CVE-2016-9754 in Linux
Summary
by MITRE • 01/25/2023
The ring_buffer_resize function in kernel/trace/ring_buffer.c in the profiling subsystem in the Linux kernel before 4.6.1 mishandles certain integer calculations, which allows local users to gain privileges by writing to the /sys/kernel/debug/tracing/buffer_size_kb file.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability described in CVE-2016-9754 resides within the Linux kernel's profiling subsystem, specifically in the ring_buffer_resize function located in kernel/trace/ring_buffer.c. This flaw represents a classic integer overflow or underflow issue that occurs during buffer size calculations when modifying the /sys/kernel/debug/tracing/buffer_size_kb file. The vulnerability affects Linux kernel versions prior to 4.6.1 and provides local attackers with a path to privilege escalation through improper handling of integer arithmetic operations.
The technical implementation of this vulnerability stems from the ring_buffer_resize function's failure to properly validate or handle integer calculations when resizing trace buffers. When a local user writes to the /sys/kernel/debug/tracing/buffer_size_kb file, the kernel performs calculations to determine the new buffer size. Due to inadequate integer overflow checks, these calculations can produce unexpected results that allow the attacker to manipulate memory layout or access kernel structures. This particular flaw falls under CWE-191, which specifically addresses integer underflow and overflow conditions, and more broadly aligns with CWE-190, covering integer overflow and underflow vulnerabilities. The attack vector is particularly concerning because it requires only local user access and leverages the kernel's debug interface which is often accessible to unprivileged users in many system configurations.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it allows attackers to potentially gain root privileges and execute arbitrary code with kernel-level permissions. This creates a significant threat surface since the /sys/kernel/debug/tracing interface is typically available to local users for debugging purposes, making the attack surface more accessible than many other kernel vulnerabilities. The vulnerability can be exploited to bypass security controls, read sensitive kernel memory, modify kernel data structures, or even implement persistent backdoors. From an ATT&CK perspective, this vulnerability maps to T1068, which covers privilege escalation through local exploits, and T1543, covering persistence mechanisms that could be established through kernel-level modifications.
Mitigation strategies for CVE-2016-9754 involve upgrading to Linux kernel version 4.6.1 or later, where the integer calculation handling has been properly addressed. System administrators should also implement strict access controls on the /sys/kernel/debug/tracing directory and its files to limit local user access to these kernel debugging interfaces. Additional defensive measures include monitoring for unusual writes to the buffer_size_kb file, implementing kernel hardening techniques such as stack canaries, and employing kernel module signing to prevent unauthorized kernel modifications. Organizations should conduct regular security audits of their kernel configurations and ensure that debug interfaces are disabled or restricted in production environments where unnecessary. The fix implemented in kernel 4.6.1 involved proper integer overflow checks and validation of buffer size calculations to prevent the malicious manipulation of kernel memory structures through crafted input values.