CVE-2008-3535 in Linux
Summary
by MITRE
Off-by-one error in the iov_iter_advance function in mm/filemap.c in the Linux kernel before 2.6.27-rc2 allows local users to cause a denial of service (system crash) via a certain sequence of file I/O operations with readv and writev, as demonstrated by testcases/kernel/fs/ftest/ftest03 from the Linux Test Project.
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Analysis
by VulDB Data Team • 08/17/2019
The vulnerability described in CVE-2008-3535 represents a critical off-by-one error within the Linux kernel's memory management subsystem that specifically affects the iov_iter_advance function located in mm/filemap.c. This flaw exists in kernel versions prior to 2.6.27-rc2 and demonstrates how seemingly minor programming errors can lead to severe system instability. The issue manifests when specific sequences of file I/O operations are executed using the readv and writev system calls, which are designed to handle vectorized I/O operations where data is read from or written to multiple buffers simultaneously. The vulnerability is particularly concerning because it allows local attackers to trigger a system crash without requiring special privileges, making it a significant denial of service threat.
The technical root cause of this vulnerability lies in the improper handling of buffer boundaries within the iov_iter_advance function, which is responsible for advancing through input/output vectors during I/O operations. When readv and writev system calls are used in certain combinations, the function fails to properly validate the boundary conditions of the data buffers, leading to an off-by-one error that can cause memory corruption. This type of error falls under CWE-129, which specifically addresses Improper Validation of Array Index, and represents a classic example of how boundary condition errors can result in memory safety issues. The vulnerability is triggered when the kernel's I/O iterator logic incorrectly calculates buffer positions, potentially causing the system to access memory outside of allocated boundaries.
From an operational perspective, this vulnerability presents a substantial risk to Linux systems as it enables local users to cause system crashes through legitimate I/O operations. The attack vector requires only that an attacker execute specific combinations of readv and writev calls, which are common system operations that applications frequently use. This makes the vulnerability particularly dangerous because it can be exploited through normal system usage patterns rather than requiring specialized attack tools or conditions. The impact extends beyond simple system instability, as repeated exploitation can lead to system unavailability and potential data loss. According to ATT&CK framework, this vulnerability maps to T1499.004 which covers Network Denial of Service, and T1566.001 for Phishing with Social Engineering, as it can be leveraged in targeted attacks where local access is obtained to trigger system crashes.
The exploitation of CVE-2008-3535 demonstrates the importance of thorough input validation in kernel space operations and highlights the need for comprehensive testing of system call interfaces. The vulnerability was successfully demonstrated using testcases from the Linux Test Project, specifically the ftest03 test case, which shows how standard testing frameworks can identify critical security flaws in kernel code. Organizations should implement immediate patching strategies to address this vulnerability, as the Linux kernel version 2.6.27-rc2 and later versions contain the necessary fixes. Additionally, system administrators should monitor for any signs of exploitation attempts and consider implementing additional security controls such as kernel hardening measures and process monitoring to detect abnormal I/O patterns that might indicate attempted exploitation of this vulnerability.