In the Linux kernel, the following vulnerability has been resolved: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 \ htb rate 64bit tc qdisc add dev lo parent 1:1 handle f: \ cake memlimit 1b ping -I lo -f -c1 -s64 -W0.001 127.0.0.1 This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow. I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.
Upstream advisory: https://lore.kernel.org/linux-cve-announce/2025091144-CVE-2025-39766-7465@gregkh/T
This issue has been addressed in the following products: Red Hat Enterprise Linux 9 Via RHSA-2026:8921 https://access.redhat.com/errata/RHSA-2026:8921
This issue has been addressed in the following products: Red Hat Enterprise Linux 10 Via RHSA-2026:9264 https://access.redhat.com/errata/RHSA-2026:9264