CVE-2007-6716 in Linux
Summary
by MITRE
fs/direct-io.c in the dio subsystem in the Linux kernel before 2.6.23 does not properly zero out the dio struct, which allows local users to cause a denial of service (OOPS), as demonstrated by a certain fio test.
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Analysis
by VulDB Data Team • 08/02/2021
The vulnerability described in CVE-2007-6716 resides within the Linux kernel's direct I/O subsystem, specifically in the fs/direct-io.c file. This flaw affects kernel versions prior to 2.6.23 and represents a classic case of improper memory initialization that can lead to system instability. The issue manifests when the dio (direct I/O) structure fails to properly zero out its internal fields during initialization, creating a scenario where uninitialized memory contents can influence system behavior. The vulnerability was demonstrated through a specific fio test case that exploits this memory initialization flaw to trigger a kernel oops condition, effectively causing a system crash or denial of service.
The technical root cause of this vulnerability aligns with CWE-457, which addresses the use of uninitialized variables in programming contexts. In kernel space, this translates to improper initialization of data structures that are expected to be in a known state before use. When the dio structure is not properly zeroed, certain fields may contain residual data from previous operations or memory allocation patterns. This uninitialized data can then be interpreted by the kernel's I/O handling code in unexpected ways, leading to unpredictable behavior and ultimately system instability. The direct I/O subsystem is particularly sensitive to such initialization issues because it handles low-level block device operations where precise data structure contents are critical for correct operation.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise system reliability and availability. Local users with access to the system can exploit this weakness to force kernel panics or oops conditions, effectively rendering the system unstable and requiring manual intervention for recovery. This type of vulnerability is particularly concerning in production environments where system uptime and reliability are paramount. The attack vector is relatively simple since it only requires local user access, making it accessible to any user with login privileges on the affected system. From an attacker perspective, this vulnerability fits within the ATT&CK framework under the technique of privilege escalation and denial of service, though the specific implementation requires local access to execute.
Mitigation strategies for this vulnerability involve upgrading to Linux kernel version 2.6.23 or later, where the memory initialization issue has been corrected. System administrators should prioritize patching affected systems, particularly those running older kernel versions that may be exposed to local users. Additionally, implementing proper kernel security hardening measures such as disabling unnecessary I/O operations and monitoring for unusual kernel oops patterns can help detect exploitation attempts. The fix implemented in kernel 2.6.23 specifically addresses the memory zeroing issue in the dio structure initialization, ensuring that all fields are properly initialized to known values before use. Organizations should also consider implementing monitoring solutions that can detect kernel oops conditions and automatically alert security teams to potential exploitation attempts, as these events often precede system instability and service disruption.