CVE-2011-2183 in Linux
Summary
by MITRE
Race condition in the scan_get_next_rmap_item function in mm/ksm.c in the Linux kernel before 2.6.39.3, when Kernel SamePage Merging (KSM) is enabled, allows local users to cause a denial of service (NULL pointer dereference) or possibly have unspecified other impact via a crafted application.
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Analysis
by VulDB Data Team • 08/18/2024
The vulnerability identified as CVE-2011-2183 represents a critical race condition flaw within the Linux kernel's Kernel SamePage Merging implementation. This issue specifically affects the scan_get_next_rmap_item function located in the mm/ksm.c file, which is responsible for managing memory pages that are eligible for merging under KSM. The vulnerability manifests when KSM is enabled on systems running Linux kernel versions prior to 2.6.39.3, creating a window where concurrent operations can lead to unpredictable system behavior. The race condition occurs during the process of scanning memory regions and retrieving the next memory mapping item, which forms a fundamental part of how KSM identifies and merges identical memory pages across different processes.
The technical exploitation of this vulnerability relies on the improper handling of memory mapping references during concurrent access scenarios. When multiple threads or processes attempt to access the same memory mapping structure simultaneously while KSM is active, the function fails to properly synchronize access to shared data structures. This synchronization failure results in a situation where a pointer that should reference a valid memory mapping object becomes NULL, leading to a NULL pointer dereference when the system attempts to access the uninitialized reference. The flaw stems from inadequate locking mechanisms and improper state management within the KSM subsystem, which is designed to reduce memory consumption by merging identical pages across different virtual memory areas. This vulnerability operates at the kernel level and can be triggered through user-space applications that manipulate memory mappings in specific patterns, making it particularly dangerous as it can be exploited by local users without requiring elevated privileges.
The operational impact of CVE-2011-2183 extends beyond simple denial of service conditions to potentially encompass more severe consequences including system instability and arbitrary code execution. A successful exploitation can cause immediate system crashes through NULL pointer dereferences, resulting in kernel oops messages and system reboots that effectively deny service to legitimate users and applications. In some scenarios, the race condition may allow for more subtle memory corruption that could potentially be leveraged to escalate privileges or achieve arbitrary code execution within kernel space. The vulnerability affects systems where KSM is enabled, which is common in virtualized environments, containerized applications, and memory-intensive server configurations. Organizations running affected kernel versions face significant operational risks, particularly in cloud computing environments where KSM is frequently enabled to optimize memory usage across multiple virtual machines sharing identical memory pages. The impact is particularly severe in high-availability systems where unexpected kernel crashes can lead to service disruptions and data loss.
Mitigation strategies for CVE-2011-2183 primarily focus on kernel version updates and system configuration adjustments. The most effective remediation involves upgrading to Linux kernel version 2.6.39.3 or later, where the race condition has been properly addressed through improved synchronization mechanisms and enhanced locking protocols. System administrators should also consider disabling KSM on affected systems if the memory optimization benefits do not outweigh the security risks, particularly in environments where the vulnerability exposure is high. The implementation of proper kernel hardening measures including stack canaries, kernel address space layout randomization, and strict memory access controls can provide additional protection layers. Security monitoring should include detection of unusual kernel oops messages and system crash patterns that may indicate exploitation attempts. Organizations should also implement regular security assessments to identify systems running vulnerable kernel versions and establish patch management procedures that ensure timely deployment of security updates. This vulnerability aligns with CWE-362, which describes concurrent execution using shared resource with improper synchronization, and may map to ATT&CK techniques involving privilege escalation and denial of service through kernel exploits. The vulnerability demonstrates the critical importance of proper synchronization in kernel-level code and highlights the potential for seemingly minor race conditions to result in significant security impacts.