CVE-2016-5828 in Linux
Summary
by MITRE • 01/25/2023
The start_thread function in arch/powerpc/kernel/process.c in the Linux kernel through 4.6.3 on powerpc platforms mishandles transactional state, which allows local users to cause a denial of service (invalid process state or TM Bad Thing exception, and system crash) or possibly have unspecified other impact by starting and suspending a transaction before an exec system call.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability described in CVE-2016-5828 represents a critical flaw in the Linux kernel's transactional memory implementation on powerpc architectures. This issue resides within the start_thread function located in arch/powerpc/kernel/process.c, affecting kernel versions through 4.6.3. The flaw specifically targets the handling of transactional state during thread initialization, creating a scenario where local attackers can manipulate the kernel's transactional memory subsystem in ways that were not properly accounted for in the original design. The vulnerability stems from improper state management when transitioning between different transactional execution modes, particularly when dealing with suspended transactions that occur before an exec system call is invoked.
The technical implementation of this vulnerability exploits the fundamental transactional memory mechanisms that were introduced to improve performance on powerpc platforms. When a thread is initialized through the start_thread function, the kernel must properly manage the transactional state of the process. However, the flaw allows for a race condition or state corruption scenario where a transaction is started and suspended before an exec system call executes. This creates an inconsistent state within the kernel's transactional memory management subsystem, leading to either invalid process states or triggering TM Bad Thing exceptions. The transactional memory subsystem in powerpc processors provides hardware support for executing code transactionally, allowing operations to be rolled back if certain conditions are met, but this vulnerability demonstrates how improper state handling can lead to system instability.
From an operational perspective, this vulnerability presents significant risks to system stability and availability. Local users who can execute code on the affected system can trigger either a denial of service condition that crashes the entire system or potentially cause more subtle and unpredictable behavior that could lead to data corruption or privilege escalation. The impact extends beyond simple system crashes since the vulnerability could be exploited to create conditions where the kernel enters an inconsistent state that might be difficult to recover from automatically. The nature of transactional memory makes this particularly dangerous because the hardware-level transactional execution can be left in an undefined state, potentially causing cascading failures throughout the system's memory management and process scheduling components.
The vulnerability aligns with several cybersecurity frameworks and threat modeling approaches, particularly those addressing kernel-level exploits and privilege escalation vectors. From a CWE perspective, this represents a weakness in transactional memory state management and improper handling of system calls during process transitions. The ATT&CK framework would categorize this under privilege escalation and defense evasion techniques, as local users can leverage this flaw to either crash systems or potentially gain more persistent access. The vulnerability also relates to the broader category of race condition exploits, where timing issues in kernel code execution create opportunities for state corruption. Mitigation strategies should focus on kernel updates and patches that properly handle transactional state transitions, along with monitoring for unusual transactional memory behavior that might indicate exploitation attempts.
The remediation approach for CVE-2016-5828 requires immediate kernel patching to address the transactional state handling in the start_thread function. System administrators should prioritize updating to kernel versions that contain the specific fixes for this vulnerability, as the flaw exists at the core of process management on powerpc platforms. Additionally, organizations should implement monitoring solutions that can detect unusual transactional memory behavior or frequent exec system call patterns that might indicate exploitation attempts. The fix typically involves ensuring proper state cleanup and validation when transitioning between transactional and non-transactional execution modes, particularly during thread initialization and process execution transitions. Given the hardware-level nature of transactional memory on powerpc systems, organizations should also consider reviewing their security configurations and implementing additional process isolation measures to limit the potential impact of any remaining vulnerabilities in the transactional memory subsystem.