CVE-2024-42314: Linux Kernel Use-After-Free Vulnerability

CVE-2024-42314 Overview

CVE-2024-42314 is a use-after-free vulnerability discovered in the Linux kernel's Btrfs filesystem implementation. The flaw exists in the add_ra_bio_pages() function where an extent map is accessed to calculate the add_size value after the reference to that extent map has already been dropped. This memory safety violation can lead to unpredictable behavior including potential privilege escalation, information disclosure, or system crashes.

Critical Impact

Local attackers with low privileges can exploit this use-after-free condition in the Btrfs compressed bio handling to potentially achieve arbitrary code execution or cause denial of service on affected Linux systems.

Affected Products

• Linux Kernel (multiple versions with Btrfs filesystem support)
• Systems using Btrfs compressed read-ahead functionality
• Debian-based distributions (security advisory issued)

Discovery Timeline

• August 17, 2024 - CVE-2024-42314 published to NVD
• November 03, 2025 - Last updated in NVD database

Technical Details for CVE-2024-42314

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue that occurs when a program continues to use a pointer after it has been freed. In the context of the Linux kernel's Btrfs filesystem, the add_ra_bio_pages() function is responsible for adding pages during compressed bio read-ahead operations.

The vulnerable code path involves extent map management during compressed data handling. Extent maps in Btrfs are data structures that track the mapping between logical file offsets and physical disk locations. When processing compressed bios, the kernel needs to reference these extent maps to determine the size of data to be added.

The flaw manifests because the code calculates add_size by accessing extent map properties after the reference count on the extent map has been decremented. If the reference count reaches zero, the extent map memory may be freed, leading to access of deallocated memory. This creates a race condition where the memory could be reallocated for other purposes, resulting in corrupted data or exploitable conditions.

Root Cause

The root cause of CVE-2024-42314 is improper lifetime management of the extent map object in the add_ra_bio_pages() function. The code drops its reference to the extent map before completing all operations that require access to the extent map's data. Specifically, the add_size calculation depends on extent map values, but this calculation occurs after the free_extent_map() call that releases the reference.

This is a classic use-after-free pattern where:

1. A reference to a shared object (extent map) is acquired
2. The reference is released prematurely
3. The object is then accessed again, potentially after deallocation

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have low-privileged access to the system. Exploitation would involve:

1. Creating or accessing compressed files on a Btrfs filesystem to trigger the add_ra_bio_pages() code path
2. Manipulating timing or memory allocation patterns to increase the likelihood of accessing freed memory
3. Potentially leveraging heap spray techniques to control the contents of reallocated memory

The fix involves computing the add_size value before dropping the extent map reference, ensuring all necessary data is captured while the object is still valid. The remediation commits show that developers moved the size calculation to occur prior to releasing the extent map reference.

For technical details on the patch implementation, see the Kernel Git Commit Patch.

Detection Methods for CVE-2024-42314

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing Btrfs or extent map functions
• System crashes during compressed file read operations on Btrfs volumes
• Memory corruption errors in kernel logs related to add_ra_bio_pages() or extent_map structures
• Unusual process behavior following Btrfs file access operations

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for use-after-free warnings or Btrfs-related errors
• Deploy kernel debugging tools such as KASAN (Kernel Address Sanitizer) to detect memory safety violations
• Implement file integrity monitoring on critical Btrfs filesystems to detect unexpected modifications
• Use SentinelOne's Linux agent to monitor for exploitation attempts targeting kernel vulnerabilities

Monitoring Recommendations

• Enable kernel crash dump analysis to capture forensic data from any exploitation attempts
• Configure audit rules to log access patterns to Btrfs compressed files on sensitive systems
• Deploy endpoint detection and response (EDR) solutions capable of monitoring kernel-level operations
• Review system stability metrics for anomalies that may indicate exploitation attempts

How to Mitigate CVE-2024-42314

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the fix for this vulnerability
• Review systems using Btrfs filesystems and prioritize patching based on exposure
• Consider temporarily disabling Btrfs compression on critical systems if immediate patching is not possible
• Monitor affected systems for signs of exploitation while patches are being applied

Patch Information

Patches for CVE-2024-42314 have been released through the Linux kernel stable branches. The fix reorders operations in add_ra_bio_pages() to compute add_size before dropping the extent map reference. Multiple kernel commits address this issue:

• Kernel Git Commit Update
• Kernel Git Commit Fix
• Kernel Git Commit Improvement

Debian has also issued a security announcement for affected distributions. See the Debian LTS Announcement for distribution-specific guidance.

Workarounds

• If patching is not immediately possible, consider remounting Btrfs filesystems without compression enabled
• Restrict local user access on systems where Btrfs is used for critical data
• Implement additional monitoring on systems that cannot be immediately patched
• Consider migrating critical workloads to non-Btrfs filesystems temporarily until patches are applied

# Check current kernel version
uname -r

# List Btrfs filesystems and their compression settings
btrfs filesystem show
mount | grep btrfs

# Update kernel on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade linux-image-$(uname -r)

# Reboot to apply kernel update
sudo reboot