{"id":"CVE-2026-31586","state":"PUBLISHED","title":"mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()","description":"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->blkcg_css) and then later accesses\nwb->blkcg_css again via blkcg_unpin_online().  If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn ->\nblkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg->online_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    <TASK>\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's CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it.","publishedAt":"2026-04-24T14:42:14.937Z","updatedAt":"2026-10-19T18:55:59.448Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"23acef4156c260e8598397a1a2e8b3a23e919893","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"1bd36e93b542d9dd020190c6607c6a3663405195","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"740ba1ebb223f137ff088ab74d533a13f9167bd8","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"115a5266749dcde7fe4127e8623d19c752088f69","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"dfc8292a1d6782c76b626315605e0585a5a18447","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"ea3af09eb87d8f8708c66747fcf1a2762902e839","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"50879a3c1faf06e661090015d59e2127255cff27","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"67cb119d32f35e32acd0393bbeb318b2bb1fdafe","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"8f5857be99f1ed1fa80991c72449541f634626ee","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/backing-dev.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.19","versionType":"semver"},{"version":"5.10.258","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.209","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.175","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.136","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.83","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.24","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.14","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0.1","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/backing-dev.c"]}],"references":["https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893","https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195","https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8","https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69","https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447","https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839","https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27","https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe","https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31586.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31586","state":"PUBLISHED","datePublished":"2026-04-24T14:42:14.937Z","dateUpdated":"2026-10-19T18:55:59.448Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.120Z"},"containers":{"cna":{"title":"mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()","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->blkcg_css) and then later accesses\nwb->blkcg_css again via blkcg_unpin_online().  If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn ->\nblkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg->online_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    <TASK>\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's CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"23acef4156c260e8598397a1a2e8b3a23e919893","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"1bd36e93b542d9dd020190c6607c6a3663405195","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"740ba1ebb223f137ff088ab74d533a13f9167bd8","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"115a5266749dcde7fe4127e8623d19c752088f69","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"dfc8292a1d6782c76b626315605e0585a5a18447","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"ea3af09eb87d8f8708c66747fcf1a2762902e839","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"50879a3c1faf06e661090015d59e2127255cff27","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"67cb119d32f35e32acd0393bbeb318b2bb1fdafe","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","status":"affected","lessThan":"8f5857be99f1ed1fa80991c72449541f634626ee","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/backing-dev.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.19","versionType":"semver"},{"version":"5.10.258","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.209","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.175","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.136","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.83","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.24","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.14","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0.1","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/backing-dev.c"]}],"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"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","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’s 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."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:23:37.101Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.10.258"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.15.209"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.1.175"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.6.136"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.12.83"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.18.24"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.19.14"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"7.0.1"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"7.1"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"affected":[{"vendor":"Siemens","product":"SIMATIC S7-1500 TM MFP - GNU/Linux subsystem","defaultStatus":"unknown","versions":[{"version":"0","status":"affected","lessThan":"*","versionType":"custom"}]}],"references":[{"url":"https://cert-portal.siemens.com/productcert/html/ssa-784472.html"}],"providerMetadata":{"shortName":"siemens-SADP","orgId":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","dateUpdated":"2026-10-15T01:17:09.063Z"},"x_adpType":"supplier"},{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-31586","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:10:59.894304Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-416","lang":"en","type":"CWE","description":"CWE-416 Use After Free"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T18:55:59.448Z"}}]}}}