FKIE_CVE-2026-98104

Vulnerability from fkie_nvd - Published: 2026-09-25 11:17 - Updated: 2026-10-19 10:18
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted gen_new_kid() falls back to returning max (htid | 0xFFF) when both idr_alloc_u32() ranges are full, instead of reporting an error. u32_change() trusts that value and inserts a new knode with a handle that is already live in the hash table, breaking handle uniqueness within the table's node ID space. The handle was never reserved in ht->handle_idr, so every later error path that does idr_remove(&ht->handle_idr, handle) removes the reservation of a different, live knode, which is then reused — one failed add compounds into further duplicates. The 4095 limit is per (table, bucket) — ht->handle_idr is per hash table and the range is derived from htid (bucketid), so a table with divisor 256 can legitimately hold 256*4095 knodes. The sibling helper gen_new_htid() has the same silent in-band failure: it returns 0 when the tp_c handle pool (1..0x7FF) is full, and u32_init() publishes the root hash table with handle 0 without checking. Two root tables with handle 0 alias in u32_lookup_ht(), allowing cross-tcf_proto knode add/lookup/delete. Add the same exhaustion check that the divisor path already has. Return an error so u32_change() fails with ENOSPC/ENOMEM when the node ID space is exhausted, and so u32_init() fails with -ENOMEM when the hash table ID space is exhausted. The extack message distinguishes pool exhaustion (-ENOSPC) from a transient allocation failure (-ENOMEM). Conditions to recreate the bug: - CONFIG_NET_SCHED=y, CONFIG_CLS_U32=y (or =m with module loaded) - Create a clsact qdisc on a device, then add 4095 u32 filters with auto-generated handles to fill the node ID space for the root hash table (single bucket). The 4096th auto-handle filter add triggers the duplicate handle (fh 800::fff reused). Reachable at Level 2 (unshare -Urn, namespace-local CAP_NET_ADMIN). - For gen_new_htid: create 2047 u32 proto entries on the same block to fill the tp_c handle pool, then create one more. The root table gets handle 0 and aliases with other handle-0 root tables.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/6890e28840bae4f6805e8de981c4ec8e12a4e064
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/84223baf21bc9b008444ae9bc38d5fb91fe00b9d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f4ee13ed7f7b22dcd8287fcf477ae37bd84567da
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f594f04268d01c5fdc975f3f51fc219ea2159ac6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/feab9261b537df4ebb8350e4779bc185373059fd
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/cls_u32.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f4ee13ed7f7b22dcd8287fcf477ae37bd84567da",
              "status": "affected",
              "version": "7801db8aec957fa6610efe0ee26a6c8bc0f1d73b",
              "versionType": "git"
            },
            {
              "lessThan": "84223baf21bc9b008444ae9bc38d5fb91fe00b9d",
              "status": "affected",
              "version": "7801db8aec957fa6610efe0ee26a6c8bc0f1d73b",
              "versionType": "git"
            },
            {
              "lessThan": "6890e28840bae4f6805e8de981c4ec8e12a4e064",
              "status": "affected",
              "version": "7801db8aec957fa6610efe0ee26a6c8bc0f1d73b",
              "versionType": "git"
            },
            {
              "lessThan": "feab9261b537df4ebb8350e4779bc185373059fd",
              "status": "affected",
              "version": "7801db8aec957fa6610efe0ee26a6c8bc0f1d73b",
              "versionType": "git"
            },
            {
              "lessThan": "f594f04268d01c5fdc975f3f51fc219ea2159ac6",
              "status": "affected",
              "version": "7801db8aec957fa6610efe0ee26a6c8bc0f1d73b",
              "versionType": "git"
            },
            {
              "lessThan": "d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f",
              "status": "affected",
              "version": "7801db8aec957fa6610efe0ee26a6c8bc0f1d73b",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/sched/cls_u32.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "3.16"
            },
            {
              "lessThan": "3.16",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.189",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.158",
              "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": "7.2.7",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "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\nnet/sched: cls_u32: fix duplicate handle when node ID pool is exhausted\n\ngen_new_kid() falls back to returning max (htid | 0xFFF) when both\nidr_alloc_u32() ranges are full, instead of reporting an error.\nu32_change() trusts that value and inserts a new knode with a handle\nthat is already live in the hash table, breaking handle uniqueness\nwithin the table\u0027s node ID space.\n\nThe handle was never reserved in ht-\u003ehandle_idr, so every later error\npath that does idr_remove(\u0026ht-\u003ehandle_idr, handle) removes the\nreservation of a different, live knode, which is then reused \u2014 one\nfailed add compounds into further duplicates.\n\nThe 4095 limit is per (table, bucket) \u2014 ht-\u003ehandle_idr is per hash\ntable and the range is derived from htid (bucketid), so a table with\ndivisor 256 can legitimately hold 256*4095 knodes.\n\nThe sibling helper gen_new_htid() has the same silent in-band failure:\nit returns 0 when the tp_c handle pool (1..0x7FF) is full, and\nu32_init() publishes the root hash table with handle 0 without\nchecking.  Two root tables with handle 0 alias in u32_lookup_ht(),\nallowing cross-tcf_proto knode add/lookup/delete.  Add the same\nexhaustion check that the divisor path already has.\n\nReturn an error so u32_change() fails with ENOSPC/ENOMEM when the\nnode ID space is exhausted, and so u32_init() fails with -ENOMEM\nwhen the hash table ID space is exhausted.  The extack message\ndistinguishes pool exhaustion (-ENOSPC) from a transient allocation\nfailure (-ENOMEM).\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED=y, CONFIG_CLS_U32=y (or =m with module loaded)\n- Create a clsact qdisc on a device, then add 4095 u32 filters with\n  auto-generated handles to fill the node ID space for the root hash\n  table (single bucket). The 4096th auto-handle filter add triggers\n  the duplicate handle (fh 800::fff reused). Reachable at Level 2\n  (unshare -Urn, namespace-local CAP_NET_ADMIN).\n- For gen_new_htid: create 2047 u32 proto entries on the same block\n  to fill the tp_c handle pool, then create one more. The root table\n  gets handle 0 and aliases with other handle-0 root tables."
    }
  ],
  "id": "CVE-2026-98104",
  "lastModified": "2026-10-19T10:18:07.770",
  "metrics": {},
  "published": "2026-09-25T11:17:40.793",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/6890e28840bae4f6805e8de981c4ec8e12a4e064"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/84223baf21bc9b008444ae9bc38d5fb91fe00b9d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f4ee13ed7f7b22dcd8287fcf477ae37bd84567da"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f594f04268d01c5fdc975f3f51fc219ea2159ac6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/feab9261b537df4ebb8350e4779bc185373059fd"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

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.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON
How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

Loading timeline…




    Related by attack behaviour

    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.