FKIE_CVE-2026-31586

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-10-19 19:18
Severity
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last reference, the blkcg can be freed asynchronously (css_free_rwork_fn -> blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the pointer to access blkcg->online_pin, resulting in a use-after-free: BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531 Workqueue: cgwb_release cgwb_release_workfn Call Trace: <TASK> blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) cgwb_release_workfn (mm/backing-dev.c:629) process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385) Freed by task 1016: kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561) css_free_rwork_fn (kernel/cgroup/cgroup.c:5542) process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385) ** Stack based on commit 66672af7a095 ("Add linux-next specific files for 20260410") I am seeing this crash sporadically in Meta fleet across multiple kernel versions. A full reproducer is available at: https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh (The race window is narrow. To make it easily reproducible, inject a msleep(100) between css_put() and blkcg_unpin_online() in cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the reproducer triggers the splat reliably in less than a second.) Fix this by moving blkcg_unpin_online() before css_put(), so the cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online() accesses it.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafePatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626eePatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839Patch
0b142b55-0307-4c5a-b3c9-f314f3fb7c5ehttps://cert-portal.siemens.com/productcert/html/ssa-784472.html
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
To clipboard 

{
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          "vendor": "Siemens",
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  "configurations": [
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: blk-cgroup: fix use-after-free in cgwb_release_workfn()\n\ncgwb_release_workfn() calls css_put(wb-\u003eblkcg_css) and then later accesses\nwb-\u003eblkcg_css again via blkcg_unpin_online().  If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn -\u003e\nblkcg_css_free -\u003e kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg-\u003eonline_pin, resulting in a use-after-free:\n\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n  Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531\n   Workqueue: cgwb_release cgwb_release_workfn\n   Call Trace:\n    \u003cTASK\u003e\n     blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n     cgwb_release_workfn (mm/backing-dev.c:629)\n     process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)\n\n   Freed by task 1016:\n    kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)\n    css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)\n    process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)\n\n** Stack based on commit 66672af7a095 (\"Add linux-next specific files\nfor 20260410\")\n\nI am seeing this crash sporadically in Meta fleet across multiple kernel\nversions.  A full reproducer is available at:\nhttps://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh\n\n(The race window is narrow.  To make it easily reproducible, inject a\nmsleep(100) between css_put() and blkcg_unpin_online() in\ncgwb_release_workfn().  With that delay and a KASAN-enabled kernel, the\nreproducer triggers the splat reliably in less than a second.)\n\nFix this by moving blkcg_unpin_online() before css_put(), so the\ncgwb\u0027s CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it."
    }
  ],
  "id": "CVE-2026-31586",
  "lastModified": "2026-10-19T19:18:00.470",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-31586",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-10-16T15:10:59.894304Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-04-24T15:16:33.393",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
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      "url": "https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27"
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    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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    },
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
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    },
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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    },
    {
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      "tags": [
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    },
    {
      "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-784472.html"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    },
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary"
    }
  ]
}



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