net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain().

{
  "id": "8163c855d0f8d45767085f6e59b79af3a3b732a18d0b9072f41c2f51a3f6aa79",
  "url": "https://osv.dev/vulnerability/CVE-2026-97958",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain().",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain(). If a netlink socket sends RTM_GETCHAIN requests repeatedly without recv()ing the responses, tc_ctl_chain() hogs CPU and triggers Hung Task splat. [0] As caught in the stack trace, netlink_attachskb() could confuse tc_ctl_chain() by returning -EAGAIN when the userspace netlink socket's receive buffer is full. The replay: label exists since commit 32a4f5ecd738 (\"net: sched: introduce chain object to uapi\") but was not used initially. Since commit 9f407f1768d3 (\"net: sched: introduce chain templates\"), the label is needed for RTM_NEWCHAIN because tcf_proto_lookup_ops() may release RTNL to call request_module(). However, the replay logic is unnecessary for RTM_GETCHAIN. Let's apply the replay logic only for RTM_NEWCHAIN. [0]: INFO: task repro:1018 is blocked on a mutex likely owned by task repro:1022. task:repro state:R running task stack:14096 pid:1022 tgid:1014 ppid:961 task_flags:0x400040 flags:0x00080000 Call Trace: ? clockevents_program_event (kernel/time/clockevents.c:372) ? pskb_expand_head (net/core/skbuff.c:615) ? skb_release_data (net/core/skbuff.c:1122) ? netlink_attachskb (./include/linux/skbuff.h:1323 ./include/linux/skbuff.h:1332 net/netlink/af_netlink.c:1232) ? __netlink_lookup (./include/linux/rcupdate.h:882 ./include/linux/rhashtable.h:711 net/netlink/af_netlink.c:499) ? tc_chain_notify (net/sched/cls_api.c:3045) ? tc_chain_notify (",
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    "severity": "unknown",
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      "modified": "2026-10-28T02:30:24.914049172Z",
      "provider": "osv",
      "references": [
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        "https://git.kernel.org/stable/c/503ba58481e3ba69d28127d35a39cec529f9670c",
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        "https://git.kernel.org/stable/c/e9ac395bb56122a057d0aa91a6b55d9e3fa37c26",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97958.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-97958",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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    "security_relevant": true,
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  "source_id": "core-osv",
  "document_id": 491617,
  "published_at": "2026-09-25T10:23:03.753+00:00"
}