CVE-2015-1420 in Linux
Summary
by MITRE
Race condition in the handle_to_path function in fs/fhandle.c in the Linux kernel through 3.19.1 allows local users to bypass intended size restrictions and trigger read operations on additional memory locations by changing the handle_bytes value of a file handle during the execution of this function.
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Analysis
by VulDB Data Team • 03/08/2022
The vulnerability identified as CVE-2015-1420 represents a critical race condition flaw within the Linux kernel's file handle management subsystem. This issue resides in the handle_to_path function located in fs/fhandle.c, affecting kernel versions through 3.19.1. The race condition occurs when a malicious local user manipulates the handle_bytes value of a file handle while the handle_to_path function is actively processing, creating a temporal window where the kernel's memory access controls can be circumvented. The flaw fundamentally exploits the lack of proper synchronization mechanisms during file handle conversion operations, allowing attackers to manipulate memory access patterns that should otherwise be restricted by size limitations inherent to the file handle structure.
The technical implementation of this vulnerability stems from the kernel's failure to properly validate or lock the file handle metadata during the conversion process from file handle to path representation. When the handle_to_path function executes, it relies on the handle_bytes parameter to determine the boundaries of memory operations and validate the integrity of file handle data. However, the race condition allows a local attacker to modify this parameter between the time the function begins execution and when it completes its memory operations, effectively bypassing the intended size restrictions that would normally prevent access to adjacent memory locations. This manipulation creates a scenario where the kernel's memory management routines can be tricked into performing read operations on memory regions that should remain protected, potentially exposing sensitive kernel data or allowing for privilege escalation.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides a pathway for local users to potentially access memory locations that contain critical kernel data structures, credentials, or other sensitive information. The race condition nature of the flaw means that exploitation requires precise timing and specific conditions, but once successful, it can enable attackers to gather kernel memory contents, potentially leading to further exploitation vectors such as kernel address space layout randomization (ASLR) bypass or privilege escalation. From an attacker perspective, this vulnerability aligns with the MITRE ATT&CK framework's technique T1068, which involves local privilege escalation through kernel exploits, and represents a significant weakening of the kernel's memory protection mechanisms that are fundamental to system security.
The vulnerability demonstrates a clear violation of the CWE-362 principle of concurrent execution with improper synchronization, where the lack of proper locking mechanisms during critical operations creates exploitable race conditions. The flaw also relates to CWE-129, which addresses improper validation of array indices, as the handle_bytes parameter essentially controls array bounds during memory operations. System administrators and security professionals should recognize this vulnerability as requiring immediate kernel updates and patch management, as it represents a fundamental weakness in the kernel's file handle handling that could be leveraged for more sophisticated attacks. The remediation approach must focus on implementing proper synchronization mechanisms around the handle_to_path function and ensuring that file handle metadata cannot be modified during active processing operations. Organizations should also consider monitoring for potential exploitation attempts through unusual file handle manipulation patterns and implement kernel hardening measures to limit the attack surface of such vulnerabilities.