CVE-2008-7316 in Linux
Summary
by MITRE
mm/filemap.c in the Linux kernel before 2.6.25 allows local users to cause a denial of service (infinite loop) via a writev system call that triggers an iovec of zero length, followed by a page fault for an iovec of nonzero length.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability described in CVE-2008-7316 represents a critical denial of service flaw within the Linux kernel's memory management subsystem, specifically in the filemap.c component that handles memory mapping operations. This issue affects Linux kernel versions prior to 2.6.25 and demonstrates how improper handling of input validation can lead to system instability. The vulnerability manifests when a local user executes a writev system call with a specific sequence of iovec structures that contain zero-length entries followed by nonzero-length entries, creating an exploitable condition that can bring the entire system to a halt.
The technical root cause of this vulnerability lies in the kernel's memory management code failing to properly validate the length parameters of iovec structures during writev operations. When the kernel processes a writev call containing a zero-length iovec entry, it enters a processing loop that does not correctly handle the transition to subsequent nonzero-length entries. This creates an infinite loop condition where the kernel continuously processes the same zero-length entry without proper termination logic, consuming system resources and effectively rendering the system unresponsive. The flaw operates at the kernel level within the mm/filemap.c file, which manages memory mapping operations between file systems and virtual memory, making it particularly dangerous as it can be triggered through standard system calls that any local user can execute.
The operational impact of this vulnerability extends beyond simple system unresponsiveness to potentially compromising system availability and stability. Local users can exploit this condition to perform denial of service attacks against running systems, causing legitimate processes to hang indefinitely while the kernel remains trapped in the infinite loop. This vulnerability is especially concerning in multi-user environments or systems where local access is not strictly controlled, as any user with access to execute writev system calls can potentially trigger the condition. The infinite loop consumes CPU resources and prevents the kernel from processing other legitimate requests, effectively creating a denial of service scenario that can persist until the system is manually rebooted or the kernel is patched.
Mitigation strategies for this vulnerability focus primarily on applying the appropriate kernel security patches that were released as part of the Linux kernel 2.6.25 release and subsequent versions. System administrators should immediately update their kernel versions to 2.6.25 or later to eliminate this vulnerability. Additionally, monitoring systems should be configured to detect unusual patterns of writev system calls that might indicate exploitation attempts. The vulnerability aligns with CWE-835, which describes the weakness of an infinite loop in software, and represents a classic example of how improper input validation can lead to system instability. From an ATT&CK perspective, this vulnerability maps to the technique of privilege escalation and denial of service, as local users can leverage it to compromise system availability. Organizations should also consider implementing access controls and limiting local user privileges where possible to reduce the attack surface, while maintaining regular kernel updates as part of their overall security posture to prevent similar vulnerabilities from being exploited in the future.