CVE-2018-19939 in Mi A2 Lite
Summary
by MITRE
The Goodix GT9xx touchscreen driver for custom Linux kernels on Xiaomi daisy-o-oss Mi A2 Lite and RedMi6 pro devices through 2018-08-27 has a NULL pointer dereference in kfree after a kmalloc failure in gtp_read_Color in drivers/input/touchscreen/gt917d/gt9xx.c.
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Analysis
by VulDB Data Team • 06/13/2023
The vulnerability identified as CVE-2018-19939 represents a critical null pointer dereference flaw within the Goodix GT9xx touchscreen driver implementation for Linux kernels running on specific Xiaomi mobile devices. This issue affects the Mi A2 Lite and RedMi6 pro models through the specified date, indicating a widespread impact across multiple device generations within the Xiaomi ecosystem. The flaw manifests specifically within the kernel-space driver component responsible for touchscreen functionality, creating a potential pathway for system instability and denial of service conditions that could compromise device reliability and user experience.
The technical root cause of this vulnerability lies in improper error handling within the gtp_read_Color function located in drivers/input/touchscreen/gt917d/gt9xx.c. When the kmalloc memory allocation function fails to secure the required memory resources, the driver does not properly validate the allocation result before proceeding with subsequent operations. This failure to check for allocation success leads to a scenario where the kfree function is called on a NULL pointer, resulting in an immediate system crash or kernel panic. The vulnerability directly maps to CWE-476 which identifies null pointer dereference as a common programming error that can lead to system instability and potential exploitation.
The operational impact of this vulnerability extends beyond simple system crashes, as it can be leveraged to create persistent denial of service conditions that render the touchscreen functionality completely inoperable. This affects not only the user interface responsiveness but also potentially compromises the device's overall stability since touchscreen input is fundamental to device operation. The vulnerability is particularly concerning in mobile environments where kernel-level drivers directly control hardware interfaces, as any instability can lead to complete device lockups or forced reboots that disrupt user activities and potentially compromise device security.
From an attack perspective, this vulnerability aligns with ATT&CK technique T1068 which covers local privilege escalation and system compromise through kernel exploits. While the vulnerability itself may not directly enable remote code execution, it creates conditions that could be exploited as part of a broader attack chain. The flaw demonstrates poor defensive programming practices in kernel-space code where proper error handling and resource management protocols are not adequately implemented. This type of vulnerability is particularly dangerous because it operates at the kernel level where privilege escalation is not required to trigger the exploitation, making it a prime target for attackers seeking to establish persistent system control.
Mitigation strategies for this vulnerability primarily involve applying the manufacturer-provided kernel updates and firmware patches that address the specific memory allocation error handling within the touchscreen driver. System administrators and device manufacturers should prioritize immediate deployment of these patches to prevent exploitation. Additionally, implementing proper kernel memory management practices such as thorough validation of memory allocation results before subsequent operations can prevent similar issues in future driver implementations. The vulnerability underscores the importance of rigorous code review processes for kernel-space drivers and adherence to secure coding practices that prevent resource management errors from creating exploitable conditions in embedded mobile systems.