CVE-2018-20449 in Linux
Summary
by MITRE
The hidma_chan_stats function in drivers/dma/qcom/hidma_dbg.c in the Linux kernel 4.14.90 allows local users to obtain sensitive address information by reading "callback=" lines in a debugfs file.
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Analysis
by VulDB Data Team • 05/25/2020
The vulnerability identified as CVE-2018-20449 resides within the Linux kernel's Qualcomm HIMA DMA driver, specifically in the hidma_chan_stats function located in drivers/dma/qcom/hidma_dbg.c. This issue represents a classic information disclosure flaw that occurs when debug functionality is improperly configured for production use. The vulnerability affects Linux kernel versions up to and including 4.14.90, making it a significant concern for systems utilizing Qualcomm's high-performance DMA controllers. The flaw manifests when local users can access debugfs files through the callback= parameter, which inadvertently exposes kernel memory addresses to unauthorized local entities.
The technical implementation of this vulnerability stems from insufficient access controls and improper sanitization of debug output within the DMA driver's debugging interface. When the hidma_chan_stats function processes channel statistics, it includes callback function pointers in the debugfs output without proper obfuscation or access restriction mechanisms. This creates a scenario where any local user with access to the debugfs filesystem can read these callback= lines and extract kernel virtual addresses, which can be leveraged for further exploitation attempts. The vulnerability directly relates to CWE-200, Information Exposure, and more specifically CWE-427, Uncontrolled Search Path Element, as it involves the exposure of sensitive memory locations through debug interfaces that should be restricted.
The operational impact of this vulnerability extends beyond simple information disclosure, as the leaked kernel addresses can serve as critical information for advanced exploitation techniques. Attackers can use the exposed memory addresses to bypass kernel address space layout randomization defenses, which are fundamental security mechanisms designed to prevent exploitation of memory corruption vulnerabilities. This information disclosure can enable local privilege escalation attacks or facilitate more sophisticated exploitation chains where attackers need precise memory layout information to craft effective exploits. The vulnerability affects systems running Linux kernel versions 4.14.90 and earlier, particularly those utilizing Qualcomm's HIMA DMA hardware, making it relevant to mobile devices, embedded systems, and other platforms using this specific driver implementation.
Mitigation strategies for CVE-2018-20449 focus on both immediate patching and defensive configuration measures. The primary solution involves upgrading to a Linux kernel version that contains the fix for this vulnerability, typically kernel versions 4.15 and later where the debugfs output has been properly restricted. System administrators should also implement strict access controls on debugfs filesystems, ensuring that only authorized personnel can access these sensitive interfaces. Additionally, the vulnerability can be mitigated through kernel configuration options that disable debugfs functionality for production systems or through the use of security modules that enforce stricter access controls. From an ATT&CK framework perspective, this vulnerability aligns with T1059.001 Command and Scripting Interpreter: PowerShell and T1068.001 Exploitation for Privilege Escalation, as it provides the initial information gathering necessary for more sophisticated attacks. Organizations should also consider implementing kernel lockdown modes and other hardening measures that prevent local users from accessing sensitive kernel debugging interfaces.