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CVE-2021-47506 (GCVE-0-2021-47506)

Vulnerability from cvelistv5 – Published: 2024-05-24 15:01 – Updated: 2026-08-05 08:48
VLAI
Title
nfsd: fix use-after-free due to delegation race
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix use-after-free due to delegation race A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru. Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread. I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-05-29 17:04 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < 04a8d07f3d58308b92630045560799a3faa3ebce (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < 348714018139c39533c55661a0c7c990671396b4 (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < 33645d3e22720cac1e4548f8fef57bf0649536ee (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < 2becaa990b93cbd2928292c0b669d3abb6cf06d4 (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < e0759696de6851d7536efddfdd2dfed4c4df1f09 (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < eeb0711801f5e19ef654371b627682aed3b11373 (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < 148c816f10fd11df27ca6a9b3238cdd42fa72cd3 (git)
Affected: dff1399f8addf7129c49bb2227469da79cc30b47 , < 548ec0805c399c65ed66c6641be467f717833ab5 (git)
guessed Create a notification for this product.
Linux Linux Affected: 3.17
Unaffected: 0 , < 3.17 (semver)
Unaffected: 4.4.296 , ≤ 4.4.* (semver)
Unaffected: 4.9.294 , ≤ 4.9.* (semver)
Unaffected: 4.14.259 , ≤ 4.14.* (semver)
Unaffected: 4.19.222 , ≤ 4.19.* (semver)
Unaffected: 5.4.168 , ≤ 5.4.* (semver)
Unaffected: 5.10.85 , ≤ 5.10.* (semver)
Unaffected: 5.15.8 , ≤ 5.15.* (semver)
Unaffected: 5.16 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix use-after-free due to delegation race\n\nA delegation break could arrive as soon as we\u0027ve called vfs_setlease.  A\ndelegation break runs a callback which immediately (in\nnfsd4_cb_recall_prepare) adds the delegation to del_recall_lru.  If we\nthen exit nfs4_set_delegation without hashing the delegation, it will be\nfreed as soon as the callback is done with it, without ever being\nremoved from del_recall_lru.\n\nSymptoms show up later as use-after-free or list corruption warnings,\nusually in the laundromat thread.\n\nI suspect aba2072f4523 \"nfsd: grant read delegations to clients holding\nwrites\" made this bug easier to hit, but I looked as far back as v3.0\nand it looks to me it already had the same problem.  So I\u0027m not sure\nwhere the bug was introduced; it may have been there from the beginning."
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            "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: nfsd: corrige el use-after-free debido a la ejecuci\u00f3n de delegaci\u00f3n. Una interrupci\u00f3n de la delegaci\u00f3n podr\u00eda llegar tan pronto como hayamos llamado a vfs_setlease. Una interrupci\u00f3n de la delegaci\u00f3n ejecuta una devoluci\u00f3n de llamada que inmediatamente (en nfsd4_cb_recall_prepare) agrega la delegaci\u00f3n a del_recall_lru. Si luego salimos de nfs4_set_delegation sin aplicar hash a la delegaci\u00f3n, se liberar\u00e1 tan pronto como finalice la devoluci\u00f3n de llamada, sin eliminarse nunca de del_recall_lru. Los s\u00edntomas aparecen m\u00e1s tarde como advertencias de use-after-free o de corrupci\u00f3n en la lista, generalmente en el hilo de la lavander\u00eda. Sospecho que aba2072f4523 \"nfsd: otorgar delegaciones de lectura a clientes que tienen escrituras\" hizo que este error fuera m\u00e1s f\u00e1cil de corregir, pero mir\u00e9 hasta la versi\u00f3n 3.0 y me parece que ya ten\u00eda el mismo problema. Entonces no estoy seguro de d\u00f3nde se introdujo el error; puede que haya estado ah\u00ed desde el principio."
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      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-47506.json",
      "version": "3"
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      "initial_release_date": "2024-05-28T03:32:52Z",
      "product_status:known_affected": "370",
      "product_status:known_not_affected": "101",
      "product_status:recommended": "691",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-47506",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-47506.json",
      "version": "67"
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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

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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.