CVE-2026-90058 (GCVE-0-2026-90058)
Vulnerability from cvelistv5
Published
2026-09-17 16:05
Modified
2026-10-19 08:57
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup qdisc_get_stab() accepts a user-supplied size table, and __qdisc_calculate_pkt_len() amplifies qdisc_pkt_len() through the overhead, the size-table data (u16), and size_log (up to STAB_SIZE_LOG_MAX). A crafted stab can therefore set qdisc_pkt_len() to ~1 GiB for an ordinary skb. Per-flow deficit schedulers such as DRR and ETS replenish one quantum per loop iteration; with a tiny quantum (1) they spin billions of times under the qdisc lock, producing a soft lockup / RCU stall as illustrated by vega@nebusec.ai. Cap the final qdisc_pkt_len() to QDISC_PKT_LEN_MAX so the size-table amplification cannot drive deficit schedulers into an unbounded loop. A legitimate size table (e.g. qfq's overhead 999999999, which is handled by dropping) is still accepted. Introduce cap QDISC_PKT_LEN_MAX (1 << 20) = 1 MiB which is well above any legitimate single-skb wire length: the largest current skb->len is GSO_MAX_SIZE (524280), and an ATM-style size table (53/48 cell tax) amplifies that to ~578 KB, both comfortably below 1 MiB. At the same time, 1 MiB bounds the deficit refill loop to ~1M iterations per packet with quantum=1, which completes in a few milliseconds well under the demonstrated softlockup threshold (~10^9 iterations). Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_NET_SCH_DRR=y (or CONFIG_NET_SCH_ETS=y). - Attach a DRR (or ETS) root qdisc with a crafted TCA_STAB that amplifies qdisc_pkt_len to ~1 GiB (e.g. size_log=15, data=[32768]). - Add a class with a tiny quantum of 1 and send one small packet; the deficit loop spins billions of times under the qdisc lock and trips the softlockup detector (panic with kernel.softlockup_panic=1). - Reachable as root or from an unprivileged user in a fresh user+net namespace (unshare -Urn) with namespace-local CAP_NET_ADMIN.
References
Impacted products
Vendor Product Version
Linux Linux Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
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{
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          "programFiles": [
            "include/net/pkt_sched.h",
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "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\u0027s overhead 999999999, which is\nhandled by dropping) is still accepted.\n\nIntroduce cap QDISC_PKT_LEN_MAX (1 \u003c\u003c 20) = 1 MiB which is well above\nany legitimate single-skb wire length: the largest current skb-\u003elen\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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:57:15.626Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4f0f4b09a95ef602fbdae948326beadd9c20eab3"
        },
        {
          "url": "https://git.kernel.org/stable/c/0bc5a6280a132a2170c6fa742436e01b635f02de"
        },
        {
          "url": "https://git.kernel.org/stable/c/448c34421b38ec7c93a0060a885218ca319d382b"
        },
        {
          "url": "https://git.kernel.org/stable/c/82fdbf49b9f7528c82bf608cfa9710e5f81a198c"
        },
        {
          "url": "https://git.kernel.org/stable/c/6e78792d8ce1fa3561713860ee8086901dde4f99"
        },
        {
          "url": "https://git.kernel.org/stable/c/1a5c26e586481bc82abc19ac92c3d9f10518f525"
        },
        {
          "url": "https://git.kernel.org/stable/c/16d21a27df3f50b7251c9388fc5a7ab22703b469"
        },
        {
          "url": "https://git.kernel.org/stable/c/8f735d64382dcf162f4276d6699d03ad2f859c0b"
        }
      ],
      "title": "net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup",
      "x_generator": {
        "engine": "bippy-1.2.0"
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90058",
    "datePublished": "2026-09-17T16:05:43.184Z",
    "dateReserved": "2026-09-11T19:38:34.784Z",
    "dateUpdated": "2026-10-19T08:57:15.626Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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