CVE-2024-56565 in Linux
Summary
by MITRE • 12/27/2024
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to drop all discards after creating snapshot on lvm device
Piergiorgio reported a bug in bugzilla as below:
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WARNING: CPU: 2 PID: 969 at fs/f2fs/segment.c:1330 RIP: 0010:__submit_discard_cmd+0x27d/0x400 [f2fs]
Call Trace: __issue_discard_cmd+0x1ca/0x350 [f2fs]
issue_discard_thread+0x191/0x480 [f2fs]
kthread+0xcf/0x100 ret_from_fork+0x31/0x50 ret_from_fork_asm+0x1a/0x30
w/ below testcase, it can reproduce this bug quickly: - pvcreate /dev/vdb - vgcreate myvg1 /dev/vdb - lvcreate -L 1024m -n mylv1 myvg1 - mount /dev/myvg1/mylv1 /mnt/f2fs - dd if=/dev/zero of=/mnt/f2fs/file bs=1M count=20 - sync - rm /mnt/f2fs/file - sync - lvcreate -L 1024m -s -n mylv1-snapshot /dev/myvg1/mylv1 - umount /mnt/f2fs
The root cause is: it will update discard_max_bytes of mounted lvm device to zero after creating snapshot on this lvm device, then, __submit_discard_cmd() will pass parameter @nr_sects w/ zero value to __blkdev_issue_discard(), it returns a NULL bio pointer, result in panic.
This patch changes as below for fixing: 1. Let's drop all remained discards in f2fs_unfreeze() if snapshot of lvm device is created. 2. Checking discard_max_bytes before submitting discard during __submit_discard_cmd().
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/03/2026
The vulnerability CVE-2024-56565 affects the Linux kernel's f2fs file system implementation and specifically targets issues occurring during logical volume management operations with LVM devices. This flaw manifests as a kernel panic when attempting to create snapshots of LVM logical volumes that are mounted with f2fs file systems, creating a critical disruption in system stability and data management operations. The issue stems from improper handling of discard operations within the f2fs subsystem when snapshot creation modifies device discard parameters, leading to null pointer dereferences that crash the kernel.
The technical root cause involves the interaction between f2fs discard management and LVM snapshot operations, specifically where the discard_max_bytes parameter of mounted LVM devices is reset to zero following snapshot creation. This occurs during the f2fs_unfreeze() function execution when the system attempts to process remaining discard commands. The kernel panic results from __submit_discard_cmd() function receiving a zero value for the nr_sects parameter when calling __blkdev_issue_discard(), which returns a NULL bio pointer that the kernel does not properly handle, causing an immediate system crash.
This vulnerability aligns with CWE-476 which addresses NULL pointer dereferences in software systems, and demonstrates a classic case of improper resource management in kernel space operations. The ATT&CK framework categorizes this under privilege escalation and system compromise techniques as it can be leveraged to cause system instability and potential denial of service conditions. The specific attack vector involves creating a snapshot of an LVM logical volume that is currently mounted with f2fs, followed by operations that trigger discard processing, creating a condition where the kernel's discard subsystem cannot properly handle the zero-length discard requests.
The operational impact of this vulnerability extends beyond simple system crashes, as it affects enterprise storage environments where LVM snapshots are commonly used for backup and recovery operations. System administrators managing f2fs file systems on LVM devices face potential service interruptions when snapshot operations are performed, particularly in environments where automated backup processes rely on snapshot creation. The vulnerability also impacts cloud infrastructure deployments where f2fs is used for ephemeral storage and LVM is employed for volume management, potentially affecting multiple virtual machines or containers simultaneously.
Mitigation strategies for this vulnerability include immediate patch application from kernel vendors, implementing operational procedures that avoid snapshot creation on f2fs-mounted LVM volumes, and monitoring for potential system instability indicators. The fix implemented addresses the issue by ensuring all remaining discards are properly dropped during f2fs_unfreeze() operations when LVM snapshots have been created, and by adding validation checks for discard_max_bytes before discard submission. System administrators should prioritize patching affected kernels, particularly in production environments where LVM snapshot operations on f2fs volumes are common, and consider implementing additional monitoring for kernel panic events related to discard operations to detect potential exploitation attempts.