CVE-2016-7042 in Android
Summary
by MITRE
The proc_keys_show function in security/keys/proc.c in the Linux kernel through 4.8.2, when the GNU Compiler Collection (gcc) stack protector is enabled, uses an incorrect buffer size for certain timeout data, which allows local users to cause a denial of service (stack memory corruption and panic) by reading the /proc/keys file.
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Analysis
by VulDB Data Team • 10/27/2022
The vulnerability identified as CVE-2016-7042 represents a critical stack-based buffer overflow in the Linux kernel's key management subsystem. This flaw exists within the proc_keys_show function located in security/keys/proc.c, affecting Linux kernel versions through 4.8.2. The vulnerability manifests specifically when the GNU Compiler Collection's stack protector mechanism is enabled, creating a dangerous condition where memory corruption can occur during file system operations. The issue stems from an incorrect buffer size calculation that fails to properly account for timeout data when populating the /proc/keys virtual file system entry. This particular vulnerability demonstrates how compiler security features can interact unexpectedly with kernel code, creating conditions where seemingly benign operations can escalate into system-wide failures.
The technical exploitation of this vulnerability occurs through a carefully crafted sequence of operations that triggers the problematic code path in the kernel's key management system. When local users access the /proc/keys file, the kernel's internal function attempts to format and display key timeout information, but due to the miscalculated buffer size, it writes beyond the allocated memory boundaries. This stack corruption directly leads to kernel panic conditions, effectively causing a denial of service attack against the targeted system. The vulnerability's impact is particularly severe because it requires no special privileges beyond normal user access, making it exploitable by any local user with read permissions on the /proc filesystem. This represents a classic case of insufficient bounds checking in kernel space code, where the buffer overflow occurs during the generation of a virtual file system entry rather than during direct memory manipulation.
From an operational standpoint, this vulnerability creates a significant risk for systems that rely on the Linux kernel's key management infrastructure, particularly those running kernel versions up to 4.8.2. The denial of service condition it produces can render systems unusable, requiring manual intervention and system reboot to restore normal operation. The vulnerability's exploitation is relatively straightforward, requiring only the ability to read the /proc/keys file, which is typically accessible to all users on standard Linux installations. This characteristic makes the vulnerability particularly dangerous in multi-user environments where any local user could potentially trigger the condition and cause system-wide disruption. The vulnerability also highlights the importance of proper memory management in kernel code and demonstrates how seemingly minor implementation errors can have catastrophic consequences for system stability.
The mitigation strategies for CVE-2016-7042 primarily involve updating to patched kernel versions where the buffer size calculation has been corrected to properly account for timeout data. System administrators should prioritize kernel updates to versions that contain the appropriate fixes, which typically involve correcting the buffer allocation logic in the proc_keys_show function. Additionally, monitoring for unauthorized access to the /proc/keys file can serve as an early detection mechanism, though this approach only identifies exploitation attempts rather than preventing them. The vulnerability also underscores the importance of comprehensive testing of kernel code, particularly when compiler security features like stack protector are enabled. From a cybersecurity perspective, this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a typical example of how kernel-level buffer overflows can lead to privilege escalation and system compromise. Organizations should implement regular kernel patching procedures and maintain awareness of such vulnerabilities to prevent potential exploitation attempts that could disrupt critical system operations and compromise overall security posture.