{"id":"CVE-2026-31586","title":"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_un…","summary":"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_un…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-416"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 4.19, < 6.6.136","linux_kernel >= 6.7, < 6.12.83","linux_kernel >= 6.13, < 6.18.24","linux_kernel >= 6.19, < 6.19.14","linux_kernel >= 7.0, < 7.0.1"],"patched":["linux_kernel 7.0.1"],"published":"2026-04-24","updated":"2026-10-15","sourceUpdated":"2026-10-15T02:19:12.053","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-31586","references":[{"url":"https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-784472.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00174,"epssPercentile":0.0641,"ingestedAt":"2026-10-15T03:30:12.858Z","slug":"CVE-2026-31586","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `linux_kernel >= 4.19, < 6.6.136`\n- `linux_kernel >= 6.7, < 6.12.83`\n- `linux_kernel >= 6.13, < 6.18.24`\n- `linux_kernel >= 6.19, < 6.19.14`\n- `linux_kernel >= 7.0, < 7.0.1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 7.0.1`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}