CVE-2005-0937 in Linux
Summary
by MITRE
some futex functions in futex.c for linux kernel 2.6.x perform get_user calls while holding the mmap_sem semaphore which could allow local users to cause a deadlock condition in do_page_fault by triggering get_user faults while another thread is executing mmap or other functions.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/02/2019
The vulnerability described in CVE-2005-0937 represents a critical concurrency issue within the Linux kernel's futex implementation that can lead to system deadlock conditions. This flaw exists in the futex.c file of Linux kernel versions 2.6.x and specifically affects the interaction between user space memory access operations and kernel synchronization primitives. The core problem manifests when certain futex functions execute get_user calls while maintaining hold of the mmap_sem semaphore, creating a dangerous scenario where system resources become permanently unavailable.
The technical flaw stems from improper lock ordering and resource management within the kernel's memory management subsystem. When a thread executing futex functions holds the mmap_sem semaphore and subsequently performs get_user operations to access user space memory, it creates a potential deadlock scenario. If another thread attempts to acquire the mmap_sem semaphore while the first thread is in the midst of a get_user fault handling operation, both threads can become blocked indefinitely. This condition violates fundamental principles of lock management and can result in complete system unresponsiveness. The issue is particularly insidious because it occurs during page fault handling operations, which are fundamental to memory management in the kernel.
The operational impact of this vulnerability extends beyond simple system hangs, as it can be exploited by local users to create denial of service conditions that may persist until system reboot. Attackers can craft specific sequences of operations that trigger the deadlock condition, effectively rendering the system unresponsive to legitimate user requests. The vulnerability affects the kernel's ability to handle memory management operations properly, particularly when multiple threads are simultaneously accessing memory mappings and futex operations. This creates a scenario where legitimate system functions become blocked, potentially affecting critical services and applications running on the system.
The vulnerability aligns with CWE-362, which describes concurrent execution using shared data structures without proper synchronization mechanisms. Additionally, this issue relates to ATT&CK technique T1499.004, which covers network denial of service through resource exhaustion. The flaw demonstrates poor adherence to kernel security principles where proper lock ordering and resource management practices are violated. Mitigation strategies should focus on ensuring that get_user operations are performed outside of critical kernel locks, particularly those protecting memory management structures. Kernel updates and patches addressing this specific race condition are essential, as are proper lock ordering practices that prevent the acquisition of multiple locks in inconsistent orders. System administrators should also implement monitoring for unusual memory management patterns that might indicate the onset of such deadlock conditions, and consider implementing additional safeguards to prevent local privilege escalation through resource exhaustion attacks.