FKIE_CVE-2026-89796

Vulnerability from fkie_nvd - Published: 2026-09-16 11:16 - Updated: 2026-09-21 14:17
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: mm/damon/core: avoid infinite kdamond_merge_regions() internal loop Patch series "mm/damon: unurgent fixes for infinite loop, NULL de-ref and races", v1.1. Sashiko found a few issues in DAMON that could cause infinite loop, NULL dereference and monitoring results degradation. The first two sounds scary but the infinite loop happens only under unreasonable user setup. The NULL dereference is only in a unit test. Monitoring results degradation is trivial since it is only best-effort, and those happens from only unlikely races. Still those are bugs that better to fix if possible. Fix those. This patch (of 6): Due to online parameter update like events, the number of DAMON regions could be higher than the user-set upper limit. kdamond_merge_regions() repeats merge regions until the number meets the limit, while doubling the merge threshold up to the theoretical maximum threshold. It is tried only up to the theoretical maximum threshold because even the aggressive merging can fail from reducing the number of regions under the user-defined upper limit. For example, there could be many user-defined non-contiguous regions that cannot be merged. The threshold based loop break condition is evaluated by comparing the threshold for the next merging try against the theoretical maximum threshold. If max_thres is larger than UINT_MAX / 2, doubling the threshold could make it overflow, and bypass the loop break condition. In the case, if the number of regions cannot be reduced under the upper limit like explained above, the loop will run infinitely. Prevent the case by doing the break condition check before doubling the threshold. Also, prevent the threshold exceeding the maximum threshold, as it could overflow and apply the wrong merge threshold. This issue is unlikely to occur in real world, since having the max_thres higher than UINT_MAX / 2 require unrealistically large aggregation intervals compared to the sampling interval. Also, it requires an unrealistically large number of uncontiguous regions setup. Nonetheless, the consequence is bad and the fix is simple. The issue was discovered [1] by Sashiko.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/123e4619ab6c8ab1c4cb1d7a58311a2af13929cd
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/50a7a5aec1aa43efc297fd4377c1cbdc7d15620d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/769c16699c89811386eb003c8fd9dcb8d405b316
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8a96a06e04d210845be5d9581c0e9e338947e8f8
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/damon/core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "769c16699c89811386eb003c8fd9dcb8d405b316",
              "status": "affected",
              "version": "310d6c15e9104c99d5d9d0ff8e5383a79da7d5e6",
              "versionType": "git"
            },
            {
              "lessThan": "50a7a5aec1aa43efc297fd4377c1cbdc7d15620d",
              "status": "affected",
              "version": "310d6c15e9104c99d5d9d0ff8e5383a79da7d5e6",
              "versionType": "git"
            },
            {
              "lessThan": "8a96a06e04d210845be5d9581c0e9e338947e8f8",
              "status": "affected",
              "version": "310d6c15e9104c99d5d9d0ff8e5383a79da7d5e6",
              "versionType": "git"
            },
            {
              "lessThan": "123e4619ab6c8ab1c4cb1d7a58311a2af13929cd",
              "status": "affected",
              "version": "310d6c15e9104c99d5d9d0ff8e5383a79da7d5e6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "1e865019cef354a5f0314491b4b4fc9f9a613642",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "d7eda72e59bbf3ed592db7ff0fd8c246c73149a8",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "11078e2d11465518a9e85096bd28f8cd5fa1ea41",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "f2bd3184b6aeca6a497394b558337246e09fc02d",
              "versionType": "git"
            },
            {
              "lessThan": "5.16",
              "status": "affected",
              "version": "5.15.164",
              "versionType": "semver"
            },
            {
              "lessThan": "6.2",
              "status": "affected",
              "version": "6.1.101",
              "versionType": "semver"
            },
            {
              "lessThan": "6.7",
              "status": "affected",
              "version": "6.6.41",
              "versionType": "semver"
            },
            {
              "lessThan": "6.10",
              "status": "affected",
              "version": "6.9.10",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "mm/damon/core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.10"
            },
            {
              "lessThan": "6.10",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.111",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/damon/core: avoid infinite kdamond_merge_regions() internal loop\n\nPatch series \"mm/damon: unurgent fixes for infinite loop, NULL de-ref and\nraces\", v1.1.\n\nSashiko found a few issues in DAMON that could cause infinite loop, NULL\ndereference and monitoring results degradation.  The first two sounds\nscary but the infinite loop happens only under unreasonable user setup. \nThe NULL dereference is only in a unit test.  Monitoring results\ndegradation is trivial since it is only best-effort, and those happens\nfrom only unlikely races.  Still those are bugs that better to fix if\npossible.  Fix those.\n\n\nThis patch (of 6):\n\nDue to online parameter update like events, the number of DAMON regions\ncould be higher than the user-set upper limit.  kdamond_merge_regions()\nrepeats merge regions until the number meets the limit, while doubling the\nmerge threshold up to the theoretical maximum threshold.  It is tried only\nup to the theoretical maximum threshold because even the aggressive\nmerging can fail from reducing the number of regions under the\nuser-defined upper limit.  For example, there could be many user-defined\nnon-contiguous regions that cannot be merged.\n\nThe threshold based loop break condition is evaluated by comparing the\nthreshold for the next merging try against the theoretical maximum\nthreshold.  If max_thres is larger than UINT_MAX / 2, doubling the\nthreshold could make it overflow, and bypass the loop break condition.  In\nthe case, if the number of regions cannot be reduced under the upper limit\nlike explained above, the loop will run infinitely.\n\nPrevent the case by doing the break condition check before doubling the\nthreshold.  Also, prevent the threshold exceeding the maximum threshold,\nas it could overflow and apply the wrong merge threshold.\n\nThis issue is unlikely to occur in real world, since having the max_thres\nhigher than UINT_MAX / 2 require unrealistically large aggregation\nintervals compared to the sampling interval.  Also, it requires an\nunrealistically large number of uncontiguous regions setup.  Nonetheless,\nthe consequence is bad and the fix is simple.\n\nThe issue was discovered [1] by Sashiko."
    }
  ],
  "id": "CVE-2026-89796",
  "lastModified": "2026-09-21T14:17:26.750",
  "metrics": {},
  "published": "2026-09-16T11:16:44.423",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/123e4619ab6c8ab1c4cb1d7a58311a2af13929cd"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/50a7a5aec1aa43efc297fd4377c1cbdc7d15620d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/769c16699c89811386eb003c8fd9dcb8d405b316"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/8a96a06e04d210845be5d9581c0e9e338947e8f8"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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