Bug 2492387 (CVE-2026-52997)

Summary: CVE-2026-52997 kernel: net/sched: sch_dualpi2: drain both C-queue and L-queue in dualpi2_change()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's `sch_dualpi2` qdisc (queueing discipline) component. When `dualpi2_change()` attempts to enforce updated limit and memory limit values, it may incorrectly try to dequeue packets from an empty C-queue while packets are present in the L-queue. This can lead to a NULL skb (socket buffer) dereference, potentially causing a system crash or a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-06-24 18:09:17 UTC 
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.
Comment 1 Mauro Matteo Cascella 2026-06-26 15:31:11 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026062446-CVE-2026-52997-545a@gregkh/T