CVE-2024-26729 in Linux
Summary
by MITRE • 04/03/2024
In the Linux kernel, the following vulnerability has been resolved:
drm/amd/display: Fix potential null pointer dereference in dc_dmub_srv
Fixes potential null pointer dereference warnings in the dc_dmub_srv_cmd_list_queue_execute() and dc_dmub_srv_is_hw_pwr_up() functions.
In both functions, the 'dc_dmub_srv' variable was being dereferenced before it was checked for null. This could lead to a null pointer dereference if 'dc_dmub_srv' is null. The fix is to check if 'dc_dmub_srv' is null before dereferencing it.
Thus moving the null checks for 'dc_dmub_srv' to the beginning of the functions to ensure that 'dc_dmub_srv' is not null when it is dereferenced.
Found by smatch & thus fixing the below: drivers/gpu/drm/amd/amdgpu/../display/dc/dc_dmub_srv.c:133 dc_dmub_srv_cmd_list_queue_execute() warn: variable dereferenced before check 'dc_dmub_srv' (see line 128) drivers/gpu/drm/amd/amdgpu/../display/dc/dc_dmub_srv.c:1167 dc_dmub_srv_is_hw_pwr_up() warn: variable dereferenced before check 'dc_dmub_srv' (see line 1164)
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Analysis
by VulDB Data Team • 08/03/2025
The vulnerability identified as CVE-2024-26729 represents a critical null pointer dereference flaw within the AMD display subsystem of the Linux kernel's Direct Rendering Manager framework. This issue specifically affects the drm/amd/display component where the dc_dmub_srv structure is manipulated during hardware power management operations. The vulnerability stems from improper null pointer validation in two core functions that handle display controller communication with the Display Microcontroller Unit Bridge, creating potential system instability and denial of service conditions when display hardware is accessed without proper initialization checks.
The technical flaw manifests in two distinct functions where the dc_dmub_srv structure pointer is dereferenced before null validation occurs. In dc_dmub_srv_cmd_list_queue_execute() function, the pointer is accessed at line 133 while the null check occurs at line 128, and similarly in dc_dmub_srv_is_hw_pwr_up() where the dereference happens at line 1167 before the validation at line 1164. This pattern violates fundamental defensive programming principles and creates a window where malicious actors or system errors could trigger immediate system crashes or unpredictable behavior. The flaw directly maps to CWE-476 which describes null pointer dereference conditions, and represents a classic example of improper null pointer validation in kernel space code where the consequences extend beyond simple application crashes to potential system-wide instability.
The operational impact of this vulnerability extends beyond simple system crashes as it affects the core display subsystem functionality that users depend on for graphics rendering and hardware management. When these functions are invoked during display initialization, power state transitions, or hardware status checks, a null pointer dereference can result in immediate kernel panics, system lockups, or forced reboots that disrupt user experience and potentially compromise system availability. The vulnerability is particularly concerning in embedded systems or server environments where continuous display functionality is critical, and where such failures could lead to complete system unavailability. The issue affects systems utilizing AMD graphics hardware where the display microcontroller unit bridge communication is actively used, making it relevant to a broad range of computing platforms from desktops to servers.
The fix implemented addresses the root cause by repositioning null pointer checks to occur before any dereference operations within both affected functions. This defensive programming approach ensures that the dc_dmub_srv structure pointer is validated before any access attempts, preventing the null pointer dereference conditions that previously existed. The solution follows established security practices for kernel development and aligns with ATT&CK technique T1499.004 which covers system network denial of service through kernel-level vulnerabilities. System administrators should prioritize applying this patch across all affected Linux distributions, particularly in environments where AMD graphics hardware is actively utilized and where system stability is paramount. The remediation process should include thorough testing of display functionality post-patch to ensure no regressions in graphics performance or hardware compatibility occur during normal operation.