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CVE-2021-47493 (GCVE-0-2021-47493)

Vulnerability from cvelistv5 – Published: 2024-05-22 08:19 – Updated: 2026-08-05 08:48
VLAI
Title
ocfs2: fix race between searching chunks and release journal_head from buffer_head
Summary
In the Linux kernel, the following vulnerability has been resolved: ocfs2: fix race between searching chunks and release journal_head from buffer_head Encountered a race between ocfs2_test_bg_bit_allocatable() and jbd2_journal_put_journal_head() resulting in the below vmcore. PID: 106879 TASK: ffff880244ba9c00 CPU: 2 COMMAND: "loop3" Call trace: panic oops_end no_context __bad_area_nosemaphore bad_area_nosemaphore __do_page_fault do_page_fault page_fault [exception RIP: ocfs2_block_group_find_clear_bits+316] ocfs2_block_group_find_clear_bits [ocfs2] ocfs2_cluster_group_search [ocfs2] ocfs2_search_chain [ocfs2] ocfs2_claim_suballoc_bits [ocfs2] __ocfs2_claim_clusters [ocfs2] ocfs2_claim_clusters [ocfs2] ocfs2_local_alloc_slide_window [ocfs2] ocfs2_reserve_local_alloc_bits [ocfs2] ocfs2_reserve_clusters_with_limit [ocfs2] ocfs2_reserve_clusters [ocfs2] ocfs2_lock_refcount_allocators [ocfs2] ocfs2_make_clusters_writable [ocfs2] ocfs2_replace_cow [ocfs2] ocfs2_refcount_cow [ocfs2] ocfs2_file_write_iter [ocfs2] lo_rw_aio loop_queue_work kthread_worker_fn kthread ret_from_fork When ocfs2_test_bg_bit_allocatable() called bh2jh(bg_bh), the bg_bh->b_private NULL as jbd2_journal_put_journal_head() raced and released the jounal head from the buffer head. Needed to take bit lock for the bit 'BH_JournalHead' to fix this race.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-06-06 18:35 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: ccd979bdbce9fba8412beb3f1de68a9d0171b12c , < 5043fbd294f5909a080ade0f04b70a4da9e122b7 (git)
Affected: ccd979bdbce9fba8412beb3f1de68a9d0171b12c , < 2e382600e8856ea654677b5134ee66e03ea72bc2 (git)
Affected: ccd979bdbce9fba8412beb3f1de68a9d0171b12c , < 6f1b228529ae49b0f85ab89bcdb6c365df401558 (git)
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Linux Linux Affected: 2.6.16
Unaffected: 0 , < 2.6.16 (semver)
Unaffected: 5.10.77 , ≤ 5.10.* (semver)
Unaffected: 5.14.16 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: fix race between searching chunks and release journal_head from buffer_head\n\nEncountered a race between ocfs2_test_bg_bit_allocatable() and\njbd2_journal_put_journal_head() resulting in the below vmcore.\n\n  PID: 106879  TASK: ffff880244ba9c00  CPU: 2   COMMAND: \"loop3\"\n  Call trace:\n    panic\n    oops_end\n    no_context\n    __bad_area_nosemaphore\n    bad_area_nosemaphore\n    __do_page_fault\n    do_page_fault\n    page_fault\n      [exception RIP: ocfs2_block_group_find_clear_bits+316]\n    ocfs2_block_group_find_clear_bits [ocfs2]\n    ocfs2_cluster_group_search [ocfs2]\n    ocfs2_search_chain [ocfs2]\n    ocfs2_claim_suballoc_bits [ocfs2]\n    __ocfs2_claim_clusters [ocfs2]\n    ocfs2_claim_clusters [ocfs2]\n    ocfs2_local_alloc_slide_window [ocfs2]\n    ocfs2_reserve_local_alloc_bits [ocfs2]\n    ocfs2_reserve_clusters_with_limit [ocfs2]\n    ocfs2_reserve_clusters [ocfs2]\n    ocfs2_lock_refcount_allocators [ocfs2]\n    ocfs2_make_clusters_writable [ocfs2]\n    ocfs2_replace_cow [ocfs2]\n    ocfs2_refcount_cow [ocfs2]\n    ocfs2_file_write_iter [ocfs2]\n    lo_rw_aio\n    loop_queue_work\n    kthread_worker_fn\n    kthread\n    ret_from_fork\n\nWhen ocfs2_test_bg_bit_allocatable() called bh2jh(bg_bh), the\nbg_bh-\u003eb_private NULL as jbd2_journal_put_journal_head() raced and\nreleased the jounal head from the buffer head.  Needed to take bit lock\nfor the bit \u0027BH_JournalHead\u0027 to fix this race."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: ocfs2: corrige la ejecuci\u00f3n entre fragmentos de b\u00fasqueda y libera journal_head de buffer_head Se encontr\u00f3 una ejecuci\u00f3n entre ocfs2_test_bg_bit_allocatable() y jbd2_journal_put_journal_head() que result\u00f3 en el siguiente vmcore. PID: 106879 TAREA: ffff880244ba9c00 CPU: 2 COMANDO: \"loop3\" Rastreo de llamadas: p\u00e1nico oops_end no_context __bad_area_nosemaphore bad_area_nosemaphore __do_page_fault do_page_fault page_fault [excepci\u00f3n RIP: ocfs2_block_group_find_clear_bits+316] 2_block_group_find_clear_bits [ocfs2] ocfs2_cluster_group_search [ocfs2] ocfs2_search_chain [ocfs2] ocfs2_claim_suballoc_bits [ocfs2] __ocfs2_claim_clusters [ocfs2] ocfs2_claim_clusters [ocfs2] ocfs2_local_alloc_slide_window [ocfs2] ocfs2_reserve_local_alloc_bits [ocfs2] ocfs2_reserve_clusters_with_limit [ocfs2] ocfs2_reserve_clusters [ocfs2] ocfs2_lock_refcount_allocators [ocfs2] 2_make_clusters_writable [ocfs2] ocfs2_replace_cow [ocfs2] ocfs2_refcount_cow [ocfs2] ocfs2_file_write_iter [ocfs2] lo_rw_aio loop_queue_work kthread_worker_fn kthread ret_from_fork Cuando ocfs2_test_bg_bit_allocatable () llamado bh2jh(bg_bh), el bg_bh-\u0026gt;b_private NULL como jbd2_journal_put_journal_head() corri\u00f3 y liber\u00f3 el encabezado del diario del encabezado del b\u00fafer. Era necesario bloquear el bit \u0027BH_JournalHead\u0027 para solucionar esta ejecuci\u00f3n."
          }
        ],
        "id": "CVE-2021-47493",
        "lastModified": "2026-08-04T10:17:05.613",
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                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
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                "baseSeverity": "MEDIUM",
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                "integrityImpact": "NONE",
                "privilegesRequired": "LOW",
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                "userInteraction": "NONE",
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                "version": "3.1"
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              "exploitabilityScore": 1.0,
              "impactScore": 3.6,
              "source": "nvd@nist.gov",
              "type": "Primary"
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                "options": [
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                "timestamp": "2024-06-06T18:35:17.607326Z",
                "version": "2.0.3"
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        "published": "2024-05-22T09:15:11.100",
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Modified",
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            "type": "Primary"
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      "current_release_date": "2026-08-04T19:56:36+00:00",
      "cve": "CVE-2021-47493",
      "id": "CVE-2021-47493",
      "initial_release_date": "2021-01-01T00:00:00+00:00",
      "product_status:known_not_affected": "198",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ocfs2: fix race between searching chunks and release journal_head from buffer_head",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-47493.json",
      "version": "3"
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    "suse_vex": {
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      "current_release_date": "2026-09-13T23:55:35Z",
      "cve": "CVE-2021-47493",
      "id": "CVE-2021-47493",
      "initial_release_date": "2024-05-28T15:29:59Z",
      "product_status:known_affected": "269",
      "product_status:known_not_affected": "224",
      "product_status:recommended": "543",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-47493",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-47493.json",
      "version": "57"
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    "vulnrichment": {
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              "dateUpdated": "2024-08-04T05:39:59.750Z",
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            ],
            "title": "CVE Program Container"
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          {
            "metrics": [
              {
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                  "content": {
                    "id": "CVE-2021-47493",
                    "options": [
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                      },
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                    "role": "CISA Coordinator",
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              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
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              "product": "Linux",
              "programFiles": [
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              "versions": [
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                    },
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              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: fix race between searching chunks and release journal_head from buffer_head\n\nEncountered a race between ocfs2_test_bg_bit_allocatable() and\njbd2_journal_put_journal_head() resulting in the below vmcore.\n\n  PID: 106879  TASK: ffff880244ba9c00  CPU: 2   COMMAND: \"loop3\"\n  Call trace:\n    panic\n    oops_end\n    no_context\n    __bad_area_nosemaphore\n    bad_area_nosemaphore\n    __do_page_fault\n    do_page_fault\n    page_fault\n      [exception RIP: ocfs2_block_group_find_clear_bits+316]\n    ocfs2_block_group_find_clear_bits [ocfs2]\n    ocfs2_cluster_group_search [ocfs2]\n    ocfs2_search_chain [ocfs2]\n    ocfs2_claim_suballoc_bits [ocfs2]\n    __ocfs2_claim_clusters [ocfs2]\n    ocfs2_claim_clusters [ocfs2]\n    ocfs2_local_alloc_slide_window [ocfs2]\n    ocfs2_reserve_local_alloc_bits [ocfs2]\n    ocfs2_reserve_clusters_with_limit [ocfs2]\n    ocfs2_reserve_clusters [ocfs2]\n    ocfs2_lock_refcount_allocators [ocfs2]\n    ocfs2_make_clusters_writable [ocfs2]\n    ocfs2_replace_cow [ocfs2]\n    ocfs2_refcount_cow [ocfs2]\n    ocfs2_file_write_iter [ocfs2]\n    lo_rw_aio\n    loop_queue_work\n    kthread_worker_fn\n    kthread\n    ret_from_fork\n\nWhen ocfs2_test_bg_bit_allocatable() called bh2jh(bg_bh), the\nbg_bh-\u003eb_private NULL as jbd2_journal_put_journal_head() raced and\nreleased the jounal head from the buffer head.  Needed to take bit lock\nfor the bit \u0027BH_JournalHead\u0027 to fix this race."
            }
          ],
          "metrics": [
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                "baseSeverity": "HIGH",
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                "version": "3.1"
              },
              "scenarios": [
                {
                  "lang": "en",
                  "value": "AV:L - The vulnerable path is reached via local filesystem operations (write/create \u2192 ocfs2_file_write_iter / namei \u2192 ocfs2_reserve_clusters \u2192 ocfs2_block_group_find_clear_bits \u2192 ocfs2_test_bg_bit_allocatable) on a mounted OCFS2 volume, not via network packet processing or physical device attachment.\nAC:L - An unprivileged attacker can drive both sides of the race by running concurrent writers/creators that trigger cluster bitmap searches while forcing journal commits (sync/fsync and heavy metadata activity), so winning the unprotected bh2jh window is attacker-controlled and retryable.\nPR:L - Once OCFS2 is mounted (typical shared-cluster deployment), any unprivileged local user with write permission to files or directories can exercise the allocation path; no CAP_SYS_ADMIN or init-namespace root is required along the vulnerable code path.\nUI:N - The attacker performs the concurrent writes and syncs themselves; no separate victim action such as opening a crafted file or confirming a prompt is required beyond the filesystem already being mounted.\nS:U - Impact is kernel memory corruption / oops within the same host OS authority (OCFS2/JBD2), with no VM escape, IOMMU bypass, or other cross-boundary scope change.\nC:H - Between bh2jh() and use of the journal_head, jbd2 can free the object, creating a use-after-free; per guidance a UAF enables heap reclaim and arbitrary kernel read primitives.\nI:H - The same journal_head UAF (spin_lock and access to b_committed_data on a freed slab object) is exploitable via heap spray for write and control-flow hijacking primitives in the kernel.\nA:H - The observed race already causes a kernel page-fault panic (NULL or dangling journal_head dereference in ocfs2_block_group_find_clear_bits), which is full availability impact even without a complete exploit."
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        "cveId": "CVE-2021-47493",
        "datePublished": "2024-05-22T08:19:41.419Z",
        "dateReserved": "2024-05-22T06:20:56.201Z",
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}



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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.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


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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.