CVE-2024-43856: Linux Kernel Race Condition Vulnerability

CVE-2024-43856 Overview

CVE-2024-43856 is a race condition vulnerability in the Linux kernel's Direct Memory Access (DMA) subsystem. The flaw resides in the dmam_free_coherent() function, which manages DMA coherent memory allocations tracked through the device resource management (devres) framework. Due to an incorrect ordering of operations, a concurrent task can allocate memory with the same virtual address before the original entry is removed from the devres list. This creates duplicate devres entries that trigger a WARN_ON() in dmam_match and can lead to the wrong entry being freed. The issue is classified under [CWE-770] (Allocation of Resources Without Limits or Throttling) and affects multiple Linux kernel versions.

Critical Impact
A local low-privileged attacker can trigger kernel state corruption and denial of service through a race condition in DMA coherent memory deallocation.

Affected Products

Linux Kernel (multiple versions prior to fixed commits)
Debian distributions (addressed in LTS advisories)
Siemens products incorporating affected Linux kernel versions

Discovery Timeline

2024-08-17 - CVE-2024-43856 published to NVD
2024-10 - Debian LTS security advisory published
2025-01 - Additional Debian LTS security advisory published
2026-05-12 - Last updated in NVD database

Technical Details for CVE-2024-43856

Vulnerability Analysis

The vulnerability stems from incorrect operation ordering in the dmam_free_coherent() function within the Linux kernel's DMA management code. The function originally performs two operations sequentially: it first frees the DMA allocation, then calls devres_destroy() to remove the tracking data structure from the device resource list. This window between the two calls creates a race condition.

During this window, a concurrent task on another CPU can request a new DMA allocation and receive the same virtual address that was just freed. The new allocation gets added to the devres list before devres_destroy() runs on the original entry. The result is two devres entries sharing the same vaddr, and devres_destroy() may then free the wrong entry. This triggers the WARN_ON() assertion in dmam_match, indicating kernel state corruption.

Root Cause

The root cause is improper sequencing between resource deallocation and resource tracking metadata removal. The kernel released the DMA buffer back to the allocator pool before it removed the devres tracking entry, violating the invariant that the devres list should not contain entries pointing to memory available for reuse.

Attack Vector

Exploitation requires local access with low privileges. An attacker capable of triggering rapid concurrent DMA coherent allocation and deallocation operations on a vulnerable driver path can race the dmam_free_coherent() call. Successful exploitation causes kernel warnings, potential incorrect deallocation of legitimate devres entries, and availability impact through kernel instability or panic on systems configured with panic_on_warn.

The fix reorders the operations so devres_destroy() is called before the DMA allocation is freed, closing the race window. See the upstream patches such as Kernel Change 87b34c8c and Kernel Change f993a4ba for the corrected sequence.

Detection Methods for CVE-2024-43856

Indicators of Compromise

Kernel log entries containing WARN_ON traces originating from dmam_match or related devres functions
Unexpected kernel warnings during DMA-heavy workloads on drivers using dmam_alloc_coherent and dmam_free_coherent
Kernel panics on systems with panic_on_warn=1 triggered during device driver operations

Detection Strategies

Audit installed kernel versions across Linux endpoints and compare against the fixed commits referenced in the stable kernel tree
Monitor dmesg and /var/log/kern.log for warnings emitted from the DMA devres subsystem
Correlate kernel warnings with processes performing repeated DMA allocation cycles to identify potential exploitation attempts

Monitoring Recommendations

Centralize Linux kernel logs in a security data lake to identify recurring WARN_ON events across the fleet
Track patch compliance for the Linux kernel against vendor advisories such as the Debian LTS Announcement October 2024 and Siemens Security Advisory SSA-265688
Alert on unprivileged users running workloads that generate abnormal volumes of DMA-related kernel messages

How to Mitigate CVE-2024-43856

Immediate Actions Required

Identify all Linux systems running kernel versions prior to the fixed commits and prioritize patching
Apply distribution-provided kernel updates from Debian, Siemens, and other affected vendors
Restrict local access to multi-user systems while patching is in progress, as the attack vector is local

Patch Information

The Linux kernel maintainers have merged the fix across multiple stable branches. Reference the following commits for the patched code: 1fe97f68, 22094f5f, 25719308, 28e8b740, 2f7bbdc7, 87b34c8c, f993a4ba, and fe2d2460. Distribution-level updates are available through the Debian LTS Announcement January 2025 and Siemens Security Advisory SSA-265688.

Workarounds

No official workaround exists. Apply the vendor-supplied kernel patches as the primary remediation.
Limit local shell access and reduce the number of unprivileged users on affected hosts until patches are deployed
Disable panic_on_warn where operationally acceptable to prevent the warning from escalating to a system panic

bash

# Verify kernel version and check for the fix
uname -r
apt list --installed 2>/dev/null | grep linux-image

# Apply distribution updates (Debian/Ubuntu example)
sudo apt update && sudo apt upgrade linux-image-$(uname -r | sed 's/[^-]*-[^-]*-//')
sudo reboot