{
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    "dataVersion": "5.1",
    "cveMetadata": {
        "cveId": "CVE-2021-46921",
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "state": "PUBLISHED",
        "assignerShortName": "Linux",
        "dateReserved": "2024-02-25T13:45:52.719Z",
        "datePublished": "2024-02-27T09:36:26.461Z",
        "dateUpdated": "2024-08-04T05:17:42.848Z"
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                "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
                "shortName": "Linux",
                "dateUpdated": "2024-05-29T04:58:53.166Z"
            },
            "descriptions": [
                {
                    "lang": "en",
                    "value": "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": [
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                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "kernel/locking/qrwlock.c"
                    ],
                    "versions": [
                        {
                            "version": "b519b56e378e",
                            "lessThan": "5902f9453a31",
                            "status": "affected",
                            "versionType": "git"
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                        {
                            "version": "b519b56e378e",
                            "lessThan": "82808cc02681",
                            "status": "affected",
                            "versionType": "git"
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                    ]
                },
                {
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "kernel/locking/qrwlock.c"
                    ],
                    "versions": [
                        {
                            "version": "4.15",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "4.15",
                            "status": "unaffected",
                            "versionType": "custom"
                        },
                        {
                            "version": "4.19.189",
                            "lessThanOrEqual": "4.19.*",
                            "status": "unaffected",
                            "versionType": "custom"
                        },
                        {
                            "version": "5.4.115",
                            "lessThanOrEqual": "5.4.*",
                            "status": "unaffected",
                            "versionType": "custom"
                        },
                        {
                            "version": "5.10.33",
                            "lessThanOrEqual": "5.10.*",
                            "status": "unaffected",
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                        {
                            "version": "5.11.17",
                            "lessThanOrEqual": "5.11.*",
                            "status": "unaffected",
                            "versionType": "custom"
                        },
                        {
                            "version": "5.12",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
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                }
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            "references": [
                {
                    "url": "https://git.kernel.org/stable/c/5902f9453a313be8fe78cbd7e7ca9dba9319fc6e"
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                },
                {
                    "url": "https://git.kernel.org/stable/c/84a24bf8c52e66b7ac89ada5e3cfbe72d65c1896"
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            ],
            "title": "locking/qrwlock: Fix ordering in queued_write_lock_slowpath()",
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