CVE-2005-3807 in Linux
Summary
by MITRE
Memory leak in the VFS file lease handling in locks.c in Linux kernels 2.6.10 to 2.6.15 allows local users to cause a denial of service (memory exhaustion) via certain Samba activities that cause an fasync entry to be re-allocated by the fcntl_setlease function after the fasync queue has already been cleaned by the locks_delete_lock function.
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Analysis
by VulDB Data Team • 12/18/2024
The vulnerability described in CVE-2005-3807 represents a critical memory management flaw within the Linux kernel's Virtual File System layer, specifically affecting kernel versions between 2.6.10 and 2.6.15. This issue manifests as a memory leak that occurs during the handling of file leases, which are mechanisms used to coordinate access to files between different processes. The vulnerability is particularly significant because it can be exploited by local users to cause a denial of service condition through memory exhaustion, effectively rendering the system unstable or unresponsive.
The technical root cause of this vulnerability lies in the improper synchronization between two kernel functions within the locks.c file: fcntl_setlease and locks_delete_lock. When Samba activities trigger specific file locking operations, the kernel's lease handling mechanism attempts to re-allocate an fasync entry through the fcntl_setlease function. However, this re-allocation occurs after the fasync queue has already been cleaned by the locks_delete_lock function, creating a scenario where memory allocated for the fasync entry is not properly released. This results in a gradual accumulation of unreleased memory blocks that eventually leads to system memory exhaustion.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can be exploited by malicious local users to systematically consume available system memory without requiring elevated privileges. The memory leak occurs in a way that is particularly insidious because it does not immediately crash the system but rather gradually depletes available memory resources, making it difficult to detect and diagnose. The vulnerability is specifically triggered by certain Samba activities, which means that systems running Samba servers or clients are particularly at risk, though any local user with access to the system could potentially exploit this weakness to cause service disruption.
This memory leak vulnerability can be classified under CWE-401 as a failure to release memory resources, and it aligns with ATT&CK technique T1499.001 for resource exhaustion attacks. The flaw demonstrates poor memory management practices in kernel space, where the cleanup functions do not properly account for all allocated resources, particularly in scenarios involving asynchronous notification mechanisms. The vulnerability represents a classic case of improper resource management that can be exploited to create persistent denial of service conditions. Organizations should prioritize applying kernel updates to address this vulnerability, as the memory exhaustion can lead to system instability and potential service interruptions that may affect critical operations.
The exploitation of this vulnerability highlights the importance of proper synchronization between kernel subsystems and the need for comprehensive memory management practices in operating system code. The fact that this issue was present in multiple kernel versions indicates a systemic problem in the implementation of file lease handling that required immediate attention. System administrators should monitor for signs of memory exhaustion and implement appropriate resource limits to mitigate the impact of such vulnerabilities while awaiting security patches. The vulnerability serves as a reminder of the critical importance of thorough testing and validation of kernel code, particularly in areas involving resource allocation and deallocation mechanisms that are fundamental to system stability and security.