CVE-2021-46974 (GCVE-0-2021-46974)

Vulnerability from cvelistv5 – Published: 2024-02-27 18:47 – Updated: 2026-08-05 08:45
VLAI
Title
bpf: Fix masking negation logic upon negative dst register
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix masking negation logic upon negative dst register The negation logic for the case where the off_reg is sitting in the dst register is not correct given then we cannot just invert the add to a sub or vice versa. As a fix, perform the final bitwise and-op unconditionally into AX from the off_reg, then move the pointer from the src to dst and finally use AX as the source for the original pointer arithmetic operation such that the inversion yields a correct result. The single non-AX mov in between is possible given constant blinding is retaining it as it's not an immediate based operation.
Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-03-05 16:32 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: ae03b6b1c880a03d4771257336dc3bca156dd51b , < 4d542ddb88fb2f39bf7f14caa2902f3e8d06f6ba (git)
Affected: f92a819b4cbef8c9527d9797110544b2055a4b96 , < 0e2dfdc74a7f4036127356d42ea59388f153f42c (git)
Affected: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 , < 53e0db429b37a32b8fc706d0d90eb4583ad13848 (git)
Affected: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 , < 2cfa537674cd1051a3b8111536d77d0558f33d5d (git)
Affected: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 , < 6eba92a4d4be8feb4dc33976abac544fa99d6ecc (git)
Affected: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 , < 7cf64d8679ca1cb20cf57d6a88bfee79a0922a66 (git)
Affected: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 , < b9b34ddbe2076ade359cd5ce7537d5ed019e9807 (git)
Affected: 078da99d449f64ca04d459cdbdcce513b64173cd (git)
Affected: 4.14.113 , < 4.14.233 (semver)
Affected: 4.19.19 , < 4.19.190 (semver)
Affected: 4.20.6 , < 4.21 (semver)
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Linux Linux Affected: 5.0
Unaffected: 0 , < 5.0 (semver)
Unaffected: 4.14.233 , ≤ 4.14.* (semver)
Unaffected: 4.19.190 , ≤ 4.19.* (semver)
Unaffected: 5.4.117 , ≤ 5.4.* (semver)
Unaffected: 5.10.35 , ≤ 5.10.* (semver)
Unaffected: 5.11.19 , ≤ 5.11.* (semver)
Unaffected: 5.12.2 , ≤ 5.12.* (semver)
Unaffected: 5.13 , ≤ * (original_commit_for_fix)
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                  "version": "979d63d50c0c0f7bc537bf821e056cc9fe5abd38",
                  "versionType": "git"
                },
                {
                  "status": "affected",
                  "version": "078da99d449f64ca04d459cdbdcce513b64173cd",
                  "versionType": "git"
                },
                {
                  "lessThan": "4.14.233",
                  "status": "affected",
                  "version": "4.14.113",
                  "versionType": "semver"
                },
                {
                  "lessThan": "4.19.190",
                  "status": "affected",
                  "version": "4.19.19",
                  "versionType": "semver"
                },
                {
                  "lessThan": "4.21",
                  "status": "affected",
                  "version": "4.20.6",
                  "versionType": "semver"
                }
              ]
            },
            {
              "defaultStatus": "affected",
              "product": "Linux",
              "programFiles": [
                "kernel/bpf/verifier.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "status": "affected",
                  "version": "5.0"
                },
                {
                  "lessThan": "5.0",
                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "4.14.*",
                  "status": "unaffected",
                  "version": "4.14.233",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "4.19.*",
                  "status": "unaffected",
                  "version": "4.19.190",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.4.*",
                  "status": "unaffected",
                  "version": "5.4.117",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.10.*",
                  "status": "unaffected",
                  "version": "5.10.35",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.11.*",
                  "status": "unaffected",
                  "version": "5.11.19",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.12.*",
                  "status": "unaffected",
                  "version": "5.12.2",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "5.13",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "4.14.233",
                      "versionStartIncluding": "4.14.113",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "4.19.190",
                      "versionStartIncluding": "4.19.19",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.4.117",
                      "versionStartIncluding": "5.0",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.10.35",
                      "versionStartIncluding": "5.0",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.11.19",
                      "versionStartIncluding": "5.0",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.12.2",
                      "versionStartIncluding": "5.0",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.13",
                      "versionStartIncluding": "5.0",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "4.20.6",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix masking negation logic upon negative dst register\n\nThe negation logic for the case where the off_reg is sitting in the\ndst register is not correct given then we cannot just invert the add\nto a sub or vice versa. As a fix, perform the final bitwise and-op\nunconditionally into AX from the off_reg, then move the pointer from\nthe src to dst and finally use AX as the source for the original\npointer arithmetic operation such that the inversion yields a correct\nresult. The single non-AX mov in between is possible given constant\nblinding is retaining it as it\u0027s not an immediate based operation."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 7.1,
                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
                "version": "3.1"
              },
              "scenarios": [
                {
                  "lang": "en",
                  "value": "AV:L - The bug is reached by loading a crafted eBPF program via the bpf() syscall (socket filter / cgroup skb); it is not reachable from the network stack or remote protocols.\nAC:L - An attacker fully controls the BPF program and map layout and can reliably hit the isneg \u0026\u0026 !issrc sanitization path; no conditions beyond attacker control are required.\nPR:L - Unprivileged users can load SOCKET_FILTER/CGROUP_SKB programs when unprivileged BPF is enabled (the default when this bug was live), and only that non-bypass_spec_v1 path applies the broken rewrite.\nUI:N - Exploitation requires no victim action; the attacker loads and triggers their own BPF program.\nS:U - Impact stays within the host kernel authority (local kernel memory disclosure / crash); there is no VM, IOMMU, or other security-authority boundary crossed.\nC:H - The broken mask defeats Spectre v1 pointer-arithmetic sanitation for negative dst offsets, enabling speculative out-of-bounds loads that can disclose arbitrary kernel memory via side channels (same class as CVE-2020-27170/27171 and CVE-2021-29155).\nI:N - The failure yields speculative reads and architecturally wild pointers that typically fault rather than a controllable write primitive; Spectre-style BPF masking bugs do not provide integrity impact.\nA:H - The incorrect add/sub inversion for negative dst produces architecturally wrong pointers (e.g. offset - pointer), so subsequent verifier-approved loads/stores oops/panic the kernel."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:45:20.335Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/4d542ddb88fb2f39bf7f14caa2902f3e8d06f6ba"
            },
            {
              "url": "https://git.kernel.org/stable/c/0e2dfdc74a7f4036127356d42ea59388f153f42c"
            },
            {
              "url": "https://git.kernel.org/stable/c/53e0db429b37a32b8fc706d0d90eb4583ad13848"
            },
            {
              "url": "https://git.kernel.org/stable/c/2cfa537674cd1051a3b8111536d77d0558f33d5d"
            },
            {
              "url": "https://git.kernel.org/stable/c/6eba92a4d4be8feb4dc33976abac544fa99d6ecc"
            },
            {
              "url": "https://git.kernel.org/stable/c/7cf64d8679ca1cb20cf57d6a88bfee79a0922a66"
            },
            {
              "url": "https://git.kernel.org/stable/c/b9b34ddbe2076ade359cd5ce7537d5ed019e9807"
            }
          ],
          "title": "bpf: Fix masking negation logic upon negative dst register",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-46974",
        "datePublished": "2024-02-27T18:47:08.487Z",
        "dateReserved": "2024-02-27T18:42:55.944Z",
        "dateUpdated": "2026-08-05T08:45:20.335Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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.

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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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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.