CVE-2024-38554 in Linux
Summary
by MITRE • 06/19/2024
In the Linux kernel, the following vulnerability has been resolved:
ax25: Fix reference count leak issue of net_device
There is a reference count leak issue of the object "net_device" in ax25_dev_device_down(). When the ax25 device is shutting down, the ax25_dev_device_down() drops the reference count of net_device one or zero times depending on if we goto unlock_put or not, which will cause memory leak.
In order to solve the above issue, decrease the reference count of net_device after dev->ax25_ptr is set to null.
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Analysis
by VulDB Data Team • 10/04/2025
The vulnerability described in CVE-2024-38554 represents a critical reference count management flaw within the Linux kernel's AX.25 networking subsystem. This issue specifically affects the ax25_dev_device_down() function which handles the shutdown process of AX.25 network devices. The problem manifests as a memory leak that occurs when the reference count of net_device objects is not properly decremented during device shutdown operations. The flaw stems from conditional execution paths within the function where the reference count is only reduced in certain code branches, leaving the reference count in an inconsistent state. This improper reference count handling creates a scenario where net_device objects remain allocated in memory even after they should be freed, leading to gradual memory exhaustion over time.
The technical implementation of this vulnerability involves the AX.25 protocol stack within the Linux kernel networking subsystem, which implements the Amateur Radio AX.25 protocol for packet radio communications. The ax25_dev_device_down() function is responsible for cleaning up AX.25 device resources when a device goes down, but the reference counting logic contains a race condition or control flow issue. When the function executes, it attempts to manage the reference count of net_device structures through conditional goto statements that determine whether to decrement the reference count. However, the logic does not guarantee that the reference count will be decremented in all execution paths, causing the reference count to remain artificially high and preventing proper memory deallocation.
This memory leak vulnerability directly impacts system stability and resource management capabilities, particularly in embedded systems or network equipment that heavily utilize AX.25 protocols. The operational consequences include progressive memory consumption that can lead to system performance degradation, eventual system crashes, or denial of service conditions when the kernel's memory pool becomes exhausted. The vulnerability is particularly concerning because it operates at the kernel level where memory management errors can have cascading effects on system operations. The issue affects systems running Linux kernels that implement AX.25 networking support, potentially impacting various networking equipment including amateur radio systems, satellite communications, and specialized network infrastructure that relies on AX.25 protocol implementations.
The fix for this vulnerability involves repositioning the reference count decrement operation to occur after the ax25_ptr is set to null, ensuring that the reference count is properly managed regardless of execution path taken. This remediation aligns with standard kernel memory management practices and follows the principle of ensuring resource cleanup occurs in a predictable and consistent manner. The solution addresses the core issue identified in CWE-404, which deals with improper resource management and memory leaks in software systems. From an ATT&CK perspective, this vulnerability could be leveraged in resource exhaustion attacks, potentially falling under the T1499.004 technique for network denial of service through resource consumption. The mitigation strategy requires kernel updates and proper patch management to ensure all affected systems receive the reference count management fix. System administrators should prioritize applying this patch, particularly in environments where AX.25 networking is actively used or where memory conservation is critical for system stability and performance.