f133ac19d75af3f928327d8016952c8e"},{"fixed":"23c165dde88eac405eebb59051ea1fe139a45803"},{"fixed":"4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af"},{"fixed":"8ecd651ef24ab50123692a4e3e25db93cb11602a"},{"fixed":"e28a383d6485c3bb51dc5953552f76c4dea33eea"},{"fixed":"ffdde7bf5a439aaa1955ebd581f5c64ab1533963"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2025-38457.json"}}],"schema_version":"1.7.5"}