CVE-2026-98163 (GCVE-0-2026-98163)

Vulnerability from cvelistv5 – Published: 2026-09-26 08:31 – Updated: 2026-09-26 08:31
VLAI
Title
cgroup: Avoid iteration of dying tasks with zero refcount
Summary
In the Linux kernel, the following vulnerability has been resolved: cgroup: Avoid iteration of dying tasks with zero refcount The commit 260fbcb92bbea ("cgroup: Move dying_tasks cleanup from cgroup_task_release() to cgroup_task_free()") extended the lifetime of tasks on the dying_tasks list. The iterators have provision to go through dying_tasks because of dying threadgroup leaders or explicit CSS_TASK_ITER_WITH_DEAD, however, it was expected that such tasks can obtain a new reference (that is possible before cgroup_task_release()/put_task_struct_rcu_user()). The tasks after cgroup_task_release() and before cgroup_task_free() are subject to race when they may or may not have ->usage count > 0. The race window is between css_task_iter_next() invocations when css_set_lock is released and we may arrive at a new ->task_pos. The iterator should not attempt to resurrect tasks whose ->usage count dropped to zero. (When that happens, __put_task_struct_rcu_cb() is already imminent and the returned task_struct would could be used after free.) As for the fix, we cannot simply check the signal->live count of a task on the dying list because that won't distinguish regular zombies waiting to be reaped from RCU remnant tasks that are going to be free'd. Therefore add an extra check to rule out ->usage==0 tasks from any iteration. The repeat: loop in css_task_iter_advance() doesn't consider ->usage count, so add a new loop to css_task_iter_next() to skip de-used tasks on the dying_list. Rough illustration of the possible race R (reader of cgroup.procs) T (thread) L (group leader) --------------------------------- -------------------------------- -------------------------------- L exits, signal->live > 0 cgroup_task_dead(L) css_set_skip_task_iters() // skips only cset->tasks list_add_tail(&L->cg_list, &cset->dying_tasks) css_task_iter_next() take css_set_lock css_task_iter_advance() leader && signal->live != 0 => it->task_pos = &L->cg_list release css_set_lock T exits --signal->live == 0 cgroup_task_dead(T) // css_set_lock release_task(T) cgroup_task_release(T) release_task(L) // zap_leader cgroup_task_release(L) put_task_struct_rcu_user(L) ...RCU... put_task_struct(L) L->usage = 0 /* L still on dying_tasks */ ...RCU... __put_task_struct(L) css_task_iter_next() // another iteration take css_set_lock it->task_pos = &L->cg_list get_task_struct(L) => addition on 0 drop css_set_lock cgroup_task_free(L) css_set_skip_task_iters() // dying skip comes too late free_task(L) cgroup_procs_show() task_pid_vnr(L)
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 260fbcb92bbeacfcd050410fdc2d24ab15044400 , < 828938118d6c2bb711301748c3e39e4bed6a62f5 (git)
Affected: 260fbcb92bbeacfcd050410fdc2d24ab15044400 , < 057dac23d329d5c5ed62352f2659a39fd46c6d4a (git)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.2.8 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc4 , ≤ * (original_commit_for_fix)
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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/cgroup/cgroup.c"
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.19",
                  "vulnerable": true
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          "value": "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 -\u003eusage count \u003e 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 -\u003etask_pos.\nThe iterator should not attempt to resurrect tasks whose -\u003eusage 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-\u003elive count of a task\non the dying list because that won\u0027t distinguish regular zombies waiting\nto be reaped from RCU remnant tasks that are going to be free\u0027d.\nTherefore add an extra check to rule out -\u003eusage==0 tasks from any\niteration.\n\nThe repeat: loop in css_task_iter_advance() doesn\u0027t consider -\u003eusage\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-\u003elive \u003e 0\n                                                                      cgroup_task_dead(L)\n                                                                        css_set_skip_task_iters() // skips only cset-\u003etasks\n                                                                        list_add_tail(\u0026L-\u003ecg_list, \u0026cset-\u003edying_tasks)\n  css_task_iter_next()\n    take css_set_lock\n    css_task_iter_advance()\n      leader \u0026\u0026 signal-\u003elive != 0\n      =\u003e it-\u003etask_pos = \u0026L-\u003ecg_list\n    release css_set_lock\n                                     T exits\n                                     --signal-\u003elive == 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-\u003eusage = 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-\u003etask_pos = \u0026L-\u003ecg_list\n    get_task_struct(L)\n      =\u003e 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)"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-26T08:31:50.899Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/828938118d6c2bb711301748c3e39e4bed6a62f5"
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        {
          "url": "https://git.kernel.org/stable/c/057dac23d329d5c5ed62352f2659a39fd46c6d4a"
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      "title": "cgroup: Avoid iteration of dying tasks with zero refcount",
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98163",
    "datePublished": "2026-09-26T08:31:50.899Z",
    "dateReserved": "2026-09-25T10:25:14.321Z",
    "dateUpdated": "2026-09-26T08:31:50.899Z",
    "state": "PUBLISHED"
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    "epss": {
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      "date": "2026-09-27",
      "epss": "0.00177",
      "percentile": "0.06543"
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
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                    "versionType": "semver"
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        "descriptions": [
          {
            "lang": "en",
            "value": "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 -\u003eusage count \u003e 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 -\u003etask_pos.\nThe iterator should not attempt to resurrect tasks whose -\u003eusage 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-\u003elive count of a task\non the dying list because that won\u0027t distinguish regular zombies waiting\nto be reaped from RCU remnant tasks that are going to be free\u0027d.\nTherefore add an extra check to rule out -\u003eusage==0 tasks from any\niteration.\n\nThe repeat: loop in css_task_iter_advance() doesn\u0027t consider -\u003eusage\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-\u003elive \u003e 0\n                                                                      cgroup_task_dead(L)\n                                                                        css_set_skip_task_iters() // skips only cset-\u003etasks\n                                                                        list_add_tail(\u0026L-\u003ecg_list, \u0026cset-\u003edying_tasks)\n  css_task_iter_next()\n    take css_set_lock\n    css_task_iter_advance()\n      leader \u0026\u0026 signal-\u003elive != 0\n      =\u003e it-\u003etask_pos = \u0026L-\u003ecg_list\n    release css_set_lock\n                                     T exits\n                                     --signal-\u003elive == 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-\u003eusage = 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-\u003etask_pos = \u0026L-\u003ecg_list\n    get_task_struct(L)\n      =\u003e 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)"
          }
        ],
        "id": "CVE-2026-98163",
        "lastModified": "2026-09-26T09:16:38.303",
        "metrics": {},
        "published": "2026-09-26T09:16:38.303",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/057dac23d329d5c5ed62352f2659a39fd46c6d4a"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/828938118d6c2bb711301748c3e39e4bed6a62f5"
          }
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "suse_vex": {
      "aggregate_severity": "not set",
      "current_release_date": "2026-09-26T16:21:48Z",
      "cve": "CVE-2026-98163",
      "id": "CVE-2026-98163",
      "initial_release_date": "2026-09-26T16:21:48Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-98163",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-98163.json",
      "version": "2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.