{"id":"CVE-2025-38457","state":"PUBLISHED","title":"net/sched: Abort __tc_modify_qdisc if parent class does not exist","description":"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/","publishedAt":"2025-07-25T15:27:36.226Z","updatedAt":"2026-10-15T01:07:17.428Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"923a276c74e25073ae391e930792ac86a9f77f1e","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"90436e72c9622c2f70389070088325a3232d339f","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"25452638f133ac19d75af3f928327d8016952c8e","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"23c165dde88eac405eebb59051ea1fe139a45803","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"8ecd651ef24ab50123692a4e3e25db93cb11602a","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"e28a383d6485c3bb51dc5953552f76c4dea33eea","versionType":"git"},{"version":"5e50da01d0ce7ef0ba3ed6cfabd62f327da0aca6","status":"affected","lessThan":"ffdde7bf5a439aaa1955ebd581f5c64ab1533963","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_api.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.20","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.20","versionType":"semver"},{"version":"5.4.296","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.240","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.189","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.146","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.99","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.39","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.15.7","status":"unaffected","lessThanOrEqual":"6.15.*","versionType":"semver"},{"version":"6.16","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_api.c"]}],"references":["https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1e","https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f","https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e","https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803","https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af","https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a","https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eea","https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963","https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html","https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html","https://cert-portal.siemens.com/productcert/html/ssa-082556.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/38xxx/CVE-2025-38457.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-38457","state":"PUBLISHED","datePublished":"2025-07-25T15:27:36.226Z","dateUpdated":"2026-10-15T01:07:17.428Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T04:51:24.019Z"},"containers":{"cna":{"title":"net/sched: Abort __tc_modify_qdisc if parent class does not exist","descriptions":[{"lang":"en","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'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] 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