CVE-2008-4934 in Linux
Summary
by MITRE
The hfsplus_block_allocate function in fs/hfsplus/bitmap.c in the Linux kernel before 2.6.28-rc1 does not check a certain return value from the read_mapping_page function before calling kmap, which allows attackers to cause a denial of service (system crash) via a crafted hfsplus filesystem image.
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Analysis
by VulDB Data Team • 08/21/2019
The vulnerability described in CVE-2008-4934 represents a critical flaw in the Linux kernel's handling of HFS+ filesystems, specifically within the hfsplus_block_allocate function located in fs/hfsplus/bitmap.c. This issue affects Linux kernel versions prior to 2.6.28-rc1 and demonstrates a classic case of improper error handling that can lead to system instability. The flaw occurs when the kernel attempts to allocate blocks on an HFS+ filesystem, where the function fails to properly validate the return value from the read_mapping_page function before proceeding to call kmap. This oversight creates a scenario where an attacker can craft a malicious HFS+ filesystem image that triggers an improper memory mapping operation, ultimately resulting in a system crash or denial of service condition.
The technical root cause of this vulnerability aligns with CWE-252, which describes an issue where an error condition is not properly handled or checked, leading to unexpected behavior in software systems. The vulnerability operates at the kernel level where the hfsplus_block_allocate function expects a successful return from read_mapping_page to ensure proper memory page handling before calling kmap. When read_mapping_page fails to return the expected success status, the subsequent kmap call attempts to map a non-existent or invalid page, causing a kernel panic or system crash. This represents a fundamental flaw in the kernel's filesystem handling logic where error propagation is not properly implemented, allowing an attacker to exploit the missing validation check and induce system instability.
From an operational perspective, this vulnerability presents a significant risk to systems running Linux kernels vulnerable to CVE-2008-4934, particularly those that mount or process HFS+ filesystems. The attack vector requires an attacker to create or provide a specially crafted HFS+ filesystem image that will trigger the specific code path leading to the error condition. Once executed, the vulnerability results in immediate system crash or hang, effectively causing a denial of service that can impact availability of critical services or systems that rely on HFS+ filesystem support. The impact extends beyond simple system crashes as it can affect any system that processes HFS+ data, including servers, desktop systems, or embedded devices that may encounter such filesystems through various means such as external drives, network shares, or automated processing systems.
The mitigation strategies for this vulnerability involve immediate kernel updates to versions 2.6.28-rc1 or later where the proper error handling has been implemented. System administrators should prioritize patching affected systems and ensure that all kernel components are updated to versions that contain the fix for this specific vulnerability. Additionally, implementing proper filesystem validation and monitoring for suspicious HFS+ images can help detect potential exploitation attempts. The fix for this vulnerability typically involves adding proper error checking after the read_mapping_page call to ensure that the return value is validated before proceeding with the kmap operation, thereby preventing the kernel from attempting to map invalid memory pages. Organizations should also consider implementing access controls and filesystem isolation measures to limit exposure to potentially malicious HFS+ images, particularly in environments where untrusted filesystems may be mounted or processed. This vulnerability demonstrates the importance of proper error handling in kernel code and aligns with ATT&CK technique T1499.004 for Denial of Service through kernel-level exploitation.