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CVE PROGRAM SOURCE RECORDUnscored

CVE-2026-90058

net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup

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Status
Published
Published
Updated
Assigning organization
Linux

Description

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 4f0f4b09a95ef602fbdae948326beadd9c20eab3affected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 0bc5a6280a132a2170c6fa742436e01b635f02deaffected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 448c34421b38ec7c93a0060a885218ca319d382baffected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 82fdbf49b9f7528c82bf608cfa9710e5f81a198caffected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 6e78792d8ce1fa3561713860ee8086901dde4f99affected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 1a5c26e586481bc82abc19ac92c3d9f10518f525affected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 16d21a27df3f50b7251c9388fc5a7ab22703b469affected
  • 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 8f735d64382dcf162f4276d6699d03ad2f859c0baffected

Linux Linux

Default version status: affected

  • 2.6.12affected
  • 0 to < 2.6.12unaffected
  • 5.10.270 to ≤ 5.10.*unaffected
  • 5.15.221 to ≤ 5.15.*unaffected
  • 6.1.188 to ≤ 6.1.*unaffected
  • 6.6.157 to ≤ 6.6.*unaffected
  • 6.12.110 to ≤ 6.12.*unaffected
  • 6.18.52 to ≤ 6.18.*unaffected
  • 7.2.6 to ≤ 7.2.*unaffected
  • 7.3 to ≤ *unaffected

References