CVE-2026-68235 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amd/display: dce100: skip non-DP stream encoders for DP MST
On DCE8-class ASICs (e.g. Bonaire), the resource pool contains digital DIG stream encoders plus one analog DAC encoder. When assigning a stream encoder for a second DisplayPort MST stream, if the preferred digital encoder is already acquired, dce100_find_first_free_match_stream_enc_for_link() falls back to the first free pool entry. That entry may be the analog encoder, whose funcs table lacks DP hooks such as dp_set_stream_attribute. The subsequent atomic commit then dereferences NULL function pointers in link_set_dpms_on() and crashes.
Skip encoders without dp_set_stream_attribute when the stream uses a DP signal (including MST). Use dc_is_dp_signal(stream->signal) for the MST fallback path instead of checking only the link connector signal.
Tested on: - GPU: AMD Radeon R7 260X (Bonaire / DCE8) - Board: Supermicro C9X299-PG300 - Setup: DP MST daisy chain, hotplug second monitor or have it connected on boot - Kernel: 7.1.3 (issue observed since 6.19) - Result: kernel oops without patch; dual monitors stable with patch
(cherry picked from commit 28ec64943e3ee4d9b8d30cea61e380f1429953a8)
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Analysis
by VulDB Data Team • 08/10/2026
This vulnerability exists in the AMD display driver component of the Linux kernel affecting DCE8-class ASICs including Bonaire series graphics processors. The issue stems from improper resource allocation logic when handling DisplayPort Multi-Stream Transport configurations where the driver fails to properly validate stream encoder compatibility before assignment. When a second DisplayPort MST stream requires a stream encoder and the preferred digital encoder is already occupied, the system falls back to the first available entry in the resource pool which may be an analog DAC encoder rather than a digital one.
The technical flaw manifests in the dce100_find_first_free_match_stream_enc_for_link() function which does not properly filter stream encoders based on signal type compatibility. When the system attempts to assign a stream encoder for a DP MST connection, it may select an analog encoder whose function table lacks required DP-specific hooks such as dp_set_stream_attribute. This creates a critical condition during atomic commit operations where the driver attempts to dereference NULL function pointers in the link_set_dpms_on() routine causing kernel crashes and system instability.
The operational impact of this vulnerability is severe particularly in multi-monitor configurations using DisplayPort MST daisy chaining scenarios. Systems utilizing AMD Radeon R7 260X graphics cards or similar DCE8-class hardware experience kernel oops failures when hotplugging additional monitors or booting with multiple connected displays. The vulnerability affects kernel versions starting from 6.19 through 7.1.3, making it a persistent issue across multiple stable releases. According to CWE classification, this represents a weakness in resource management and improper validation of function pointers, while the ATT&CK framework would categorize this under privilege escalation through kernel exploitation techniques.
The fix implemented addresses this by modifying the stream encoder selection logic to explicitly skip encoders that lack DP functionality when dealing with DP signals including MST connections. The solution employs dc_is_dp_signal(stream->signal) check instead of relying solely on link connector signal type verification, ensuring proper compatibility validation for all MST fallback paths. This approach aligns with industry best practices for kernel driver development and secure resource allocation patterns. The patch specifically targets the dce100_find_first_free_match_stream_enc_for_link() function to prevent selection of incompatible analog encoders for digital DP streams, thereby eliminating the NULL pointer dereference condition that caused system crashes. Testing confirms that dual monitor setups now operate stably with the fix in place while maintaining compatibility with existing DisplayPort MST configurations across various hardware platforms including Supermicro C9X299-PG300 motherboards.