{"id":"CVE-2026-98163","revision":null,"records":[{"revision":"c279784376de4218b4ed2ecfa0d8c3f6","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-98163","aliases":[],"title":"cgroup: Avoid iteration of dying tasks with zero refcount","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ncgroup: Avoid iteration of dying tasks with zero refcount\n\nThe commit 260fbcb92bbea (\"cgroup: Move dying_tasks cleanup from\ncgroup_task_release() to cgroup_task_free()\") extended the lifetime of\ntasks on the dying_tasks list.\nThe iterators have provision to go through dying_tasks because of\ndying threadgroup leaders or explicit CSS_TASK_ITER_WITH_DEAD, however,\nit was expected that such tasks can obtain a new reference (that is\npossible before cgroup_task_release()/put_task_struct_rcu_user()).\nThe tasks after cgroup_task_release() and before cgroup_task_free()\nare subject to race when they may or may not have ->usage count > 0.\n\nThe race window is between css_task_iter_next() invocations\nwhen css_set_lock is released and we may arrive at a new ->task_pos.\nThe iterator should not attempt to resurrect tasks whose ->usage count\ndropped to zero. (When that happens, __put_task_struct_rcu_cb() is\nalready imminent and the returned task_struct would could be used\nafter free.)\n\nAs for the fix, we cannot simply check the signal->live count of a task\non the dying list because that won't distinguish regular zombies waiting\nto be reaped from RCU remnant tasks that are going to be free'd.\nTherefore add an extra check to rule out ->usage==0 tasks from any\niteration.\n\nThe repeat: loop in css_task_iter_advance() doesn't consider ->usage\ncount, so add a new loop to css_task_iter_next() to skip de-used tasks\non the dying_list.\n\nRough illustration of the possible race\n\n R (reader of cgroup.procs) T (thread) L (group leader)\n --------------------------------- -------------------------------- --------------------------------\n L exits, signal->live > 0\n cgroup_task_dead(L)\n css_set_skip_task_iters() // skips only cset->tasks\n list_add_tail(&L->cg_list, &cset->dying_tasks)\n css_task_iter_next()\n take css_set_lock\n css_task_iter_advance()\n leader && signal->live != 0\n => it->task_pos = &L->cg_list\n release css_set_lock\n T exits\n --signal->live == 0\n\t\t\t\t cgroup_task_dead(T) // css_set_lock\n release_task(T)\n cgroup_task_release(T)\n release_task(L) // zap_leader\n cgroup_task_release(L)\n put_task_struct_rcu_user(L)\n ...RCU...\n put_task_struct(L)\n L->usage = 0\n /* L still on dying_tasks */\n ...RCU...\n __put_task_struct(L)\n css_task_iter_next() // another iteration\n take css_set_lock\n it->task_pos = &L->cg_list\n get_task_struct(L)\n => addition on 0\n drop css_set_lock\n cgroup_task_free(L)\n css_set_skip_task_iters() // dying skip comes too late\n free_task(L)\n cgroup_procs_show()\n task_pid_vnr(L)","state":0,"publishedAt":"2026-09-26T08:31:50.899+00:00","modifiedAt":"2026-10-19T09:14:56.823+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 \"kernel/cgroup/cgroup.c\"\n ],\n \"versions\": [\n {\n \"version\": \"260fbcb92bbeacfcd050410fdc2d24ab15044400\",\n \"lessThan\": \"828938118d6c2bb711301748c3e39e4bed6a62f5\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"260fbcb92bbeacfcd050410fdc2d24ab15044400\",\n \"lessThan\": \"057dac23d329d5c5ed62352f2659a39fd46c6d4a\",\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 \"kernel/cgroup/cgroup.c\"\n ],\n \"versions\": [\n {\n \"version\": \"6.19\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"6.19\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2.8\",\n \"lessThanOrEqual\": \"7.2.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.3\",\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/828938118d6c2bb711301748c3e39e4bed6a62f5","https://git.kernel.org/stable/c/057dac23d329d5c5ed62352f2659a39fd46c6d4a"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98163","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-98163","identifiers":["CVE-2026-98163"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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