{"cve":"CVE-2026-90058","nvd":{"published":"2026-09-17T17:16:54.440","modified":"2026-10-19T09:18:54.147","status":"Received","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: bound qdisc_pkt_len to prevent qdisc soft lockup\n\nqdisc_get_stab() accepts a user-supplied size table, and\n__qdisc_calculate_pkt_len() amplifies qdisc_pkt_len() through the\noverhead, the size-table data (u16), and size_log (up to\nSTAB_SIZE_LOG_MAX). A crafted stab can therefore set qdisc_pkt_len()\nto ~1 GiB for an ordinary skb. Per-flow deficit schedulers such as\nDRR and ETS replenish one quantum per loop iteration; with a tiny\nquantum (1) they spin billions of times under the qdisc lock,\nproducing a soft lockup / RCU stall as illustrated by vega@nebusec.ai.\n\nCap the final qdisc_pkt_len() to QDISC_PKT_LEN_MAX so the size-table\namplification cannot drive deficit schedulers into an unbounded loop.\nA legitimate size table (e.g. qfq's overhead 999999999, which is\nhandled by dropping) is still accepted.\n\nIntroduce cap QDISC_PKT_LEN_MAX (1 << 20) = 1 MiB which is well above\nany legitimate single-skb wire length: the largest current skb->len\nis GSO_MAX_SIZE (524280), and an ATM-style size table (53/48 cell tax)\namplifies that to ~578 KB, both comfortably below 1 MiB. At the same\ntime, 1 MiB bounds the deficit refill loop to ~1M iterations per\npacket with quantum=1, which completes in a few milliseconds well\nunder the demonstrated softlockup threshold (~10^9 iterations).\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED=y, CONFIG_NET_SCH_DRR=y (or CONFIG_NET_SCH_ETS=y).\n- Attach a DRR (or ETS) root qdisc with a crafted TCA_STAB that\n  amplifies qdisc_pkt_len to ~1 GiB (e.g. size_log=15, data=[32768]).\n- Add a class with a tiny quantum of 1 and send one small packet; the\n  deficit loop spins billions of times under the qdisc lock and trips\n  the softlockup detector (panic with kernel.softlockup_panic=1).\n- Reachable as root or from an unprivileged user in a fresh user+net\n  namespace (unshare -Urn) with namespace-local CAP_NET_ADMIN.","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/0bc5a6280a132a2170c6fa742436e01b635f02de","https://git.kernel.org/stable/c/16d21a27df3f50b7251c9388fc5a7ab22703b469","https://git.kernel.org/stable/c/1a5c26e586481bc82abc19ac92c3d9f10518f525","https://git.kernel.org/stable/c/448c34421b38ec7c93a0060a885218ca319d382b","https://git.kernel.org/stable/c/4f0f4b09a95ef602fbdae948326beadd9c20eab3"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:55:23.253742848+00:00"},"epss":{"cve":"CVE-2026-90058","score":0.00216,"percentile":0.1196,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}