{"id":"CVE-2026-90075","summary":"net/sched: fq_codel: clamp default quantum and mtu","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q-\u003equantum = psched_mtu(qdisc_dev(sch)) without\nclamping. A device with a huge MTU (e.g. dummy with max_mtu == 0\naccepting MTU 2147483634) makes psched_mtu() return 0x80000000, which\noverflows the signed flow-\u003edeficit to INT_MIN in fq_codel_dequeue(),\ncausing an infinite loop and soft lockup. Emulate fq_codel_change()\nand constrain to [256, FQ_CODEL_QUANTUM_MAX].\n\nThe same unclamped psched_mtu() is assigned to q-\u003ecparams.mtu a bit\nbelow, and fq_codel_change() never updates it. codel_should_drop()\ntests \"*backlog \u003c= params-\u003emtu\"; with mtu == 0x80000000 (~2 GiB) and\nthe default 32 MiB memory_limit, the test is always true, so CoDel is\nsilently and completely disabled (no drops, no ECN). Declare a single\nclamped mtu and assign both q-\u003equantum and q-\u003ecparams.mtu from it,\nwhich also removes the double psched_mtu() call.\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy\ndevice with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace.","modified":"2026-09-19T03:47:28.689059044Z","published":"2026-09-17T16:05:54.851Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/90xxx/CVE-2026-90075.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d315ee8a07fd1810880227319cf60e6cd925ef22"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585"},{"type":"WEB","url":"https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/90xxx/CVE-2026-90075.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-90075"},{"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":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe"},{"fixed":"d315ee8a07fd1810880227319cf60e6cd925ef22"},{"fixed":"a9a5b2943a00df2ab81a2209f31dd9e87016f120"},{"fixed":"3782067ec0d485628b6f1f9ede3eeeb4f611fcf2"},{"fixed":"397e2b1f71d9f15b8b4e47d24eb620e4dff8878d"},{"fixed":"324f86806673ae4a55f66d28db84577f46f615e1"},{"fixed":"dfb4b61db886917244284b18b44b23d2254b82c2"},{"fixed":"9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9"},{"fixed":"d9ebd8f9aa8b2773235889cb903fafd61f2d8585"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-90075.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.5.0"},{"fixed":"5.10.270"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.221"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.188"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.157"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.110"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.52"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-90075.json"}}],"schema_version":"1.9.0"}