{"id":"CVE-2026-93197","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nmemcg: move LRU size accounting on reparenting instead of copying it\n\nWhen a memory cgroup is offlined its LRU folios are reparented to the\nparent","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nmemcg: move LRU size accounting on reparenting instead of copying it\n\nWhen a memory cgroup is offlined its LRU folios are reparented to the\nparent.  lruvec_reparent_lru…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 07a6e9a2c199fed361f528781284d56771d0016f < 007bc1842317bb99f5f6205afede940f951674c2","Linux >= 07a6e9a2c199fed361f528781284d56771d0016f < 0e0ac326c511d514817cc7b6d7741afd59098ce2","Linux 7.1"],"published":"2026-09-17","updated":"2026-09-17","sourceUpdated":"2026-09-17T17:18:15.990","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-93197","references":[{"url":"https://git.kernel.org/stable/c/007bc1842317bb99f5f6205afede940f951674c2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/0e0ac326c511d514817cc7b6d7741afd59098ce2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd","cve.org"],"ingestedAt":"2026-09-17T16:21:47.722Z","epss":0.00198,"epssPercentile":0.08469,"slug":"CVE-2026-93197","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nmemcg: move LRU size accounting on reparenting instead of copying it\n\nWhen a memory cgroup is offlined its LRU folios are reparented to the\nparent.  lruvec_reparent_lru() splices the child's lists into the\nparent's and credits the parent with the child's per-zone\nlru_zone_size[], but never clears the child's copy, so the size is\ncopied rather than moved.  lru_gen_reparent_memcg() does the same for\nMGLRU.\n\nThe parent is left correct, credited with exactly the folios it took\nover.  The stale value sits on the child and nothing will correct it:\nfolio->memcg_data now resolves to the parent, so every later\nupdate_lru_size() for those folios goes there.\n\nDying cgroups are not freed immediately and mem_cgroup_iter() still\nwalks them, so shrink_lruvec() keeps being called on them.\nget_scan_count() reads the phantom counter through lruvec_lru_size() and\nthe scan loop then grinds through nr[] in SWAP_CLUSTER_MAX steps against\nan empty list, for as long as the dead cgroup lives.  Under MGLRU the\nMGLRU scanner runs instead, but count_shadow_nodes() sums all of\nNR_LRU_LISTS through lruvec_lru_size() and over-budgets the shadow node\nlimit just the same.\n\nOn one 251 GiB host a sweep of every mz->lru_zone_size[] found 380\ncounters describing folios on no list at all: 124777314 pages, 476 GiB,\n1.89x the machine's RAM, across 57 cgroups.  All were on memcgs with\nCSS_DYING set and CSS_ONLINE clear, and parent/child pairs reported\nbyte-identical sizes.\n\nLRU_UNEVICTABLE needs its size moved too.  Its list is deliberately not\nspliced because lruvec_init() poisons the head - the unevictable LRU is\nimaginary and folios are never threaded on it - but the size is kept by\nlruvec_add_folio()/lruvec_del_folio() and those folios account to the\nparent from here on.\n\nThis depends on commit bf4ade7dbd76 (\"memcg: keep folio's objcg same as\nits node\") and must not be backported ahead of it.  Without that\ninvariant a folio's objcg can belong to another node, so a folio already\nspliced onto the parent's list can still resolve to the child's lruvec\nuntil the objcg's node is reparented in a later iteration of\nmemcg_reparent_objcgs(); clearing the child's counter early then lets\nlruvec_del_folio() underflow it and trip the WARN_ONCE()/VM_BUG_ON() in\nmem_cgroup_update_lru_size().\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}