netfilter: ipset: fix refcount race between list:set GC and swap

{
  "id": "82b462fafcba0eb9ce718a736d04cca03a44acb6600c0e46246536007e7f8fd0",
  "url": "https://osv.dev/vulnerability/CVE-2026-74748",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "netfilter: ipset: fix refcount race between list:set GC and swap",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: netfilter: ipset: fix refcount race between list:set GC and swap __ip_set_put_byindex() resolved the index to a set pointer under RCU, then took ip_set_ref_lock in __ip_set_put() to decrement set->ref. ip_set_swap() holds that same lock while swapping both the ip_set_list slots and the two sets' ref counters, so it can interleave between the dereference and the lock acquisition, leaving the caller to decrement a set whose reference already moved to the other index and hit BUG_ON(set->ref == 0). list_set_gc() reaches this from timer softirq, which the nfnl mutex does not serialize against swap: an expiring list:set member calls list_set_del() -> ip_set_put_byindex() while IPSET_CMD_SWAP runs on the referenced sets. Resolve the index and decrement under ip_set_ref_lock, as ip_set_swap() already does, keeping the refcount tied to the index rather than to a stale set pointer. kernel BUG at net/netfilter/ipset/ip_set_core.c:685! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI RIP: 0010:ip_set_put_byindex (net/netfilter/ipset/ip_set_core.c:870) Call Trace: list_set_del (net/netfilter/ipset/ip_set_list_set.c:159) set_cleanup_entries (net/netfilter/ipset/ip_set_list_set.c:181) list_set_gc (net/netfilter/ipset/ip_set_list_set.c:578) call_timer_fn (kernel/time/timer.c:1748) __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2374) run_timer_softirq (kernel/time/timer.c:2405) Kernel panic - not syncing: Fatal exc",
    "evidence": "osv:CVE-2026-74748",
    "products": [
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        "prerequisites": [],
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    "severity": "high",
    "structured": {
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      "aliases": [
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      "metrics": [
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          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
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      "modified": "2026-10-28T02:30:42.224846312Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0c88868271653537ed443272dd8e7d13634d214b",
        "https://git.kernel.org/stable/c/20cb13a523f0a05cb2d0a7d72abae687683712e0",
        "https://git.kernel.org/stable/c/24ffcb1e1688c55fd2a505f064295cd28eac546d",
        "https://git.kernel.org/stable/c/97a01de0c6321b7210d30d0a4d60f10f561097c7",
        "https://git.kernel.org/stable/c/b0aab9dd1a348b99d75ff52765719d0cc2050630",
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        "https://git.kernel.org/stable/c/cb20da33839f28f590c99f16bafaa6151451c0e8",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74748.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-74748",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74748.json"
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        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 510104,
  "published_at": "2026-08-26T14:36:57.164+00:00"
}