In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_route: free emptied bucket on filter move
route4_change can move an existing filter to a different top-level
bucket: route4_set_parms recomputes the handle from TCA_ROUTE4_TO/
FROM/IIF, and the handle-mismatch check is gated on the 'new' flag, so
for an existing filter the new handle may differ from the old one and
land in a different bucket. When this happens, the filter is unlinked
from the old bucket, but the bucket itself is never freed once it goes
empty. The stale empty bucket remains in head->table[], causing
route4_delete to report *last=false even after the last live filter is
gone. That pins the empty tcf_proto and causes a leak.
Fix this by refcounting the filters linked to a bucket and freeing the
bucket when the count drops to zero. The existing scan in route4_delete
goes away with it.
The count is updated at all sites that link or unlink a filter during add,
change and delete, and the bucket is dropped from head->table[] as soon as
it reaches zero.
Conditions to recreate the bug:
CONFIG_NET_CLS_ROUTE4=y, CONFIG_NET_SCH_INGRESS=y, CONFIG_NET_CLS_ACT=y.
tc qdisc replace dev lo clsact
tc filter add dev lo ingress protocol ip pref 100 route from 1 to 1
tc filter change dev lo ingress protocol ip pref 100 handle 0x10001 \
route from 1 to 2
tc filter del dev lo ingress protocol ip pref 100 handle 0x10002 \
route from 1 to 2
tc filter show dev lo ingress | grep -c 'pref 100 route chain 0 '
net/sched: cls_route: free emptied bucket on filter move
route4_change can move an existing filter to a different top-level
bucket: route4_set_parms recomputes the handle from TCA_ROUTE4_TO/
FROM/IIF, and the handle-mismatch check is gated on the 'new' flag, so
for an existing filter the new handle may differ from the old one and
land in a different bucket. When this happens, the filter is unlinked
from the old bucket, but the bucket itself is never freed once it goes
empty. The stale empty bucket remains in head->table[], causing
route4_delete to report *last=false even after the last live filter is
gone. That pins the empty tcf_proto and causes a leak.
Fix this by refcounting the filters linked to a bucket and freeing the
bucket when the count drops to zero. The existing scan in route4_delete
goes away with it.
The count is updated at all sites that link or unlink a filter during add,
change and delete, and the bucket is dropped from head->table[] as soon as
it reaches zero.
Conditions to recreate the bug:
CONFIG_NET_CLS_ROUTE4=y, CONFIG_NET_SCH_INGRESS=y, CONFIG_NET_CLS_ACT=y.
tc qdisc replace dev lo clsact
tc filter add dev lo ingress protocol ip pref 100 route from 1 to 1
tc filter change dev lo ingress protocol ip pref 100 handle 0x10001 \
route from 1 to 2
tc filter del dev lo ingress protocol ip pref 100 handle 0x10002 \
route from 1 to 2
tc filter show dev lo ingress | grep -c 'pref 100 route chain 0 '
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||||||||
| Linux | Linux | affected |
|
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Advisories
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Fixes
Solution
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Workaround
No workaround given by the vendor.
References
History
Fri, 25 Sep 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_route: free emptied bucket on filter move route4_change can move an existing filter to a different top-level bucket: route4_set_parms recomputes the handle from TCA_ROUTE4_TO/ FROM/IIF, and the handle-mismatch check is gated on the 'new' flag, so for an existing filter the new handle may differ from the old one and land in a different bucket. When this happens, the filter is unlinked from the old bucket, but the bucket itself is never freed once it goes empty. The stale empty bucket remains in head->table[], causing route4_delete to report *last=false even after the last live filter is gone. That pins the empty tcf_proto and causes a leak. Fix this by refcounting the filters linked to a bucket and freeing the bucket when the count drops to zero. The existing scan in route4_delete goes away with it. The count is updated at all sites that link or unlink a filter during add, change and delete, and the bucket is dropped from head->table[] as soon as it reaches zero. Conditions to recreate the bug: CONFIG_NET_CLS_ROUTE4=y, CONFIG_NET_SCH_INGRESS=y, CONFIG_NET_CLS_ACT=y. tc qdisc replace dev lo clsact tc filter add dev lo ingress protocol ip pref 100 route from 1 to 1 tc filter change dev lo ingress protocol ip pref 100 handle 0x10001 \ route from 1 to 2 tc filter del dev lo ingress protocol ip pref 100 handle 0x10002 \ route from 1 to 2 tc filter show dev lo ingress | grep -c 'pref 100 route chain 0 ' | |
| Title | net/sched: cls_route: free emptied bucket on filter move | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-25T10:23:04.348Z
Reserved: 2026-09-25T10:18:58.205Z
Link: CVE-2026-97959
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-25T11:17:23.600
Modified: 2026-09-25T11:17:23.600
Link: CVE-2026-97959
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.