Description
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.
Published: 2026-09-25
Score: n/a
EPSS: n/a
KEV: No
AI Analysis

Analysis and contextual insights are available on OpenCVE Cloud.

Remediation

No vendor fix or workaround currently provided.

Additional remediation guidance may be available on OpenCVE Cloud.

Tracking

Sign in to view the affected projects.

Advisories

No advisories yet.

History

Fri, 25 Sep 2026 13:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-665

Fri, 25 Sep 2026 10:45:00 +0000

Type Values Removed Values Added
Description 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.
Title net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-25T10:35:54.544Z

Reserved: 2026-09-25T10:25:14.315Z

Link: CVE-2026-98104

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-25T11:17:40.793

Modified: 2026-09-25T11:17:40.793

Link: CVE-2026-98104

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-25T14:30:14Z

Weaknesses