CVE-2026-52997
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.
Summary dbcve.org
In the Linux kernel's sch_dualpi2 qdisc, dualpi2_change() incorrectly assumes packets always exist in the C-queue when enforcing updated limit or memlimit values. When traffic classification results in packets queued in the L-queue while the C-queue is empty, the function attempts to dereference a NULL skb, causing a kernel NULL pointer dereference vulnerability.
Mitigation
Apply the upstream kernel patch which fixes the dequeue logic to check C-queue first, then L-queue if empty, with proper return value validation. Alternatively, update to a kernel version containing this fix.