{"id":"CVE-2026-31586","summary":"mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()","details":"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's CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it.","modified":"2026-06-18T03:56:31.892630357Z","published":"2026-04-24T14:42:14.937Z","related":["CGA-gjj8-83q2-r5c8","SUSE-SU-2026:2111-1","SUSE-SU-2026:21841-1","SUSE-SU-2026:21845-1","SUSE-SU-2026:21860-1","SUSE-SU-2026:21876-1","SUSE-SU-2026:21877-1","SUSE-SU-2026:21916-1","SUSE-SU-2026:21919-1","SUSE-SU-2026:2195-1","SUSE-SU-2026:2202-1","SUSE-SU-2026:2215-1","SUSE-SU-2026:2216-1","SUSE-SU-2026:2217-1","SUSE-SU-2026:2238-1","openSUSE-SU-2026:10703-1","openSUSE-SU-2026:20826-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31586.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69"},{"type":"WEB","url":"https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195"},{"type":"WEB","url":"https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893"},{"type":"WEB","url":"https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27"},{"type":"WEB","url":"https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe"},{"type":"WEB","url":"https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee"},{"type":"WEB","url":"https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31586.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31586"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"59b57717fff8b562825d9d25e0180ad7e8048ca9"},{"fixed":"23acef4156c260e8598397a1a2e8b3a23e919893"},{"fixed":"1bd36e93b542d9dd020190c6607c6a3663405195"},{"fixed":"740ba1ebb223f137ff088ab74d533a13f9167bd8"},{"fixed":"115a5266749dcde7fe4127e8623d19c752088f69"},{"fixed":"dfc8292a1d6782c76b626315605e0585a5a18447"},{"fixed":"ea3af09eb87d8f8708c66747fcf1a2762902e839"},{"fixed":"50879a3c1faf06e661090015d59e2127255cff27"},{"fixed":"67cb119d32f35e32acd0393bbeb318b2bb1fdafe"},{"fixed":"8f5857be99f1ed1fa80991c72449541f634626ee"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31586.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.19.0"},{"fixed":"5.10.258"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.209"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.175"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.136"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.83"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.24"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.14"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.20.0"},{"fixed":"7.0.1"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31586.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}