CVE-2026-31586 (GCVE-0-2026-31586)

Vulnerability from cvelistv5 – Published: 2026-04-24 14:42 – Updated: 2026-04-24 14:42
VLAI?
Title
mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()
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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < dfc8292a1d6782c76b626315605e0585a5a18447 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < ea3af09eb87d8f8708c66747fcf1a2762902e839 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 50879a3c1faf06e661090015d59e2127255cff27 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 67cb119d32f35e32acd0393bbeb318b2bb1fdafe (git)
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    Linux Linux Unaffected: 6.12.83 , ≤ 6.12.* (semver)
Unaffected: 6.18.24 , ≤ 6.18.* (semver)
Unaffected: 6.19.14 , ≤ 6.19.* (semver)
Unaffected: 7.0.1 , ≤ 7.0.* (semver)
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          "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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-24T14:42:14.937Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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        {
          "url": "https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447"
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          "url": "https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839"
        },
        {
          "url": "https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27"
        },
        {
          "url": "https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe"
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      ],
      "title": "mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()",
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        "engine": "bippy-1.2.0"
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    "datePublished": "2026-04-24T14:42:14.937Z",
    "dateReserved": "2026-03-09T15:48:24.120Z",
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      "date": "2026-04-26",
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    "nvd": "{\"cve\":{\"id\":\"CVE-2026-31586\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-04-24T15:16:33.393\",\"lastModified\":\"2026-04-24T17:51:40.810\",\"vulnStatus\":\"Awaiting Analysis\",\"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.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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