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.
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.
Published:
2026-10-18
Score:
n/a
EPSS:
n/a
KEV:
No
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||||||||||||||
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| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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No data.
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No data available yet.
Remediation
No solution or workaround provided in the CVE record.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
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References
History
Sun, 18 Oct 2026 15:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | net/sched: cls_u32: fix manual hash table handle IDR aliasing | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-18T15:19:50.589Z
Reserved: 2026-09-25T10:25:14.361Z
Link: CVE-2026-98629
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.