CVE-2026-93197

{
  "id": "CVE-2026-93197",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-09-17T17:18:15.990",
  "lastModified": "2026-10-19T10:17:10.377",
  "vulnStatus": "Received",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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() 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()."
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "mm/folio.c",
            "mm/vmscan.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "07a6e9a2c199fed361f528781284d56771d0016f",
              "lessThan": "007bc1842317bb99f5f6205afede940f951674c2",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "07a6e9a2c199fed361f528781284d56771d0016f",
              "lessThan": "0e0ac326c511d514817cc7b6d7741afd59098ce2",
              "versionType": "git",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "programFiles": [
            "mm/folio.c",
            "mm/vmscan.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "7.1",
              "status": "affected"
            },
            {
              "version": "0",
              "lessThan": "7.1",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.2.6",
              "lessThanOrEqual": "7.2.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.3",
              "lessThanOrEqual": "*",
              "versionType": "original_commit_for_fix",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {},
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/007bc1842317bb99f5f6205afede940f951674c2",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/0e0ac326c511d514817cc7b6d7741afd59098ce2",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ]
}