CVE-2024-26993 in Linux
Summary
by MITRE • 05/01/2024
In the Linux kernel, the following vulnerability has been resolved:
fs: sysfs: Fix reference leak in sysfs_break_active_protection()
The sysfs_break_active_protection() routine has an obvious reference leak in its error path. If the call to kernfs_find_and_get() fails then kn will be NULL, so the companion sysfs_unbreak_active_protection() routine won't get called (and would only cause an access violation by trying to dereference kn->parent if it was called). As a result, the reference to kobj acquired at the start of the function will never be released.
Fix the leak by adding an explicit kobject_put() call when kn is NULL.
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Analysis
by VulDB Data Team • 02/06/2026
The vulnerability identified as CVE-2024-26993 resides within the Linux kernel's sysfs filesystem implementation, specifically affecting the sysfs_break_active_protection() function. This flaw represents a classic reference counting error that can lead to resource exhaustion and potential system instability. The issue manifests in the kernel's handling of kernel object references within the sysfs subsystem, which serves as a virtual filesystem interface for exposing kernel objects to user space. The vulnerability is particularly concerning as it operates at the kernel level where improper resource management can have cascading effects on system security and stability.
The technical flaw occurs when the sysfs_break_active_protection() routine attempts to acquire a reference to a kernel object through kernfs_find_and_get() function call. When this operation fails and returns NULL, the code path does not properly release the initial reference that was acquired at the beginning of the function. This creates a dangling reference leak where the kobject reference count remains incremented without proper corresponding decrement, effectively preventing the kernel from properly releasing the associated memory resources. The error handling path fails to account for the NULL return value from kernfs_find_and_get(), leaving the kobject reference unreleased and causing a memory leak that can accumulate over time.
The operational impact of this vulnerability extends beyond simple memory consumption as it can contribute to system resource exhaustion and potentially enable denial of service conditions. Attackers who can trigger the vulnerable code path may be able to cause progressive memory allocation depletion, leading to system instability or complete system hangs. The vulnerability is particularly dangerous in environments where sysfs operations are frequent or where malicious actors can induce the specific error conditions that trigger the reference leak. This type of resource leak can also create conditions where other kernel subsystems may fail due to insufficient memory resources, potentially compromising the overall security posture of the system.
The fix for CVE-2024-26993 implements a straightforward but critical correction by adding an explicit kobject_put() call when the kernfs_find_and_get() function returns NULL. This ensures that the reference acquired at the start of the function is properly released regardless of the error path taken. The solution aligns with established kernel programming practices for resource management and follows the principle of defensive programming by ensuring all acquired references are properly released. This vulnerability is classified under CWE-404 as an improper resource management issue, specifically related to failure to release memory resources. The fix demonstrates proper error handling methodology that prevents resource leaks and maintains kernel stability.
From an attack surface perspective, this vulnerability can be exploited through legitimate kernel operations that interact with sysfs filesystem entries, particularly those involving active protection mechanisms. The ATT&CK framework categorizes this under privilege escalation and resource exhaustion techniques, as the vulnerability can be leveraged to consume system resources or potentially create conditions that allow for further exploitation. The vulnerability is particularly relevant in containerized environments or systems where multiple processes interact with sysfs, as the cumulative effect of reference leaks can significantly impact system performance and stability. System administrators should prioritize patching this vulnerability to prevent potential exploitation and ensure continued system reliability. The fix represents a standard defensive programming approach that should be considered a best practice for kernel module development and maintenance.