CVE-2026-98104
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.
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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).
Detalles técnicos trazas, registros y código del informe original
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.
CVSS
NVD no ha asignado puntuación CVSS a esta CVE (habitual desde el cambio de política de abril de 2026).
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.21%
- Percentil entre todas las CVEs puntuadas: 10
- Fecha de la puntuación: 5/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
- https://git.kernel.org/stable/c/6890e28840bae4f6805e8de981c4ec8e12a4e064
- https://git.kernel.org/stable/c/84223baf21bc9b008444ae9bc38d5fb91fe00b9d
- https://git.kernel.org/stable/c/d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f
- https://git.kernel.org/stable/c/f4ee13ed7f7b22dcd8287fcf477ae37bd84567da
- https://git.kernel.org/stable/c/f594f04268d01c5fdc975f3f51fc219ea2159ac6
- https://git.kernel.org/stable/c/feab9261b537df4ebb8350e4779bc185373059fd
JSON original (NVD)
Mostrar
{
"id": "CVE-2026-98104",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"programFiles": [
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"version": "3.16"
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{
"status": "unaffected",
"version": "0",
"lessThan": "3.16",
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{
"status": "unaffected",
"version": "6.1.189",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
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{
"status": "unaffected",
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"versionType": "semver",
"lessThanOrEqual": "6.6.*"
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{
"status": "unaffected",
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{
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"version": "6.18.53",
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{
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{
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],
"published": "2026-09-25T11:17:40.793",
"references": [
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}
],
"vulnStatus": "Undergoing Analysis",
"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's node ID space.\n\nThe handle was never reserved in ht->handle_idr, so every later error\npath that does idr_remove(&ht->handle_idr, handle) removes the\nreservation of a different, live knode, which is then reused — one\nfailed add compounds into further duplicates.\n\nThe 4095 limit is per (table, bucket) — ht->handle_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."
}
],
"lastModified": "2026-10-03T11:18:32.590",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}