CVE-2026-74284 (GCVE-0-2026-74284)
Vulnerability from cvelistv5
Published
2026-08-15 05:57
Modified
2026-08-17 05:16
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In 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:
1. 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).
2. 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.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7 Version: a5efc95a33bd4fcb879250852828cc58c7862970 Version: 0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87 Version: 9030a91235ae4845ec71902c3e0cecfc9ed1f2df Version: d06476714d2819b550e0cc39222347e2c8941c9d Version: 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb Version: 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb Version: 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb Version: 9a5fd5c2f4d4afdd5e405083ee53e0789ce76956 Version: c1175c4ad01dbc9c979d099861fa90a754f72059 Version: 5.10.241 ≤ Version: 5.15.190 ≤ Version: 6.1.138 ≤ Version: 6.6.90 ≤ Version: 6.12.28 ≤ Version: 5.4.297 ≤ Version: 6.14.6 ≤ |
||
{
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"descriptions": [
{
"lang": "en",
"value": "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."
}
],
"providerMetadata": {
"dateUpdated": "2026-08-17T05:16:29.785Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/a425c82ff06cda5165e0de3de8c2a445ec1f863e"
},
{
"url": "https://git.kernel.org/stable/c/fc973ecd1a079b9a87c360478542f3a56dea085b"
},
{
"url": "https://git.kernel.org/stable/c/15720cd8fa3fc625146128f89a8e11b0449a20a7"
},
{
"url": "https://git.kernel.org/stable/c/b2a017bfcf565721918ec7355a373911d2f2a227"
},
{
"url": "https://git.kernel.org/stable/c/9221a594c72a1446137926d4c2aa04e345f798dc"
},
{
"url": "https://git.kernel.org/stable/c/66dbb13eeb2fc339f8f548a9076be4c1a94857b0"
},
{
"url": "https://git.kernel.org/stable/c/3a49bbae676fef1ffe548971e6229ae2adeb9d10"
},
{
"url": "https://git.kernel.org/stable/c/90b662ea25f5e83bb3b8ccec5b93ced810b92fb8"
}
],
"title": "net/sched: sch_hfsc: Don\u0027t make class passive twice",
"x_generator": {
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}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-74284",
"datePublished": "2026-08-15T05:57:53.290Z",
"dateReserved": "2026-08-15T05:44:03.881Z",
"dateUpdated": "2026-08-17T05:16:29.785Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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