In the Linux kernel, the following vulnerability has been resolved: cgroup: Avoid iteration of...

{
  "credits": [],
  "cve_id": "CVE-2026-98163",
  "cvss": {
    "score": null,
    "vector_string": null
  },
  "cvss_severities": {
    "cvss_v3": {
      "score": 0.0,
      "vector_string": null
    },
    "cvss_v4": {
      "score": 0.0,
      "vector_string": null
    }
  },
  "cwes": [],
  "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)",
  "epss": {
    "percentage": 0.00177,
    "percentile": 0.0655
  },
  "ghsa_id": "GHSA-qwg6-2j4v-5xw5",
  "github_reviewed_at": null,
  "html_url": "https://github.com/advisories/GHSA-qwg6-2j4v-5xw5",
  "identifiers": [
    {
      "type": "GHSA",
      "value": "GHSA-qwg6-2j4v-5xw5"
    },
    {
      "type": "CVE",
      "value": "CVE-2026-98163"
    }
  ],
  "nvd_published_at": "2026-09-26T09:16:38Z",
  "published_at": "2026-09-26T09:30:20Z",
  "references": [
    "https://nvd.nist.gov/vuln/detail/CVE-2026-98163",
    "https://git.kernel.org/stable/c/057dac23d329d5c5ed62352f2659a39fd46c6d4a",
    "https://git.kernel.org/stable/c/828938118d6c2bb711301748c3e39e4bed6a62f5",
    "https://github.com/advisories/GHSA-qwg6-2j4v-5xw5"
  ],
  "repository_advisory_url": null,
  "severity": "unknown",
  "source_code_location": "",
  "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\ncgroup: Avoid iteration of...",
  "type": "unreviewed",
  "updated_at": "2026-09-26T09:30:26Z",
  "url": "https://api.github.com/advisories/GHSA-qwg6-2j4v-5xw5",
  "vulnerabilities": [],
  "withdrawn_at": null
}