FKIE_CVE-2026-63836

Vulnerability from fkie_nvd - Published: 2026-07-19 12:16 - Updated: 2026-07-19 12:16
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: batman-adv: tp_meter: avoid divide-by-zero for dec_cwnd The cwnd is always MSS <= cwnd <= 0x20000000. But the calculation in batadv_tp_update_cwnd() assumes unsigned 32 bit arithmetics. ((mss * 8) ** 2) / (cwnd * 8) In case cwnd is actually 0x20000000, it will be shifted by 3 bit to the left end up at 0x100000000 or U32_MAX + 1. It will therefore wrap around and be 0 - resulting in: ((mss * 8) ** 2) / 0 This is of course invalid and cannot be calculated. The calculation should must be simplified to avoid this overflow: (mss ** 2) * 8 / cwnd It will keep the precision enhancement from the scaling (by 8) but avoid the overflow in the divisor. In theory, there could still be an overflow in the dividend. It is at the moment fixed to BATADV_TP_PLEN in batadv_tp_recv_ack() - so it is not an imminent problem. But allowing it to use the whole u32 bit range, would mean that it can still use up to 67 bits. To keep this calculation safe for 32 bit arithmetic, mss must never use more than floor((32 - 3) / 2) bits - or in other words: must never be larger than 16383.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1381b021bf886b793fa5ffb895a8efae7ba0318f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/33ccd52f3cc9ed46ce395199f89aa3234dc83314
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/35264c4d46067d6312871488c810cef387f8c1f6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/585616dab0aa9c45bc11b2c8082ca78533bc00e9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7d2a44bc6bbe39aed03c68864aa0e54e04a50278
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/cd74176cf1685f35a2e5f212d15748bbfecb53b6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d08b69da40a101df1e28bfe1e8fa7a09ffa41107
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/batman-adv/tp_meter.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "35264c4d46067d6312871488c810cef387f8c1f6",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "1381b021bf886b793fa5ffb895a8efae7ba0318f",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "d08b69da40a101df1e28bfe1e8fa7a09ffa41107",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "cd74176cf1685f35a2e5f212d15748bbfecb53b6",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "7d2a44bc6bbe39aed03c68864aa0e54e04a50278",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "585616dab0aa9c45bc11b2c8082ca78533bc00e9",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            },
            {
              "lessThan": "33ccd52f3cc9ed46ce395199f89aa3234dc83314",
              "status": "affected",
              "version": "33a3bb4a3345bb511f9c69c913da95d4693e2a4e",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/batman-adv/tp_meter.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.8"
            },
            {
              "lessThan": "4.8",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.260",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.211",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.177",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.144",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.95",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.38",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.3",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2-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\nbatman-adv: tp_meter: avoid divide-by-zero for dec_cwnd\n\nThe cwnd is always MSS \u003c= cwnd \u003c= 0x20000000. But the calculation in\nbatadv_tp_update_cwnd() assumes unsigned 32 bit arithmetics.\n\n    ((mss * 8) ** 2) / (cwnd * 8)\n\nIn case cwnd is actually 0x20000000, it will be shifted by 3 bit to the\nleft end up at 0x100000000 or U32_MAX + 1. It will therefore wrap around\nand be 0 - resulting in:\n\n    ((mss * 8) ** 2) / 0\n\nThis is of course invalid and cannot be calculated. The calculation should\nmust be simplified to avoid this overflow:\n\n   (mss ** 2) * 8 / cwnd\n\nIt will keep the precision enhancement from the scaling (by 8) but avoid\nthe overflow in the divisor.\n\nIn theory, there could still be an overflow in the dividend. It is at the\nmoment fixed to BATADV_TP_PLEN in batadv_tp_recv_ack() - so it is not an\nimminent problem. But allowing it to use the whole u32 bit range, would\nmean that it can still use up to 67 bits. To keep this calculation safe for\n32 bit arithmetic, mss must never use more than floor((32 - 3) / 2) bits -\nor in other words: must never be larger than 16383."
    }
  ],
  "id": "CVE-2026-63836",
  "lastModified": "2026-07-19T12:16:57.103",
  "metrics": {},
  "published": "2026-07-19T12:16:57.103",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/1381b021bf886b793fa5ffb895a8efae7ba0318f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/33ccd52f3cc9ed46ce395199f89aa3234dc83314"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/35264c4d46067d6312871488c810cef387f8c1f6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/585616dab0aa9c45bc11b2c8082ca78533bc00e9"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7d2a44bc6bbe39aed03c68864aa0e54e04a50278"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/cd74176cf1685f35a2e5f212d15748bbfecb53b6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d08b69da40a101df1e28bfe1e8fa7a09ffa41107"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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