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CVE-2021-47491 (GCVE-0-2021-47491)

Vulnerability from cvelistv5 – Published: 2024-05-22 08:19 – Updated: 2026-05-11 13:55
VLAI
Title
mm: khugepaged: skip huge page collapse for special files
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: khugepaged: skip huge page collapse for special files The read-only THP for filesystems will collapse THP for files opened readonly and mapped with VM_EXEC. The intended usecase is to avoid TLB misses for large text segments. But it doesn't restrict the file types so a THP could be collapsed for a non-regular file, for example, block device, if it is opened readonly and mapped with EXEC permission. This may cause bugs, like [1] and [2]. This is definitely not the intended usecase, so just collapse THP for regular files in order to close the attack surface. [shy828301@gmail.com: fix vm_file check [3]]
Severity
No CVSS data available.
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-05-22 18:42 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 , < 6d67b2a73b8e3a079c355bab3c1aef7d85a044b8 (git)
Affected: 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 , < 5fcb6fce74ffa614d964667110cf1a516c48c6d9 (git)
Affected: 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 , < a4aeaa06d45e90f9b279f0b09de84bd00006e733 (git)
guessed Create a notification for this product.
Linux Linux Affected: 5.4
Unaffected: 0 , < 5.4 (semver)
Unaffected: 5.10.78 , ≤ 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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    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://git.kernel.org/stable/c/6d67b2a73b8e3a079c355bab3c1aef7d85a044b8\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/5fcb6fce74ffa614d964667110cf1a516c48c6d9\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/a4aeaa06d45e90f9b279f0b09de84bd00006e733\", \"tags\": [\"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T05:39:59.599Z\"}}, {\"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-47491\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2024-05-22T18:42:55.199651Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2024-05-22T18:43:01.766Z\"}, \"title\": \"CISA ADP Vulnrichment\"}], \"cna\": {\"title\": \"mm: khugepaged: skip huge page collapse for special files\", \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0\", \"lessThan\": \"6d67b2a73b8e3a079c355bab3c1aef7d85a044b8\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0\", \"lessThan\": \"5fcb6fce74ffa614d964667110cf1a516c48c6d9\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0\", \"lessThan\": \"a4aeaa06d45e90f9b279f0b09de84bd00006e733\", \"versionType\": \"git\"}], \"programFiles\": [\"mm/khugepaged.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.4\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.4\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.78\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.14.16\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.14.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"mm/khugepaged.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/6d67b2a73b8e3a079c355bab3c1aef7d85a044b8\"}, {\"url\": \"https://git.kernel.org/stable/c/5fcb6fce74ffa614d964667110cf1a516c48c6d9\"}, {\"url\": \"https://git.kernel.org/stable/c/a4aeaa06d45e90f9b279f0b09de84bd00006e733\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nmm: khugepaged: skip huge page collapse for special files\\n\\nThe read-only THP for filesystems will collapse THP for files opened\\nreadonly and mapped with VM_EXEC.  The intended usecase is to avoid TLB\\nmisses for large text segments.  But it doesn\u0027t restrict the file types\\nso a THP could be collapsed for a non-regular file, for example, block\\ndevice, if it is opened readonly and mapped with EXEC permission.  This\\nmay cause bugs, like [1] and [2].\\n\\nThis is definitely not the intended usecase, so just collapse THP for\\nregular files in order to close the attack surface.\\n\\n[shy828301@gmail.com: fix vm_file check [3]]\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.78\", \"versionStartIncluding\": \"5.4\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.14.16\", \"versionStartIncluding\": \"5.4\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15\", \"versionStartIncluding\": \"5.4\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2025-05-04T07:12:11.704Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-47491\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2025-05-04T07:12:11.704Z\", \"dateReserved\": \"2024-05-22T06:20:56.201Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-05-22T08:19:40.101Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.1"
    }
  }
}



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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.


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.