CVE-2024-53044 is a vulnerability in the Linux kernel's network scheduling subsystem, specifically within the traffic control (tc) block API. The issue arises in the function tcf_block_get_ext(), which manages flow blocks for ingress and egress traffic control on network devices. When a user attempts to assign the same block index to both ingress and egress blocks on a device (e.g., using the command `tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact`), the operation fails with an error indicating the flow block control block (cb) is busy. This failure is due to the underlying implementation inserting the device twice into a shared xarray structure, which is not allowed. More critically, when the insertion fails, the code emits a FLOW_BLOCK_BIND command to the offload driver but does not issue a corresponding FLOW_BLOCK_UNBIND command, leaving the offload driver in an inconsistent state. This results in the flow block remaining bound and busy, preventing further configuration changes or removal of the block without rebooting the system or unbinding and rebinding the network device driver. The root cause is a missing error teardown path in the kernel code, which was introduced during code refactoring. The fix involves ensuring that when xa_insert() fails, the kernel properly calls tcf_block_offload_unbind() to clean up the offload state. This vulnerability affects Linux kernel versions containing the commit identified by hash 94e2557d086ad831027c54bc9c2130d337c72814 and likely later versions until patched. The issue does not appear to have known exploits in the wild as of now and does not have an assigned CVSS score. The vulnerability primarily impacts network administrators and systems relying on advanced traffic control configurations, especially those using clsact qdiscs with ingress and egress blocks on network interfaces.

For European organizations, this vulnerability can cause significant operational disruptions in network infrastructure. Systems running affected Linux kernels that utilize traffic control features for network performance, security filtering, or traffic shaping may experience irrecoverable failures in network device configuration after triggering this bug. The inability to recover without a system reboot or driver rebind can lead to downtime, impacting critical services such as data centers, cloud providers, telecom infrastructure, and enterprise networks. This is particularly relevant for organizations that rely on Linux-based routers, firewalls, or network appliances. While the vulnerability does not directly enable remote code execution or privilege escalation, the denial of service effect on network devices can degrade availability and potentially interrupt business-critical communications. Additionally, recovery procedures requiring reboots or manual driver operations may increase operational costs and risk during incident response. Since the vulnerability is triggered by specific user-space commands, it may also be exploited by malicious insiders or attackers with local access to network management interfaces, emphasizing the need for strict access controls.

1. Apply the official Linux kernel patches that address CVE-2024-53044 as soon as they become available. Monitor kernel mailing lists and vendor advisories for updates. 2. Until patched, avoid configuring ingress and egress blocks with the same block index on the same network interface using the tc tool. 3. Implement strict access controls and auditing on systems that allow traffic control configuration to prevent unauthorized or accidental triggering of the vulnerability. 4. For critical systems, consider deploying network device driver reload scripts or automation to quickly unbind and rebind network drivers as a temporary recovery measure without full system reboots. 5. Maintain robust backup and recovery procedures to minimize downtime in case of system reboots. 6. Monitor system logs for error messages related to 'Flow block cb is busy' to detect attempts to trigger this issue. 7. Engage with Linux distribution vendors to obtain backported patches if using long-term support kernels. 8. Test traffic control configurations in staging environments before deployment to detect potential issues related to this vulnerability.