GHSA-MFHV-3JVW-9W4G
Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-15 06:32In the Linux kernel, the following vulnerability has been resolved:
net/sched: sch_hfsc: Don't make class passive twice
update_vf() is called from two places for the same class during a single dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last packets while dequeuing:
-
The child calls qdisc_tree_reduce_backlog(), which, now that the child is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns the class passive (cl_nactive is decremented up the hierarchy).
-
hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time) to charge the dequeued bytes.
On the second call the class is already passive, but its child qdisc is still empty, so update_vf() arms go_passive again:
if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC)
go_passive = 1;
The leaf is then skipped by the cl_nactive == 0 check inside the loop, which does not clear go_passive, so the stale go_passive propagates to the parent and decrements its cl_nactive a second time. A parent that still has other active children is driven to cl_nactive == 0 and removed from the vttree, even though those siblings are still backlogged. They are never dequeued again and the qdisc stalls.
Fix this by only arming go_passive when the class is actually active, so an already-passive class no longer triggers a second passive transition. The byte accounting (cl->cl_total += len) still runs for every ancestor, so dequeued bytes continue to be counted exactly once.
{
"affected": [],
"aliases": [
"CVE-2026-74284"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-15T06:22:27Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_hfsc: Don\u0027t make class passive twice\n\nupdate_vf() is called from two places for the same class during a single\ndequeue when the class\u0027s child qdisc (e.g. codel/fq_codel) drops its last\npackets while dequeuing:\n\n1. The child calls qdisc_tree_reduce_backlog(), which, now that the child\n is empty, invokes hfsc_qlen_notify() -\u003e update_vf(cl, 0, 0) and turns\n the class passive (cl_nactive is decremented up the hierarchy).\n\n2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time)\n to charge the dequeued bytes.\n\nOn the second call the class is already passive, but its child qdisc is\nstill empty, so update_vf() arms go_passive again:\n\n if (cl-\u003eqdisc-\u003eq.qlen == 0 \u0026\u0026 cl-\u003ecl_flags \u0026 HFSC_FSC)\n go_passive = 1;\n\nThe leaf is then skipped by the cl_nactive == 0 check inside the loop,\nwhich does not clear go_passive, so the stale go_passive propagates to the\nparent and decrements its cl_nactive a second time. A parent that still\nhas other active children is driven to cl_nactive == 0 and removed from\nthe vttree, even though those siblings are still backlogged. They are\nnever dequeued again and the qdisc stalls.\n\nFix this by only arming go_passive when the class is actually active, so an\nalready-passive class no longer triggers a second passive transition. The\nbyte accounting (cl-\u003ecl_total += len) still runs for every ancestor, so\ndequeued bytes continue to be counted exactly once.",
"id": "GHSA-mfhv-3jvw-9w4g",
"modified": "2026-08-15T06:32:28Z",
"published": "2026-08-15T06:32:28Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74284"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/15720cd8fa3fc625146128f89a8e11b0449a20a7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3a49bbae676fef1ffe548971e6229ae2adeb9d10"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/66dbb13eeb2fc339f8f548a9076be4c1a94857b0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/90b662ea25f5e83bb3b8ccec5b93ced810b92fb8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9221a594c72a1446137926d4c2aa04e345f798dc"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a425c82ff06cda5165e0de3de8c2a445ec1f863e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b2a017bfcf565721918ec7355a373911d2f2a227"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fc973ecd1a079b9a87c360478542f3a56dea085b"
}
],
"schema_version": "1.4.0",
"severity": []
}
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