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416baaa9-dc9f-4396-8d5f-8c081fb06d67CVE-2021-46921

HistoryFeb 27, 2024 - 10:15 a.m.

CVE-2021-46921

2024-02-2710:15:06

CWE-668

416baaa9-dc9f-4396-8d5f-8c081fb06d67

web.nvd.nist.gov

496

linux kernel

vulnerability

fixing

queued_write_lock_slowpath

a-b-a problem

atomic_cmpxchg_relaxed

nvd

cve-2021-46921

5.5 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

NONE

Availability Impact

NONE

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

6.3 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

15.5%

JSON

In the Linux kernel, the following vulnerability has been resolved:

locking/qrwlock: Fix ordering in queued_write_lock_slowpath()

While this code is executed with the wait_lock held, a reader can
acquire the lock without holding wait_lock. The writer side loops
checking the value with the atomic_cond_read_acquire(), but only truly
acquires the lock when the compare-and-exchange is completed
successfully which isn’t ordered. This exposes the window between the
acquire and the cmpxchg to an A-B-A problem which allows reads
following the lock acquisition to observe values speculatively before
the write lock is truly acquired.

We’ve seen a problem in epoll where the reader does a xchg while
holding the read lock, but the writer can see a value change out from
under it.

Writer | Reader

A core can order the read of the ovflist ahead of the
atomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire
semantics addresses this issue at which point the atomic_cond_read can
be switched to use relaxed semantics.

[peterz: use try_cmpxchg()]

Affected configurations

Vulners

NVD

Node

linuxlinux_kernelRange4.15–4.19.189

linuxlinux_kernelRange4.20.0–5.4.115

linuxlinux_kernelRange5.5.0–5.10.33

linuxlinux_kernelRange5.11.0–5.11.17

linuxlinux_kernelRange5.12.0≥

VendorProductVersionCPE
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

Vendor	Product	Version	CPE
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::

CNA Affected

[
  {
    "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"
      },
      {
        "version": "b519b56e378e",
        "lessThan": "82808cc02681",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "b519b56e378e",
        "lessThan": "82fa9ced35d8",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "b519b56e378e",
        "lessThan": "d558fcdb1713",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "b519b56e378e",
        "lessThan": "84a24bf8c52e",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "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",
        "versionType": "custom"
      },
      {
        "version": "5.11.17",
        "lessThanOrEqual": "5.11.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.12",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]