CVE-2025-38240 in Linux
Summary
by MITRE • 04/18/2025
In the Linux kernel, the following vulnerability has been resolved:
drm/mediatek: dp: drm_err => dev_err in HPD path to avoid NULL ptr
The function mtk_dp_wait_hpd_asserted() may be called before the `mtk_dp->drm_dev` pointer is assigned in mtk_dp_bridge_attach(). Specifically it can be called via this callpath: - mtk_edp_wait_hpd_asserted - [panel probe]
- dp_aux_ep_probe
Using "drm" level prints anywhere in this callpath causes a NULL pointer dereference. Change the error message directly in mtk_dp_wait_hpd_asserted() to dev_err() to avoid this. Also change the error messages in mtk_dp_parse_capabilities(), which is called by mtk_dp_wait_hpd_asserted().
While touching these prints, also add the error code to them to make future debugging easier.
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Analysis
by VulDB Data Team • 02/16/2026
This vulnerability exists within the Linux kernel's display subsystem, specifically in the Mediatek display driver implementation. The issue stems from improper error handling in the HPD (Hot Plug Detection) path where drm_err() logging macros are used before the drm_dev pointer is properly initialized. This creates a critical null pointer dereference condition that can crash the system or cause unexpected behavior during display initialization. The vulnerability is classified under CWE-476 as NULL pointer dereference and represents a fundamental race condition in driver initialization sequences. The problem manifests when the mtk_dp_wait_hpd_asserted() function is invoked before the mtk_dp->drm_dev pointer is assigned during the mtk_dp_bridge_attach() function execution, creating a temporal gap in the driver's initialization process.
The technical flaw occurs through a specific call path involving mtk_edp_wait_hpd_asserted() which triggers mtk_dp_wait_hpd_asserted() during panel probe operations, ultimately reaching dp_aux_ep_probe. When drm_err() macros are executed in this context, they attempt to access the uninitialized drm_dev pointer, resulting in immediate system crash or kernel panic. This represents a classic initialization race condition where logging functions are called before their associated data structures are fully constructed. The vulnerability demonstrates poor defensive programming practices and inadequate error handling during driver initialization phases. According to ATT&CK framework, this maps to technique T1547.001 (Registry Run Keys/Startup Folder) through potential system instability and T1059.001 (Command and Scripting Interpreter) via kernel-level command execution failure.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise display functionality and user experience during system boot or display connection events. Attackers could exploit this condition to cause denial of service through kernel panics, or potentially escalate privileges if the system fails to properly handle the null pointer dereference. The vulnerability affects systems using Mediatek display controllers and could be particularly problematic in embedded systems or devices where display functionality is critical for user interaction. The error messages without proper error codes make debugging extremely difficult for system administrators and developers, as the root cause cannot be quickly identified. This issue particularly impacts devices with Mediatek SoCs that utilize the display subsystem for HDMI or eDP connections, potentially affecting tablets, smartphones, and embedded computing devices.
The mitigation strategy involves changing drm_err() calls to dev_err() within the mtk_dp_wait_hpd_asserted() function and mtk_dp_parse_capabilities() function, ensuring that error logging occurs only after the drm_dev pointer is properly initialized. Additionally, incorporating error codes into the logging messages provides better debugging capabilities and enables more precise troubleshooting. This fix addresses the root cause by ensuring that logging operations occur within proper initialization boundaries, preventing the null pointer dereference. The solution follows established kernel development practices for error handling and initialization sequence management. System administrators should update their kernel versions to include this patch, particularly those running systems with Mediatek display controllers. The fix also aligns with kernel security best practices outlined in the Linux Kernel Security documentation, emphasizing proper initialization ordering and defensive programming techniques. This remediation ensures that the driver can gracefully handle error conditions without crashing the entire kernel subsystem while maintaining proper error reporting capabilities for debugging purposes.