{"id":"CVE-2026-31586","revision":"6b5f7b22b4e44edf8e756ef257a45b77","records":[{"revision":"6b5f7b22b4e44edf8e756ef257a45b77","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-31586","aliases":[],"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 \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.","state":0,"publishedAt":"2026-04-24T14:42:14.937+00:00","modifiedAt":"2026-10-19T18:55:59.448+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"mm/backing-dev.c\"\n ],\n \"versions\": [\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"23acef4156c260e8598397a1a2e8b3a23e919893\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"1bd36e93b542d9dd020190c6607c6a3663405195\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"740ba1ebb223f137ff088ab74d533a13f9167bd8\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"115a5266749dcde7fe4127e8623d19c752088f69\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"dfc8292a1d6782c76b626315605e0585a5a18447\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"ea3af09eb87d8f8708c66747fcf1a2762902e839\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"50879a3c1faf06e661090015d59e2127255cff27\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"67cb119d32f35e32acd0393bbeb318b2bb1fdafe\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"59b57717fff8b562825d9d25e0180ad7e8048ca9\",\n \"lessThan\": \"8f5857be99f1ed1fa80991c72449541f634626ee\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"mm/backing-dev.c\"\n ],\n \"versions\": [\n {\n \"version\": \"4.19\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"4.19\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.10.258\",\n \"lessThanOrEqual\": \"5.10.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.209\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.175\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.136\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.83\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.24\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.19.14\",\n \"lessThanOrEqual\": \"6.19.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.0.1\",\n \"lessThanOrEqual\": \"7.0.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.1\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8,"severity":"HIGH"}],"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"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31586","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-31586","identifiers":["CVE-2026-31586"]},"retained":false,"historicalAffected":[]}],"coverage":[]}