CVE-2026-52997net/sched: sch_dualpi2: drain both C-queue and L-queue in dualpi2_change()

Official description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_dualpi2: drain both C-queue and L-queue in dualpi2_change() Fix dualpi2_change() to correctly enforce updated limit and memlimit values after a configuration change of the dualpi2 qdisc. Before this patch, dualpi2_change() always attempted to dequeue packets via the root qdisc (C-queue) when reducing backlog or memory usage, and unconditionally assumed that a valid skb will be returned. When traffic classification results in packets being queued in the L-queue while the C-queue is empty, this leads to a NULL skb dereference during limit or memlimit enforcement. This is fixed by first dequeuing from the C-queue path if it is non-empty. Once the C-queue is empty, packets are dequeued directly from the L-queue. Return values from qdisc_dequeue_internal() are checked for both queues. When dequeuing from the L-queue, the parent qdisc qlen and backlog counters are updated explicitly to keep overall qdisc statistics consistent.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/86cf2eba2056bcf9c41fba260e599bd95bf9943b
• https://git.kernel.org/stable/c/3042add80c2c50bd127d570b83319af612efde65
• https://git.kernel.org/stable/c/478ed6b7d2577439c610f91fa8759a4c878a4264