CVE-2026-31586 (GCVE-0-2026-31586)
Vulnerability from cvelistv5
Published
2026-04-24 14:42
Modified
2026-10-19 18:55
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
Impacted products
Vendor Product Version
Linux Linux Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
Version: 59b57717fff8b562825d9d25e0180ad7e8048ca9
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          "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."
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              "value": "AV:L - The vulnerable path is reached by local cgroup/writeback activity: creating/removing cgroup v2 subgroups, moving a task into them, and dirtying files on a block-backed filesystem. There is no network or physical packet/device entry point.\nAC:L - Although the timing window is narrow, the attacker can repeatedly drive both cgroup teardown and cgwb creation/release through cgroup churn and buffered writes. Per the scoring rule for attacker-driven races and UAFs, this is low complexity.\nPR:L - The attacker needs local ability to manipulate a delegated cgroup subtree and run file I/O, which is available to low-privileged users in reasonable delegated cgroup v2 or container/user-slice deployments. It does not require real init-namespace root in those scenarios.\nUI:N - No victim action is required once the attacker has local execution and cgroup access. The attacker triggers creation, writeback, and removal directly.\nS:U - The vulnerability is in the host kernel\u2019s cgroup/writeback lifetime management and impacts the same kernel security authority. Standard local kernel privilege escalation is scored as unchanged scope.\nC:H - The bug is a use-after-free of a freed blkcg object after css_put can lead to blkcg_css_free and kfree before blkcg_unpin_online dereferences it. Kernel UAFs are scored high for confidentiality because reclaimed slab contents can be abused for memory disclosure primitives.\nI:H - The immediate UAF performs a refcount decrement/write through freed memory, and reclaimed-object corruption can plausibly be shaped into broader kernel heap corruption or control-flow compromise. Kernel UAF memory corruption is scored high for integrity.\nA:H - The reported failure is a slab-use-after-free in a kernel worker and can cause an oops, panic, or persistent kernel instability. Repeated local triggering makes availability impact high."
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    "dateUpdated": "2026-10-19T18:55:59.448Z",
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There is no network or physical packet/device entry point.\\nAC:L - Although the timing window is narrow, the attacker can repeatedly drive both cgroup teardown and cgwb creation/release through cgroup churn and buffered writes. Per the scoring rule for attacker-driven races and UAFs, this is low complexity.\\nPR:L - The attacker needs local ability to manipulate a delegated cgroup subtree and run file I/O, which is available to low-privileged users in reasonable delegated cgroup v2 or container/user-slice deployments. It does not require real init-namespace root in those scenarios.\\nUI:N - No victim action is required once the attacker has local execution and cgroup access. The attacker triggers creation, writeback, and removal directly.\\nS:U - The vulnerability is in the host kernel\\u2019s cgroup/writeback lifetime management and impacts the same kernel security authority. Standard local kernel privilege escalation is scored as unchanged scope.\\nC:H - The bug is a use-after-free of a freed blkcg object after css_put can lead to blkcg_css_free and kfree before blkcg_unpin_online dereferences it. Kernel UAFs are scored high for confidentiality because reclaimed slab contents can be abused for memory disclosure primitives.\\nI:H - The immediate UAF performs a refcount decrement/write through freed memory, and reclaimed-object corruption can plausibly be shaped into broader kernel heap corruption or control-flow compromise. Kernel UAF memory corruption is scored high for integrity.\\nA:H - The reported failure is a slab-use-after-free in a kernel worker and can cause an oops, panic, or persistent kernel instability. Repeated local triggering makes availability impact high.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"23acef4156c260e8598397a1a2e8b3a23e919893\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"1bd36e93b542d9dd020190c6607c6a3663405195\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"740ba1ebb223f137ff088ab74d533a13f9167bd8\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"115a5266749dcde7fe4127e8623d19c752088f69\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"dfc8292a1d6782c76b626315605e0585a5a18447\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"ea3af09eb87d8f8708c66747fcf1a2762902e839\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"50879a3c1faf06e661090015d59e2127255cff27\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"67cb119d32f35e32acd0393bbeb318b2bb1fdafe\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\", \"lessThan\": \"8f5857be99f1ed1fa80991c72449541f634626ee\", \"versionType\": \"git\"}], \"programFiles\": [\"mm/backing-dev.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.19\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.19\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.258\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.209\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.175\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.136\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.83\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.18.24\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.18.*\"}, {\"status\": \"unaffected\", \"version\": \"6.19.14\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.19.*\"}, {\"status\": \"unaffected\", \"version\": \"7.0.1\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"7.0.*\"}, {\"status\": \"unaffected\", \"version\": \"7.1\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"mm/backing-dev.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893\"}, {\"url\": \"https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195\"}, {\"url\": \"https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8\"}, {\"url\": \"https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69\"}, {\"url\": \"https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447\"}, {\"url\": \"https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839\"}, {\"url\": \"https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27\"}, {\"url\": \"https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe\"}, {\"url\": \"https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"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.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.258\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.209\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.175\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.136\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.83\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.18.24\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.19.14\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.0.1\", \"versionStartIncluding\": \"4.19\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.1\", \"versionStartIncluding\": \"4.19\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T12:23:37.101Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-31586\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-19T18:55:59.448Z\", \"dateReserved\": \"2026-03-09T15:48:24.120Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2026-04-24T14:42:14.937Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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