CVE-2025-39749 (GCVE-0-2025-39749)

Vulnerability from cvelistv5 – Published: 2025-09-11 16:52 – Updated: 2026-05-12 12:06
VLAI
Title
rcu: Protect ->defer_qs_iw_pending from data race
Summary
In the Linux kernel, the following vulnerability has been resolved: rcu: Protect ->defer_qs_iw_pending from data race On kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is invoked within an interrupts-disabled region of code [1], it will invoke rcu_read_unlock_special(), which uses an irq-work handler to force the system to notice when the RCU read-side critical section actually ends. That end won't happen until interrupts are enabled at the soonest. In some kernels, such as those booted with rcutree.use_softirq=y, the irq-work handler is used unconditionally. The per-CPU rcu_data structure's ->defer_qs_iw_pending field is updated by the irq-work handler and is both read and updated by rcu_read_unlock_special(). This resulted in the following KCSAN splat: ------------------------------------------------------------------------ BUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special read to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8: rcu_read_unlock_special+0x175/0x260 __rcu_read_unlock+0x92/0xa0 rt_spin_unlock+0x9b/0xc0 __local_bh_enable+0x10d/0x170 __local_bh_enable_ip+0xfb/0x150 rcu_do_batch+0x595/0xc40 rcu_cpu_kthread+0x4e9/0x830 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 write to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8: rcu_preempt_deferred_qs_handler+0x1e/0x30 irq_work_single+0xaf/0x160 run_irq_workd+0x91/0xc0 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 no locks held by irq_work/8/88. irq event stamp: 200272 hardirqs last enabled at (200272): [<ffffffffb0f56121>] finish_task_switch+0x131/0x320 hardirqs last disabled at (200271): [<ffffffffb25c7859>] __schedule+0x129/0xd70 softirqs last enabled at (0): [<ffffffffb0ee093f>] copy_process+0x4df/0x1cc0 softirqs last disabled at (0): [<0000000000000000>] 0x0 ------------------------------------------------------------------------ The problem is that irq-work handlers run with interrupts enabled, which means that rcu_preempt_deferred_qs_handler() could be interrupted, and that interrupt handler might contain an RCU read-side critical section, which might invoke rcu_read_unlock_special(). In the strict KCSAN mode of operation used by RCU, this constitutes a data race on the ->defer_qs_iw_pending field. This commit therefore disables interrupts across the portion of the rcu_preempt_deferred_qs_handler() that updates the ->defer_qs_iw_pending field. This suffices because this handler is not a fast path.
Severity
7.0 (High)
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6856 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < 74f58f382a7c8333f8d09701aefaa25913bdbe0e (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < f937759c7432d6151b73e1393b6517661813d506 (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < 0ad84d62217488e679ecc90e8628980dcc003de3 (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < b5de8d80b5d049f051b95d9b1ee50ae4ab656124 (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < b55947b725f190396f475d5d0c59aa855a4d8895 (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < e35e711c78c8a4c43330c0dcb1c4d507a19c20f4 (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < 90de9c94ea72327cfa9c2c9f6113c23a513af60b (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < 55e11f6776798b27cf09a7aa0d718415d4fc9cf5 (git)
Affected: 0864f057b050bc6dd68106b3185e02db5140012d , < 90c09d57caeca94e6f3f87c49e96a91edd40cbfd (git)
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Linux Linux Affected: 5.3
Unaffected: 0 , < 5.3 (semver)
Unaffected: 5.4.297 , ≤ 5.4.* (semver)
Unaffected: 5.10.241 , ≤ 5.10.* (semver)
Unaffected: 5.15.190 , ≤ 5.15.* (semver)
Unaffected: 6.1.149 , ≤ 6.1.* (semver)
Unaffected: 6.6.103 , ≤ 6.6.* (semver)
Unaffected: 6.12.43 , ≤ 6.12.* (semver)
Unaffected: 6.15.11 , ≤ 6.15.* (semver)
Unaffected: 6.16.2 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Siemens SIMATIC CN 4100 Affected: 0 , < V5.0 (custom)
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrcu: Protect -\u003edefer_qs_iw_pending from data race\n\nOn kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is\ninvoked within an interrupts-disabled region of code [1], it will invoke\nrcu_read_unlock_special(), which uses an irq-work handler to force the\nsystem to notice when the RCU read-side critical section actually ends.\nThat end won\u0027t happen until interrupts are enabled at the soonest.\n\nIn some kernels, such as those booted with rcutree.use_softirq=y, the\nirq-work handler is used unconditionally.\n\nThe per-CPU rcu_data structure\u0027s -\u003edefer_qs_iw_pending field is\nupdated by the irq-work handler and is both read and updated by\nrcu_read_unlock_special().  This resulted in the following KCSAN splat:\n\n------------------------------------------------------------------------\n\nBUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special\n\nread to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8:\n rcu_read_unlock_special+0x175/0x260\n __rcu_read_unlock+0x92/0xa0\n rt_spin_unlock+0x9b/0xc0\n __local_bh_enable+0x10d/0x170\n __local_bh_enable_ip+0xfb/0x150\n rcu_do_batch+0x595/0xc40\n rcu_cpu_kthread+0x4e9/0x830\n smpboot_thread_fn+0x24d/0x3b0\n kthread+0x3bd/0x410\n ret_from_fork+0x35/0x40\n ret_from_fork_asm+0x1a/0x30\n\nwrite to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8:\n rcu_preempt_deferred_qs_handler+0x1e/0x30\n irq_work_single+0xaf/0x160\n run_irq_workd+0x91/0xc0\n smpboot_thread_fn+0x24d/0x3b0\n kthread+0x3bd/0x410\n ret_from_fork+0x35/0x40\n ret_from_fork_asm+0x1a/0x30\n\nno locks held by irq_work/8/88.\nirq event stamp: 200272\nhardirqs last  enabled at (200272): [\u003cffffffffb0f56121\u003e] finish_task_switch+0x131/0x320\nhardirqs last disabled at (200271): [\u003cffffffffb25c7859\u003e] __schedule+0x129/0xd70\nsoftirqs last  enabled at (0): [\u003cffffffffb0ee093f\u003e] copy_process+0x4df/0x1cc0\nsoftirqs last disabled at (0): [\u003c0000000000000000\u003e] 0x0\n\n------------------------------------------------------------------------\n\nThe problem is that irq-work handlers run with interrupts enabled, which\nmeans that rcu_preempt_deferred_qs_handler() could be interrupted,\nand that interrupt handler might contain an RCU read-side critical\nsection, which might invoke rcu_read_unlock_special().  In the strict\nKCSAN mode of operation used by RCU, this constitutes a data race on\nthe -\u003edefer_qs_iw_pending field.\n\nThis commit therefore disables interrupts across the portion of the\nrcu_preempt_deferred_qs_handler() that updates the -\u003edefer_qs_iw_pending\nfield.  This suffices because this handler is not a fast path."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nrcu: Proteger -\u003edefer_qs_iw_pending de una condici\u00f3n de carrera de datos\n\nEn kernels compilados con CONFIG_IRQ_WORK=y, cuando se invoca rcu_read_unlock() dentro de una regi\u00f3n de c\u00f3digo con interrupciones deshabilitadas [1], invocar\u00e1 rcu_read_unlock_special(), que utiliza un gestor de trabajo de IRQ para forzar al sistema a notar cu\u00e1ndo termina realmente la secci\u00f3n cr\u00edtica del lado de lectura de RCU. Ese final no ocurrir\u00e1 hasta que las interrupciones est\u00e9n habilitadas, como muy pronto.\n\nEn algunos kernels, como los iniciados con rcutree.use_softirq=y, el gestor de trabajo de IRQ se utiliza incondicionalmente.\n\nEl campo -\u003edefer_qs_iw_pending de la estructura rcu_data por CPU es actualizado por el gestor de trabajo de IRQ y es tanto le\u00eddo como actualizado por rcu_read_unlock_special(). Esto result\u00f3 en el siguiente \u0027splat\u0027 de KCSAN:\n\n------------------------------------------------------------------------\n\nERROR: KCSAN: condici\u00f3n de carrera de datos en rcu_preempt_deferred_qs_handler / rcu_read_unlock_special\n\nlectura a 0xffff96b95f42d8d8 de 1 bytes por la tarea 90 en la CPU 8:\n rcu_read_unlock_special+0x175/0x260\n __rcu_read_unlock+0x92/0xa0\n rt_spin_unlock+0x9b/0xc0\n __local_bh_enable+0x10d/0x170\n __local_bh_enable_ip+0xfb/0x150\n rcu_do_batch+0x595/0xc40\n rcu_cpu_kthread+0x4e9/0x830\n smpboot_thread_fn+0x24d/0x3b0\n kthread+0x3bd/0x410\n ret_from_fork+0x35/0x40\n ret_from_fork_asm+0x1a/0x30\n\nescritura a 0xffff96b95f42d8d8 de 1 bytes por la tarea 88 en la CPU 8:\n rcu_preempt_deferred_qs_handler+0x1e/0x30\n irq_work_single+0xaf/0x160\n run_irq_workd+0x91/0xc0\n smpboot_thread_fn+0x24d/0x3b0\n kthread+0x3bd/0x410\n ret_from_fork+0x35/0x40\n ret_from_fork_asm+0x1a/0x30\n\nning\u00fan bloqueo mantenido por irq_work/8/88.\nmarca de tiempo de evento IRQ: 200272\nhardirqs habilitadas por \u00faltima vez en (200272): [\u003cffffffffb0f56121\u003e] finish_task_switch+0x131/0x320\nhardirqs deshabilitadas por \u00faltima vez en (200271): [\u003cffffffffb25c7859\u003e] __schedule+0x129/0xd70\nsoftirqs habilitadas por \u00faltima vez en (0): [\u003cffffffffb0ee093f\u003e] copy_process+0x4df/0x1cc0\nsoftirqs deshabilitadas por \u00faltima vez en (0): [\u003c0000000000000000\u003e] 0x0\n\n------------------------------------------------------------------------\n\nEl problema es que los gestores de trabajo de IRQ se ejecutan con las interrupciones habilitadas, lo que significa que rcu_preempt_deferred_qs_handler() podr\u00eda ser interrumpido, y ese gestor de interrupciones podr\u00eda contener una secci\u00f3n cr\u00edtica del lado de lectura de RCU, que podr\u00eda invocar rcu_read_unlock_special(). En el modo de operaci\u00f3n estricto de KCSAN utilizado por RCU, esto constituye una condici\u00f3n de carrera de datos en el campo -\u003edefer_qs_iw_pending.\n\nPor lo tanto, este \u0027commit\u0027 deshabilita las interrupciones a lo largo de la porci\u00f3n de rcu_preempt_deferred_qs_handler() que actualiza el campo -\u003edefer_qs_iw_pending. Esto es suficiente porque este gestor no es una ruta r\u00e1pida."
          }
        ],
        "id": "CVE-2025-39749",
        "lastModified": "2026-10-19T21:10:00.160",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.0,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.0,
              "impactScore": 5.9,
              "source": "nvd@nist.gov",
              "type": "Primary"
            }
          ]
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        "published": "2025-09-11T17:15:38.430",
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            "tags": [
              "Mailing List",
              "Third Party Advisory"
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            "url": "https://cert-portal.siemens.com/productcert/html/ssa-032379.html"
          }
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Modified",
        "weaknesses": [
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            "description": [
              {
                "lang": "en",
                "value": "NVD-CWE-noinfo"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
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    },
    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-06-30T10:23:25+00:00",
      "cve": "CVE-2025-39749",
      "id": "CVE-2025-39749",
      "initial_release_date": "2025-09-11T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: rcu: Protect -\u003edefer_qs_iw_pending from data race",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-39749.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-10-15T16:33:50Z",
      "cve": "CVE-2025-39749",
      "id": "CVE-2025-39749",
      "initial_release_date": "2025-09-11T23:24:20Z",
      "product_status:known_affected": "596",
      "product_status:known_not_affected": "187",
      "product_status:recommended": "495",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-39749",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2025/cve-2025-39749.json",
      "version": "46"
    }
  }
}



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