{"id":"CVE-2026-90050","summary":"net/sched: fq: clamp quantum and initial_quantum in change path","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: clamp quantum and initial_quantum in change path\n\nThe fq change path accepts TCA_FQ_QUANTUM in [1, INT_MAX] and\nTCA_FQ_INITIAL_QUANTUM up to INT_MAX, while fq_init() already clamps to\n[1, 1\u003c\u003c20]. A user can override the init clamp via tc qdisc change,\nrestoring the small-quantum deficit spin that the init clamp prevents.\n\nNarrow iq_range.max to 1\u003c\u003c20 so TCA_FQ_INITIAL_QUANTUM is rejected at\nparse time. Clamp TCA_FQ_QUANTUM to [256, 1\u003c\u003c20] in fq_change() and\nfq_init() quantum to [256, 1\u003c\u003c20] for tiny-MTU devices.\n\nConditions to recreate the bug:\n  CONFIG_NET_SCH_FQ=y. Requires CAP_NET_ADMIN (namespace-local via\n  unshare -Urn suffices).\n\n  tc qdisc add dev dummy0 root fq\n  tc qdisc change dev dummy0 root fq quantum 1 stab data 32768 size_log 15 cell_log 0","modified":"2026-09-19T03:47:23.862736577Z","published":"2026-09-17T16:05:36.970Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/90xxx/CVE-2026-90050.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/094cc07f98dfe70a34e2a1923af17fd29b8cf622"},{"type":"WEB","url":"https://git.kernel.org/stable/c/72e9387884554f47b03bfd40fb8b2bf52789c68d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/798283cd0fe7ba997f67e5a917f14ab40afa8d9f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a27498d34c3f429fb6db3aa609569f8154afa175"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/90xxx/CVE-2026-90050.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-90050"},{"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":"d16dac3925be95ad46e986d4b139c9898b6e227f"},{"fixed":"a27498d34c3f429fb6db3aa609569f8154afa175"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"f6b3e3848a5fca63438984acd6d9eceac80814c1"},{"fixed":"798283cd0fe7ba997f67e5a917f14ab40afa8d9f"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"e35acd56f244d94355f9ab237c2ecc8fba5e6f04"},{"fixed":"72e9387884554f47b03bfd40fb8b2bf52789c68d"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"709f34f7c28dc4dd6c40343d101850f11e172312"},{"fixed":"094cc07f98dfe70a34e2a1923af17fd29b8cf622"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-90050.json"}}],"schema_version":"1.9.0"}