CVE-2025-22016 in Linux
Summary
by MITRE • 04/08/2025
In the Linux kernel, the following vulnerability has been resolved:
dpll: fix xa_alloc_cyclic() error handling
In case of returning 1 from xa_alloc_cyclic() (wrapping) ERR_PTR(1) will be returned, which will cause IS_ERR() to be false. Which can lead to dereference not allocated pointer (pin).
Fix it by checking if err is lower than zero.
This wasn't found in real usecase, only noticed. Credit to Pierre.
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Analysis
by VulDB Data Team • 10/28/2025
The vulnerability CVE-2025-22016 addresses a critical error handling flaw in the Linux kernel's digital phase-locked loop subsystem, specifically within the dpll module. This issue manifests in the xa_alloc_cyclic() function which is responsible for cyclic allocation of memory addresses within the kernel's memory management system. The flaw occurs when the function returns a value of 1 indicating a wraparound condition, which should be treated as an error condition but is incorrectly handled due to flawed error checking logic. The vulnerability stems from the improper interpretation of the return value where ERR_PTR(1) is returned but IS_ERR() macro evaluates to false, creating a scenario where subsequent code attempts to dereference a pointer that was never properly allocated. This represents a classic case of incorrect error propagation and handling that can lead to system instability and potential security implications. The flaw is particularly concerning as it exists in kernel space where improper memory management can result in privilege escalation or system crashes, making it a significant concern for embedded systems and server environments that rely heavily on precise timing and synchronization mechanisms.
The technical implementation of this vulnerability involves the interaction between the xa_alloc_cyclic() function and the error handling mechanisms within the Linux kernel's memory management subsystem. When the cyclic allocation reaches its maximum value and wraps around, the function returns a value that should signal an error condition through ERR_PTR(1), but the subsequent IS_ERR() check fails to properly identify this as an error due to the specific value interpretation. This causes the calling code to proceed with what it believes is a valid pointer, but which is actually a corrupted or uninitialized memory reference pointing to the pin variable. The flaw is rooted in the fundamental assumption that error codes returned from kernel functions will be properly handled by the standard error checking macros, which in this case fails due to the specific return value of 1 that is treated as a valid pointer rather than an error indicator. This misclassification creates a path where memory safety mechanisms are bypassed, leading to potential memory corruption or access violations that could be exploited by malicious actors.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation and denial of service conditions within kernel space operations. When the dpll subsystem manages timing and synchronization for critical hardware components, such as network interfaces or storage controllers, improper error handling can cause cascading failures that affect system reliability and security. The vulnerability is particularly dangerous in embedded systems or real-time applications where precise timing is crucial, as incorrect pointer handling could lead to hardware malfunctions or data corruption. Additionally, this flaw could be leveraged in privilege escalation attacks if an attacker can control the conditions that trigger the wraparound scenario, potentially allowing them to execute arbitrary code in kernel space. The lack of a real-world exploitation case does not diminish the severity, as the underlying memory safety issue remains present and could be triggered by specific sequences of operations or system states.
Mitigation strategies for CVE-2025-22016 should focus on immediate kernel updates that implement the corrected error handling logic, specifically ensuring that xa_alloc_cyclic() return values are properly checked using negative value validation rather than relying solely on IS_ERR() macro behavior. The fix involves modifying the error checking code to explicitly verify that error codes are less than zero before proceeding with pointer dereference operations, which aligns with standard kernel development practices and security guidelines. System administrators should prioritize patching affected systems, particularly those running embedded Linux distributions or real-time operating systems where the dpll subsystem is heavily utilized. The fix demonstrates proper adherence to CWE principles regarding error handling and resource management, specifically addressing CWE-755 which deals with improper handling of exceptional conditions. Organizations should also implement monitoring for unusual system behavior that might indicate memory corruption or pointer-related issues, as the vulnerability could potentially be exploited to gain unauthorized access to kernel memory spaces. This vulnerability highlights the importance of rigorous testing for edge cases in kernel code, particularly in memory management functions where error propagation can have cascading effects throughout the system architecture.