CVE-2026-74700

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_api: Always acquire rtnl_lock when destroying locked classifiers

Another challenge with unlocked filters.

There is a short window in tc_new_tfilter where a tcf_proto can be found

and briefly referenced by a totally unrelated, unlocked classifier's request

and cause a race.

Feng created a poc which created this race with two threads, one creating a

u32 filter and other a flower filter in the same chain/prio:

1. Both threads enter tc_new_tfilter, both find the chain empty, both

drop filter_chain_lock

2. u32 finishes tcf_proto_create("u32") first, calls

tcf_chain_tp_insert_unique() -> inserts u32_tp into the chain

3. flower finishes tcf_proto_create("flower") later, calls

tcf_chain_tp_insert_unique() -> tcf_chain_tp_find() now sees u32_tp

already there, takes a reference on it, destroys flower's own tp_new

and returns u32_tp to the caller.

Flower then hits the kind mismatch check (becaus

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References