Linux Kernel Null Pointer Dereference Vulnerability in AMD Display HDCP Module

A null pointer dereference vulnerability has been identified in the Linux kernel's AMD display module, specifically within the HDCP (High-bandwidth Digital Content Protection) handling code. The issue arises in the function 'mod_hdcp_hdcp1_create_session()', which calls 'get_first_active_display()' without verifying its return value. If the display list is empty, this function returns a null pointer, leading to a null pointer dereference. The vulnerability has been addressed by adding a null pointer check for 'get_first_active_display()' and returning 'MOD_HDCP_STATUS_DISPLAY_NOT_FOUND' if the function returns null. This issue affects several versions of the Linux kernel.

Impact

Exploitation of this vulnerability leads to a null pointer dereference, causing a crash or undefined behavior in the kernel.

Reproduction

To reproduce this vulnerability, invoke the 'mod_hdcp_hdcp1_create_session()' function when there are no active displays. The function will attempt to access the display list, and if it is empty, a null pointer dereference will occur, crashing the system.

Remediation

Users can upgrade to the latest version of the Linux kernel where this vulnerability has been fixed. Instructions for upgrading the kernel can be found in the official Linux kernel documentation.