CVE-2026-98629
Received Received - Intake

Linux Kernel cls_u32 Hash Table Handle IDR Aliasing Fix

Publication date: 2026-10-18

Last updated on: 2026-10-18

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: fix manual hash table handle IDR aliasing A u32 hash table created with an explicit handle ('tc filter add ... handle 801: u32 divisor N') keys its IDR entry on the raw handle, while the destroy paths free it under handle2id(handle). The two key domains disagree for handles in the 0x800..0xFFF htid range: handle2id() folds them back into the auto-allocated id space (1..0x7FF). A manual table therefore leaves its raw-keyed IDR entry unreachable on delete (a permanent leak), and its delete can drop the idr entry of an unrelated live auto table. A later auto allocation can then hand out a handle that aliases the live manual table; u32_lookup_ht() first-match routes lookups and TCA_U32_LINK for that htid to the wrong table. Key the divisor-path alloc on handle2id(handle) so allocation and removal share one key domain. A manual handle that maps onto an id already in use is rejected with -ENOSPC, and auto allocation skips ids held by live manual tables. Conditions to recreate: ip link add test0 type dummy tc qdisc add dev test0 clsact tc filter add dev test0 ingress protocol ip pref 1 \ handle 801: u32 divisor 16 tc filter add dev test0 ingress protocol ip pref 2 u32 divisor 16 tc -d filter show dev test0 ingress | grep 'fh 801:' # unpatched: two live tables with handle 0x80100000 (the pref 2 root # hnode is auto-allocated id 1); patched: the auto hnode takes id 2. Also tested with a poc with a live u32 table on the block, add/delete a manual table 'handle 901: u32 divisor 1' twice; unpatched, the re-add fails with -ENOSPC because the raw key leaked on the first delete.

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Meta Information

Published
2026-10-18
Last Modified
2026-10-18
Generated
2026-10-18
AI Q&A
2026-10-18
EPSS Evaluated
N/A
NVD
CVE-2026-98629
EUVD
EUVD-2026-103543

Affected Vendors & Products

Showing 11 associated CPEs
Vendor Product Version / Range
Linux Linux 9b2c3184e126b941dfa716b8128ed6db92a64e2f
Linux Linux 789f9963bd031c3a185605665b744912df8e7eda
Linux Linux 73af53d82076bbe184d9ece9e14b0dc8599e6055
Linux Linux 73af53d82076bbe184d9ece9e14b0dc8599e6055
Linux Linux 73af53d82076bbe184d9ece9e14b0dc8599e6055
Linux Linux 73af53d82076bbe184d9ece9e14b0dc8599e6055
Linux Linux 4403f9293ce9ecc2a55c688d84ee37e3ba0fc1a8
Linux Linux 6.1.119
Linux Linux 6.6.63
Linux Linux 6.11.10
Linux Linux 6.12

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a flaw in the u32 traffic control filter hash table handling. When a manual hash table is created with a specific handle in the 0x800..0xFFF range, the system fails to properly free or manage the IDR entry associated with it. This leads to a permanent leak of the entry and potential corruption of unrelated auto-allocated tables. The fix ensures that allocation and removal use a shared key domain to prevent handle aliasing and conflicts.

Detection Guidance

To detect this vulnerability, check for conflicting u32 filter handles in the 0x800..0xFFF range. Run: tc -d filter show dev <interface> ingress. Look for duplicate handles or unexpected table allocations. The vulnerability may cause manual tables to leak or alias with auto-allocated ones.

Impact Analysis

This vulnerability could allow an attacker to cause a denial of service by leaking system resources or corrupting traffic control filters. It may also enable unauthorized access to network traffic by misrouting packets to incorrect filter tables. Systems using traffic control with u32 filters are at risk, especially those with manual handle configurations in the vulnerable range.

Mitigation Strategies

Apply the Linux kernel patch resolving this issue. Avoid creating u32 filters with manual handles in the 0x800..0xFFF range until patched. Review existing filters for conflicts and remove any problematic entries.

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