CVE-2026-98926 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amd/display: Remove sink usage from DPMS
[Why]
stream->sink is optional and can be null, so should always be checked before dereference. Additionally, most of its usage in DPMS sequences is for stream->sink->link, which can be replaced with stream->link, as the two should always be the same.
[How]
* Replace stream->sink->link in DPMS on/off * Add assert to USB4 BW allocation where sink is required * Avoid inconsistencies in resource access, e.g. don't repeat stream->link after it was already saved to a local variable * Pull out effective VPG calculation to helper getter * Formatting fixes
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel's Direct Rendering Manager subsystem for AMD display drivers contained a critical null pointer dereference vulnerability within the Display Power Management Sequencing logic. This flaw originated from an assumption that the stream sink structure was always present and valid during power state transitions. In reality, the stream->sink member is optional and can legitimately be NULL in various operational scenarios, particularly when handling specific display configurations or hardware states where a direct sink association does not exist. The code previously attempted to dereference this pointer without performing an initial null check, leading to potential kernel panics or system crashes if the condition was triggered during runtime operations such as screen on/off cycles.
The technical root cause lies in the improper handling of optional data structures within the Display Power Management Sequencing routines. When the driver executed DPMS commands, it accessed stream->sink->link without verifying that stream->sink was not null. This lack of defensive programming violates fundamental memory safety principles and creates a predictable crash vector for attackers or system instability under normal usage patterns where certain display pipelines are inactive or disconnected. The vulnerability is classified as CWE-476, which denotes NULL Pointer Dereference, indicating a failure to validate pointers before use, resulting in unauthorized access violations that compromise the availability of the operating system.
To resolve this issue, developers implemented several structural improvements within the AMD display driver codebase. First, all instances where stream->sink->link was accessed were replaced with direct references to stream->link. This change is technically sound because, by design, these two pointers should always point to the same underlying link object when valid, making the intermediate sink reference redundant and a source of unnecessary risk. By eliminating this indirection layer in DPMS sequences, the code becomes both safer and more efficient. Additionally, an assertion was added during USB4 bandwidth allocation processes where the presence of a sink is strictly required, ensuring that any unexpected null states are caught early with clear diagnostic feedback rather than causing silent corruption or crashes later in execution.
The operational impact of this vulnerability extends beyond simple stability issues; it affects the reliability of display subsystems on systems utilizing AMD graphics hardware. An attacker who can trigger specific display state changes might exploit this flaw to cause a denial of service by crashing the kernel, thereby disrupting all system operations. Furthermore, inconsistent resource access patterns in the original code could lead to subtle race conditions or logic errors if stream->link was accessed multiple times without caching it locally. The fix addresses these inconsistencies by ensuring uniform access patterns and pulling out effective VPG calculations into helper getters, which enhances code maintainability and reduces the attack surface for potential future vulnerabilities related to resource management.
From a defense-in-depth perspective, this remediation aligns with best practices outlined in industry standards such as CWE-476 for null pointer handling and supports robust software engineering principles that emphasize explicit validation of optional data structures. The changes also reflect ATT&CK technique considerations regarding system availability disruption through kernel exploitation. By enforcing strict checks before dereferencing pointers and standardizing access to link objects, the Linux kernel mitigates risks associated with improper resource management. Administrators should ensure their systems are updated with patches containing these fixes to maintain the integrity and stability of display-related operations, particularly in environments where dynamic display configurations or USB4 docking stations are commonly used.