CVE-2024-26669 is a vulnerability identified in the Linux kernel's network scheduler (net/sched) subsystem, specifically affecting the 'flower' classifier used for flow offloading. The issue arises during the deletion of a queuing discipline (qdisc) from a network device. Normally, when a qdisc is deleted, the kernel stack instructs the underlying network driver to remove its flow offload callback from the associated filter block using the 'FLOW_BLOCK_UNBIND' command. Subsequently, the kernel iterates over the chains in the filter block and invokes the 'reoffload' operation of the classifier, which emits 'FLOW_CLS_DESTROY' commands to clean up filters. However, the vulnerability stems from the fact that this cleanup process does not extend to chain templates. As a result, the underlying driver never receives the 'FLOW_CLS_TMPLT_DESTROY' command when a qdisc is deleted, causing a memory leak due to unreleased chain template objects. This leak can accumulate over time, potentially leading to resource exhaustion. The root cause is linked to a commit that reordered the calls to tcf_block_offload_unbind() and tcf_block_flush_all_chains() in the __tcf_block_put() function, which changed the cleanup sequence. Reversing this order is not feasible because the filter block must be freed only after flushing all chains. The fix involves introducing a new 'tmplt_reoffload' operation that the kernel stack invokes during the replay process, ensuring that the 'FLOW_CLS_TMPLT_DESTROY' command is sent appropriately. This operation has been implemented in the flower classifier, which is the sole classifier supporting chain templates. Exploitation requires the ability to manipulate qdiscs and flow offload configurations on a Linux system, typically achievable by users with administrative privileges or through compromised systems. The vulnerability does not directly lead to code execution or privilege escalation but can cause memory leaks that degrade system stability and performance over time, potentially leading to denial of service (DoS) conditions. There are no known exploits in the wild at this time.

For European organizations, this vulnerability primarily poses a risk to network infrastructure stability and availability. Linux is widely deployed across servers, network appliances, and embedded devices in Europe, including critical infrastructure, telecommunications, and enterprise environments. Systems that utilize advanced traffic control features with the flower classifier for flow offloading are particularly susceptible. The memory leak can lead to gradual resource exhaustion, causing network devices or servers to become unresponsive or crash, resulting in service disruptions. In environments with high network traffic and frequent qdisc modifications, the impact could be more pronounced. Although the vulnerability does not directly compromise confidentiality or integrity, the resulting denial of service could affect business continuity, especially for organizations relying on Linux-based networking equipment or virtualized network functions. The absence of known exploits reduces immediate risk, but unpatched systems remain vulnerable to potential future exploitation or accidental resource depletion.

1. Apply the official Linux kernel patches that introduce the 'tmplt_reoffload' operation and fix the chain template offload cleanup process as soon as they become available from trusted Linux distributions or kernel maintainers. 2. Monitor and audit network device configurations, especially qdisc and flow offload settings, to detect unusual or frequent changes that could exacerbate the memory leak. 3. Limit administrative access to network configuration interfaces to trusted personnel and enforce strict privilege controls to prevent unauthorized manipulation of qdiscs. 4. Implement resource monitoring on critical Linux systems to track memory usage trends and detect anomalies indicative of leaks. 5. Consider temporarily disabling or avoiding the use of chain templates and flower classifier offloading features in environments where stability is critical until patches are applied. 6. Maintain up-to-date backups and incident response plans to quickly recover from potential service disruptions caused by this vulnerability. 7. Engage with Linux distribution vendors and network hardware providers to ensure timely updates and guidance specific to affected products.