CVE-2025-21647
Vulnerability from cvelistv5
Published
2025-01-19 10:18
Modified
2025-01-20 06:30
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: sched: sch_cake: add bounds checks to host bulk flow fairness counts Even though we fixed a logic error in the commit cited below, syzbot still managed to trigger an underflow of the per-host bulk flow counters, leading to an out of bounds memory access. To avoid any such logic errors causing out of bounds memory accesses, this commit factors out all accesses to the per-host bulk flow counters to a series of helpers that perform bounds-checking before any increments and decrements. This also has the benefit of improving readability by moving the conditional checks for the flow mode into these helpers, instead of having them spread out throughout the code (which was the cause of the original logic error). As part of this change, the flow quantum calculation is consolidated into a helper function, which means that the dithering applied to the ost load scaling is now applied both in the DRR rotation and when a sparse flow's quantum is first initiated. The only user-visible effect of this is that the maximum packet size that can be sent while a flow stays sparse will now vary with +/- one byte in some cases. This should not make a noticeable difference in practice, and thus it's not worth complicating the code to preserve the old behaviour.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/27202e2e8721c3b23831563c36ed5ac7818641ba
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/737d4d91d35b5f7fa5bb442651472277318b0bfd
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/91bb18950b88f955838ec0c1d97f74d135756dc7
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a777e06dfc72bed73c05dcb437d7c27ad5f90f3f
Impacted products
Vendor Product Version
Linux Linux Version: 549e407569e08459d16122341d332cb508024094
Version: d4a9039a7b3d8005b90c7b1a55a306444f0e5447
Version: 546ea84d07e3e324644025e2aae2d12ea4c5896e
Version: 546ea84d07e3e324644025e2aae2d12ea4c5896e
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   Linux Linux Version: 6.11
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_cake.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "6.11"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.125",
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              "status": "unaffected",
              "version": "6.6.72",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.13",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched: sch_cake: add bounds checks to host bulk flow fairness counts\n\nEven though we fixed a logic error in the commit cited below, syzbot\nstill managed to trigger an underflow of the per-host bulk flow\ncounters, leading to an out of bounds memory access.\n\nTo avoid any such logic errors causing out of bounds memory accesses,\nthis commit factors out all accesses to the per-host bulk flow counters\nto a series of helpers that perform bounds-checking before any\nincrements and decrements. This also has the benefit of improving\nreadability by moving the conditional checks for the flow mode into\nthese helpers, instead of having them spread out throughout the\ncode (which was the cause of the original logic error).\n\nAs part of this change, the flow quantum calculation is consolidated\ninto a helper function, which means that the dithering applied to the\nost load scaling is now applied both in the DRR rotation and when a\nsparse flow\u0027s quantum is first initiated. The only user-visible effect\nof this is that the maximum packet size that can be sent while a flow\nstays sparse will now vary with +/- one byte in some cases. This should\nnot make a noticeable difference in practice, and thus it\u0027s not worth\ncomplicating the code to preserve the old behaviour."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-01-20T06:30:06.822Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a777e06dfc72bed73c05dcb437d7c27ad5f90f3f"
        },
        {
          "url": "https://git.kernel.org/stable/c/27202e2e8721c3b23831563c36ed5ac7818641ba"
        },
        {
          "url": "https://git.kernel.org/stable/c/91bb18950b88f955838ec0c1d97f74d135756dc7"
        },
        {
          "url": "https://git.kernel.org/stable/c/737d4d91d35b5f7fa5bb442651472277318b0bfd"
        }
      ],
      "title": "sched: sch_cake: add bounds checks to host bulk flow fairness counts",
      "x_generator": {
        "engine": "bippy-5f407fcff5a0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21647",
    "datePublished": "2025-01-19T10:18:04.415Z",
    "dateReserved": "2024-12-29T08:45:45.728Z",
    "dateUpdated": "2025-01-20T06:30:06.822Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-21647\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-01-19T11:15:10.307\",\"lastModified\":\"2025-01-19T11:15:10.307\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nsched: sch_cake: add bounds checks to host bulk flow fairness counts\\n\\nEven though we fixed a logic error in the commit cited below, syzbot\\nstill managed to trigger an underflow of the per-host bulk flow\\ncounters, leading to an out of bounds memory access.\\n\\nTo avoid any such logic errors causing out of bounds memory accesses,\\nthis commit factors out all accesses to the per-host bulk flow counters\\nto a series of helpers that perform bounds-checking before any\\nincrements and decrements. This also has the benefit of improving\\nreadability by moving the conditional checks for the flow mode into\\nthese helpers, instead of having them spread out throughout the\\ncode (which was the cause of the original logic error).\\n\\nAs part of this change, the flow quantum calculation is consolidated\\ninto a helper function, which means that the dithering applied to the\\nost load scaling is now applied both in the DRR rotation and when a\\nsparse flow\u0027s quantum is first initiated. The only user-visible effect\\nof this is that the maximum packet size that can be sent while a flow\\nstays sparse will now vary with +/- one byte in some cases. This should\\nnot make a noticeable difference in practice, and thus it\u0027s not worth\\ncomplicating the code to preserve the old behaviour.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/27202e2e8721c3b23831563c36ed5ac7818641ba\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/737d4d91d35b5f7fa5bb442651472277318b0bfd\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/91bb18950b88f955838ec0c1d97f74d135756dc7\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a777e06dfc72bed73c05dcb437d7c27ad5f90f3f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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