CVE-2024-57979 is a high-severity use-after-free vulnerability in the Linux kernel's Pulse Per Second (PPS) subsystem, specifically related to the handling of character devices (cdev) embedded within pps_device structures. The flaw arises because the pps_device_destruct() function frees the pps_device containing the embedded cdev immediately after calling cdev_del(). However, as documented in the kernel source, file operations (fops) for previously opened cdevs remain callable even after cdev_del() returns. This leads to a use-after-free condition when these stale fops are invoked, causing kernel memory corruption, refcount underflows, and potentially kernel panics or system crashes. The vulnerability was observed on a Raspberry Pi 4 running ntpd and gpsd, where rebooting triggered consistent kernel warnings and panics due to this bug. The root cause is that the embedded cdev is freed prematurely, and the fix involved removing the embedded cdev and switching to __register_chrdev() with pps_idr as the authoritative source for device minor numbers. This change ensures that the pps->dev reference count remains valid while userspace can still access the device, preventing premature freeing. The vulnerability affects multiple Linux kernel versions prior to the patch commit d953e0e837e6 and is classified under CWE-416 (Use After Free). The CVSS v3.1 score is 7.8 (High), reflecting the local attack vector, low complexity, low privileges required, no user interaction, and high impact on confidentiality, integrity, and availability. No known exploits are currently reported in the wild. This vulnerability impacts systems using the PPS subsystem, commonly employed in precise time synchronization setups involving GPS devices and ntpd/gpsd services.

For European organizations, this vulnerability poses a significant risk especially to infrastructure relying on precise time synchronization, such as telecommunications, financial trading platforms, scientific research facilities, and industrial control systems. The use-after-free can lead to kernel crashes, denial of service, and potentially privilege escalation if exploited in conjunction with other vulnerabilities. Systems running Linux kernels with affected versions and utilizing PPS devices for GPS-based timing are at risk. Disruptions in time synchronization can cascade into operational failures, data integrity issues, and compliance violations, particularly in sectors with strict timing requirements like finance and critical infrastructure. Given the vulnerability requires local privileges but no user interaction, insider threats or compromised accounts could exploit this to destabilize systems. The lack of known exploits reduces immediate threat but the high impact and kernel-level nature warrant urgent patching to prevent future exploitation.

1. Apply the official Linux kernel patches that remove the embedded cdev and implement the pps_idr-based device registration as described in commit d953e0e837e6 or later stable kernel releases. 2. For organizations unable to immediately patch, consider disabling the PPS subsystem if not required or isolating systems that use GPSd/ntpd with PPS to minimize exposure. 3. Monitor kernel logs for signs of use-after-free warnings, refcount underflows, or kernel panics related to pps devices to detect potential exploitation attempts or instability. 4. Implement strict access controls and auditing on systems running PPS to limit local user privileges and detect suspicious activity. 5. Coordinate with hardware vendors and Linux distribution maintainers to ensure timely deployment of patched kernels across all affected devices, including embedded systems like Raspberry Pi-based deployments. 6. For critical environments, conduct thorough testing of patched kernels to ensure stability and compatibility with existing time synchronization infrastructure before wide deployment.