CVE-2026-31649 (GCVE-0-2026-31649)
Vulnerability from cvelistv5
Published
2026-04-24 14:45
Modified
2026-04-27 14:04
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net: stmmac: fix integer underflow in chain mode The jumbo_frm() chain-mode implementation unconditionally computes len = nopaged_len - bmax; where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is BUF_SIZE_8KiB or BUF_SIZE_2KiB. However, the caller stmmac_xmit() decides to invoke jumbo_frm() based on skb->len (total length including page fragments): is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc); When a packet has a small linear portion (nopaged_len <= bmax) but a large total length due to page fragments (skb->len > bmax), the subtraction wraps as an unsigned integer, producing a huge len value (~0xFFFFxxxx). This causes the while (len != 0) loop to execute hundreds of thousands of iterations, passing skb->data + bmax * i pointers far beyond the skb buffer to dma_map_single(). On IOMMU-less SoCs (the typical deployment for stmmac), this maps arbitrary kernel memory to the DMA engine, constituting a kernel memory disclosure and potential memory corruption from hardware. Fix this by introducing a buf_len local variable clamped to min(nopaged_len, bmax). Computing len = nopaged_len - buf_len is then always safe: it is zero when the linear portion fits within a single descriptor, causing the while (len != 0) loop to be skipped naturally, and the fragment loop in stmmac_xmit() handles page fragments afterward.
References
Impacted products
Vendor Product Version
Linux Linux Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
Version: 286a837217204b1ef105e3a554d0757e4fdfaac1
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/ethernet/stmicro/stmmac/chain_mode.c"
          ],
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          ],
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          "vendor": "Linux",
          "versions": [
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              "version": "3.2"
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              "version": "0",
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              "status": "unaffected",
              "version": "5.10.253",
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            },
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              "status": "unaffected",
              "version": "6.1.169",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.135",
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            },
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              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.82",
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            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.23",
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            },
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              "status": "unaffected",
              "version": "6.19.13",
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            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.0",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              ],
              "negate": false,
              "operator": "OR"
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          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: stmmac: fix integer underflow in chain mode\n\nThe jumbo_frm() chain-mode implementation unconditionally computes\n\n    len = nopaged_len - bmax;\n\nwhere nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is\nBUF_SIZE_8KiB or BUF_SIZE_2KiB.  However, the caller stmmac_xmit()\ndecides to invoke jumbo_frm() based on skb-\u003elen (total length including\npage fragments):\n\n    is_jumbo = stmmac_is_jumbo_frm(priv, skb-\u003elen, enh_desc);\n\nWhen a packet has a small linear portion (nopaged_len \u003c= bmax) but a\nlarge total length due to page fragments (skb-\u003elen \u003e bmax), the\nsubtraction wraps as an unsigned integer, producing a huge len value\n(~0xFFFFxxxx).  This causes the while (len != 0) loop to execute\nhundreds of thousands of iterations, passing skb-\u003edata + bmax * i\npointers far beyond the skb buffer to dma_map_single().  On IOMMU-less\nSoCs (the typical deployment for stmmac), this maps arbitrary kernel\nmemory to the DMA engine, constituting a kernel memory disclosure and\npotential memory corruption from hardware.\n\nFix this by introducing a buf_len local variable clamped to\nmin(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then\nalways safe: it is zero when the linear portion fits within a single\ndescriptor, causing the while (len != 0) loop to be skipped naturally,\nand the fragment loop in stmmac_xmit() handles page fragments afterward."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-27T14:04:42.760Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48"
        },
        {
          "url": "https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b"
        },
        {
          "url": "https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f"
        },
        {
          "url": "https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef"
        },
        {
          "url": "https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d"
        },
        {
          "url": "https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803"
        },
        {
          "url": "https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb"
        },
        {
          "url": "https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67"
        }
      ],
      "title": "net: stmmac: fix integer underflow in chain mode",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31649",
    "datePublished": "2026-04-24T14:45:02.520Z",
    "dateReserved": "2026-03-09T15:48:24.128Z",
    "dateUpdated": "2026-04-27T14:04:42.760Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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