CVE-2004-2660 in Linux
Summary
by MITRE
Memory leak in direct-io.c in Linux kernel 2.6.x before 2.6.10 allows local users to cause a denial of service (memory consumption) via certain O_DIRECT (direct IO) write requests.
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Analysis
by VulDB Data Team • 06/24/2019
The vulnerability described in CVE-2004-2660 represents a critical memory management flaw within the Linux kernel's direct I/O implementation that affects versions 2.6.x prior to 2.6.10. This memory leak occurs specifically within the direct-io.c component of the kernel's storage subsystem, where improper handling of certain O_DIRECT write operations leads to gradual memory consumption without proper cleanup. The flaw manifests when local users execute specific direct I/O write requests that trigger the kernel to allocate memory pages but fail to release them back to the system. This vulnerability falls under the CWE-401 category of CWE-401: Improper Release of Memory After Effective Use, which is a well-documented weakness in memory management practices that directly impacts system stability and resource availability. The issue is particularly concerning because it operates at the kernel level, meaning that any process running on the system can potentially exploit this weakness to consume available memory resources.
The technical implementation of this vulnerability exploits the kernel's direct I/O handling mechanism where the O_DIRECT flag bypasses the kernel's page cache and writes data directly to storage devices. When certain combinations of write parameters and file system conditions are met, the kernel's direct I/O code path fails to properly clean up allocated memory structures, particularly those related to asynchronous I/O operations and buffer management. The memory leak accumulates over time as users repeatedly execute direct I/O write operations, with each failed cleanup operation consuming additional memory that cannot be reclaimed by the system. This behavior creates a gradual degradation of system performance that eventually leads to memory exhaustion, making the system unresponsive or causing other processes to fail due to insufficient available memory. The vulnerability demonstrates a classic case of resource leak in kernel space, where the lack of proper error handling and cleanup routines during I/O processing creates a persistent drain on system resources.
The operational impact of CVE-2004-2660 extends beyond simple resource exhaustion to potentially compromise entire system availability and stability. Local users can exploit this vulnerability to systematically consume memory resources, effectively creating a denial of service condition that affects not just individual processes but the entire operating system. The memory consumption occurs gradually, making it difficult to detect initially, but the cumulative effect can render systems unusable over time. Systems running vulnerable kernel versions become increasingly susceptible to memory pressure, which can trigger system crashes, process termination, or severe performance degradation. This vulnerability aligns with ATT&CK technique T1499.001: Network Denial of Service, where the attack vector targets system resources rather than network connectivity, and represents a form of resource exhaustion attack that can be particularly devastating in server environments where memory resources are critical for normal operations. The vulnerability's exploitation is relatively simple and requires no special privileges beyond standard user access, making it a significant concern for system administrators who must ensure their kernel versions are properly updated.
Mitigation strategies for CVE-2004-2660 focus primarily on kernel version updates and system hardening measures. The most effective solution involves upgrading to Linux kernel version 2.6.10 or later, where the memory leak in direct-io.c has been properly addressed through enhanced cleanup routines and improved error handling. System administrators should implement regular patch management procedures to ensure all kernel components remain current with security fixes. Additionally, monitoring system memory usage and implementing automated alerts for unusual memory consumption patterns can help detect exploitation attempts before they cause significant damage. The vulnerability highlights the importance of kernel security testing and the need for comprehensive memory management validation in operating system components. Organizations should also consider implementing resource limits and process monitoring to prevent individual processes from consuming excessive memory. The fix implemented in kernel 2.6.10 demonstrates the importance of proper resource management in kernel space, where every allocated memory block must have a corresponding deallocation mechanism to prevent long-term system degradation. This vulnerability serves as a reminder of the critical nature of kernel security and the potential for seemingly minor memory management flaws to have significant operational impacts on system availability and stability.