net_sched: gen_estimator: fix est_timer() vs CONFIG_PREEMPT_RT=y

{
  "id": "a4c7c93911448a73b4182330ffde22049f1b7c7e9a7f2a3b04e318b763e3d46b",
  "url": "https://osv.dev/vulnerability/CVE-2025-39900",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net_sched: gen_estimator: fix est_timer() vs CONFIG_PREEMPT_RT=y",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net_sched: gen_estimator: fix est_timer() vs CONFIG_PREEMPT_RT=y syzbot reported a WARNING in est_timer() [1] Problem here is that with CONFIG_PREEMPT_RT=y, timer callbacks can be preempted. Adopt preempt_disable_nested()/preempt_enable_nested() to fix this. [1] WARNING: CPU: 0 PID: 16 at ./include/linux/seqlock.h:221 __seqprop_assert include/linux/seqlock.h:221 [inline] WARNING: CPU: 0 PID: 16 at ./include/linux/seqlock.h:221 est_timer+0x6dc/0x9f0 net/core/gen_estimator.c:93 Modules linked in: CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:__seqprop_assert include/linux/seqlock.h:221 [inline] RIP: 0010:est_timer+0x6dc/0x9f0 net/core/gen_estimator.c:93 Call Trace: call_timer_fn+0x17e/0x5f0 kernel/time/timer.c:1747 expire_timers kernel/time/timer.c:1798 [inline] __run_timers kernel/time/timer.c:2372 [inline] __run_timer_base+0x648/0x970 kernel/time/timer.c:2384 run_timer_base kernel/time/timer.c:2393 [inline] run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403 handle_softirqs+0x22c/0x710 kernel/softirq.c:579 __do_softirq kernel/softirq.c:613 [inline] run_ktimerd+0xcf/0x190 kernel/softirq.c:1043 smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:160 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x8",
    "evidence": "osv:CVE-2025-39900",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.46",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.16.6",
            "evidence": "/affected/1/ranges"
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    "severity": "medium",
    "structured": {
      "id": "CVE-2025-39900",
      "aliases": [
        "CVE-2025-39900"
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
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              "type": "ECOSYSTEM",
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                  "introduced": "6.12.0"
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            "name": "Kernel",
            "ecosystem": "Linux"
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          "database_specific": {
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      ],
      "modified": "2026-10-28T02:30:30.804147290Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/9f74c0ea9b26d1505d55b61e36b1623dd347e1d1",
        "https://git.kernel.org/stable/c/a22ec2ee824be30803068a52f78f7ffe3bc879fb",
        "https://git.kernel.org/stable/c/e79923824c48b930609680be04cb29253fc4a17d",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39900.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-39900",
        "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/2025/39xxx/CVE-2025-39900.json"
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    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 497824,
  "published_at": "2025-10-01T07:42:47.785+00:00"
}