{
  "schemaVersion": 1,
  "attribution": [
    {
      "source": "CISA Known Exploited Vulnerabilities",
      "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog",
      "licence": "US government work"
    },
    {
      "source": "GitHub Advisory Database",
      "url": "https://github.com/advisories",
      "licence": "CC BY 4.0"
    },
    {
      "source": "Have I Been Pwned",
      "url": "https://haveibeenpwned.com/",
      "licence": "CC BY 4.0"
    },
    {
      "source": "CVE Program (CVE records)",
      "url": "https://www.cve.org/Legal/TermsOfUse",
      "licence": "CVE Terms of Use",
      "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.",
      "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy."
    },
    {
      "source": "FIRST EPSS",
      "url": "https://www.first.org/epss/",
      "licence": "free to use; FIRST requests attribution"
    }
  ],
  "record": {
    "id": "CVE-2021-46921",
    "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2021-46921",
    "idYear": 2021,
    "status": "PUBLISHED",
    "publishedAt": "2024-02-27T09:36:26.461Z",
    "updatedAt": "2026-08-05T08:45:05.258Z",
    "importedAt": "2026-10-24T01:56:36.661Z",
    "snapshot": {
      "id": "cve_2026-10-24_midnight_baseline",
      "at": "2026-10-24T00:00:00.000Z",
      "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z"
    },
    "facts": {
      "title": "locking/qrwlock: Fix ordering in queued_write_lock_slowpath()",
      "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nlocking/qrwlock: Fix ordering in queued_write_lock_slowpath()\n\nWhile this code is executed with the wait_lock held, a reader can\nacquire the lock without holding wait_lock.  The writer side loops\nchecking the value with the atomic_cond_read_acquire(), but only truly\nacquires the lock when the compare-and-exchange is completed\nsuccessfully which isn’t ordered. This exposes the window between the\nacquire and the cmpxchg to an A-B-A problem which allows reads\nfollowing the lock acquisition to observe values speculatively before\nthe write lock is truly acquired.\n\nWe've seen a problem in epoll where the reader does a xchg while\nholding the read lock, but the writer can see a value change out from\nunder it.\n\n  Writer                                | Reader\n  --------------------------------------------------------------------------------\n  ep_scan_ready_list()                  |\n  |- write_lock_irq()                   |\n      |- queued_write_lock_slowpath()   |\n\t|- atomic_cond_read_acquire()   |\n\t\t\t\t        | read_lock_irqsave(&ep->lock, flags);\n     --> (observes value before unlock) |  chain_epi_lockless()\n     |                                  |    epi->next = xchg(&ep->ovflist, epi);\n     |                                  | read_unlock_irqrestore(&ep->lock, flags);\n     |                                  |\n     |     atomic_cmpxchg_relaxed()     |\n     |-- READ_ONCE(ep->ovflist);        |\n\nA core can order the read of the ovflist ahead of the\natomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire\nsemantics addresses this issue at which point the atomic_cond_read can\nbe switched to use relaxed semantics.\n\n[peterz: use try_cmpxchg()]",
      "affected": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "b519b56e378ee82caf9b079b04f5db87dedc3251",
              "status": "affected",
              "versionType": "git",
              "lessThan": "5902f9453a313be8fe78cbd7e7ca9dba9319fc6e"
            },
            {
              "version": "b519b56e378ee82caf9b079b04f5db87dedc3251",
              "status": "affected",
              "versionType": "git",
              "lessThan": "82808cc026811fbc3ecf0c0b267a12a339eead56"
            },
            {
              "version": "b519b56e378ee82caf9b079b04f5db87dedc3251",
              "status": "affected",
              "versionType": "git",
              "lessThan": "82fa9ced35d88581cffa4a1c856fc41fca96d80a"
            },
            {
              "version": "b519b56e378ee82caf9b079b04f5db87dedc3251",
              "status": "affected",
              "versionType": "git",
              "lessThan": "d558fcdb17139728347bccc60a16af3e639649d2"
            },
            {
              "version": "b519b56e378ee82caf9b079b04f5db87dedc3251",
              "status": "affected",
              "versionType": "git",
              "lessThan": "84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "versions": [
            {
              "version": "4.15",
              "status": "affected"
            },
            {
              "version": "0",
              "status": "unaffected",
              "versionType": "semver",
              "lessThan": "4.15"
            },
            {
              "version": "4.19.189",
              "status": "unaffected",
              "versionType": "semver",
              "lessThanOrEqual": "4.19.*"
            },
            {
              "version": "5.4.115",
              "status": "unaffected",
              "versionType": "semver",
              "lessThanOrEqual": "5.4.*"
            },
            {
              "version": "5.10.33",
              "status": "unaffected",
              "versionType": "semver",
              "lessThanOrEqual": "5.10.*"
            },
            {
              "version": "5.11.17",
              "status": "unaffected",
              "versionType": "semver",
              "lessThanOrEqual": "5.11.*"
            },
            {
              "version": "5.12",
              "status": "unaffected",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ]
        }
      ]
    }
  }
}