CVE-2025-68325

/// Technical description

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

net/sched: sch_cake: Fix incorrect qlen reduction in cake_drop

In cake_drop(), qdisc_tree_reduce_backlog() is used to update the qlen

and backlog of the qdisc hierarchy. Its caller, cake_enqueue(), assumes

that the parent qdisc will enqueue the current packet. However, this

assumption breaks when cake_enqueue() returns NET_XMIT_CN: the parent

qdisc stops enqueuing current packet, leaving the tree qlen/backlog

accounting inconsistent. This mismatch can lead to a NULL dereference

(e.g., when the parent Qdisc is qfq_qdisc).

This patch computes the qlen/backlog delta in a more robust way by

observing the difference before and after the series of cake_drop()

calls, and then compensates the qdisc tree accounting if cake_enqueue()

returns NET_XMIT_CN.

To ensure correct compensation when ACK thinning is enabled, a new

variable is introduced to keep qlen unchanged.

/// 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