{
  "cveId": "CVE-2026-98811",
  "url": "https://patchblox.com/security/cve/CVE-2026-98811",
  "summary": "CVE-2026-98811 is fixed in 39 products on 1 platform, first by DEBIAN-CVE-2026-98811, released October 19, 2026. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "net/sched: cls_api: reclaim an empty proto on the error path",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  net/sched: cls_api: reclaim an empty proto on the error path  Two racing tc filter add requests on the same chain/prio of an unlocked classifier both run change() on the shared proto and both can fail: the winner\u0027s tcf_chain_tp_delete_empty() attempt gives up because the loser\u0027s handle is still in the idr, and the loser\u0027s error path drops only its own reference without a second reclamation attempt. The empty proto stays linked in the chain, holding the chain reference, a block reference and the classifier module reference until the chain or block is torn down.  Reclaim the proto on the error path of any failed request that holds a proto reference. The reclamation is emptiness-gated: tcf_chain_tp_delete_empty() unlinks the proto only when delete_empty() admits it is empty, so a live shared proto is never unlinked. A proto the request created is reclaimed unconditionally - it is the only owner, so marking it for deletion is safe even without a delete_empty callback. Classifiers without one (the check marks the proto unconditionally) are rtnl-serialized, so the raced window this guard closes cannot arise for them.  This is a follow-up to commit d4e359b3608a (\u0022net/sched: cls_api: fix teardown of an adopted proto on insert-race loss\u0022), which stopped the loser of the insert race from unlinking the winner\u0027s live proto but left the empty-proto residual in place.  Conditions to recreate: - CONFIG_NET_CLS_FLOWER=y; veth pair - tc qdisc add dev veth0 ingress - two concurrent \u0060tc filter add dev veth0 ingress protocol ip pref 1   flower skip_sw ... action drop\u0060 (both fail in fl_hw_replace_filter   after publishing their handle in the idr); repeat in a loop - an empty flower tp stays linked after both requests fail; visible   as a bare \u0060filter protocol ip pref 1 flower chain 0\u0060 header in   \u0060tc filter show\u0060 with no filter entries - CAP_NET_ADMIN (namespace-local via unshare -Urn suffices)",
  "published": "2026-10-18T16:17:35Z",
  "severity": "Low",
  "cvss": 1.9,
  "epss": 0.00179,
  "epssPercentile": 0.07496,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "vendorAdvisory": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98811",
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