CVE-2026-97959

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 '