CVE-2024-56565 is a vulnerability identified in the Linux kernel's f2fs (Flash-Friendly File System) module, specifically related to the handling of discard commands on Logical Volume Manager (LVM) devices when snapshots are created. The vulnerability arises from improper management of discard operations after an LVM snapshot is created on a mounted f2fs filesystem. The root cause is that the kernel updates the discard_max_bytes parameter of the mounted LVM device to zero after snapshot creation. Subsequently, the function __submit_discard_cmd() passes a zero value for the number of sectors (@nr_sects) to __blkdev_issue_discard(), which returns a NULL bio pointer. This leads to a kernel panic, causing a denial of service (DoS) condition. The issue can be reproduced by creating an LVM volume, formatting it with f2fs, performing file operations, creating a snapshot of the logical volume, and then unmounting the filesystem. The patch to fix this vulnerability involves two key changes: first, dropping all remaining discard requests in the f2fs_unfreeze() function if an LVM snapshot has been created; second, adding a check for discard_max_bytes before submitting discard commands in __submit_discard_cmd(). This prevents the submission of invalid discard requests that would cause the kernel panic. The vulnerability affects Linux kernel versions containing the specified commit hashes and is relevant to systems using f2fs on LVM devices with snapshot functionality. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems running Linux with f2fs filesystems on LVM devices where snapshots are used. The impact is a potential denial of service due to kernel panic, which can cause system crashes and service interruptions. This can affect critical infrastructure, cloud service providers, and enterprises relying on Linux servers for storage and virtualization. The disruption could lead to downtime, data unavailability, and operational delays. Although the vulnerability does not directly lead to privilege escalation or data corruption, the DoS condition can be exploited by attackers with local access or by malicious insiders to disrupt services. Organizations with automated snapshot and backup processes using LVM on f2fs are particularly at risk. The lack of known exploits suggests limited immediate threat, but the vulnerability should be addressed promptly to prevent future exploitation. The impact on confidentiality and integrity is low, but availability impact is medium to high depending on the criticality of affected systems.

European organizations should take the following specific mitigation steps: 1) Apply the official Linux kernel patch that addresses this vulnerability as soon as it becomes available from trusted sources or Linux distribution vendors. 2) Review and audit systems using f2fs on LVM devices with snapshot capabilities to identify vulnerable kernel versions. 3) Temporarily avoid creating snapshots on LVM devices formatted with f2fs until patched, especially in production environments. 4) Implement monitoring for kernel panics and system crashes related to discard operations to detect potential exploitation attempts. 5) Harden access controls to limit local user access to systems where this vulnerability exists, reducing the risk of exploitation. 6) Test backup and snapshot workflows in controlled environments after patching to ensure stability. 7) Engage with Linux distribution security advisories and subscribe to vulnerability notifications to stay informed about updates. These measures go beyond generic advice by focusing on the specific interaction between f2fs, LVM snapshots, and discard commands.