CVE-2026-80888 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/vmwgfx: drop dma_buf reference on foreign-fd prime import
ttm_prime_fd_to_handle() returns -ENOSYS when the imported fd's dma_buf->ops do not match the ttm_object_device's ops, but does so without releasing the reference acquired by dma_buf_get(). Any unprivileged renderD client passing a non-vmwgfx prime fd through the DRM_VMW_GB_SURFACE_REF{,_EXT} path leaks one dma_buf reference per
call and indefinitely pins the foreign exporter's GEM resources.
Funnel the error path through the existing dma_buf_put() so the reference is always dropped.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in the Linux kernel involves a resource management flaw within the VMware graphics driver, specifically affecting the vmwgfx subsystem. This issue arises during the process of importing buffer objects via prime file descriptors using the ttm_prime_fd_to_handle function. The core technical failure lies in an error handling path where a reference count for a dma_buf object is acquired but not subsequently released under certain conditions. When an unprivileged user space client attempts to import a foreign file descriptor that does not match the expected operations of the device, the kernel returns an ENOSYS error code indicating unsupported functionality. However, despite this failure, the previously incremented reference count on the imported dma_buf remains unreleased. This oversight constitutes a classic resource leak vulnerability where system resources are consumed without being properly returned to the pool for reuse or deallocation.
From a technical perspective, the flaw is rooted in the asymmetry between acquiring and releasing references to kernel objects. The function dma_buf_get increments the reference count to ensure the buffer object remains valid during processing. In successful execution paths, this reference is correctly balanced by a corresponding call to dma_buf_put upon completion of operations such as surface creation or modification via DRM_VMW_GB_SURFACE_REF extensions. However, in error scenarios where the imported file descriptor's associated dma_buf_ops do not align with those expected by the ttm_object_device, the code path exits prematurely without invoking the cleanup routine. This results in a persistent hold on the foreign exporter’s Graphics Execution Manager resources. Over time, repeated invocations of this flawed sequence lead to an accumulation of unreleased references, effectively pinning these memory objects and preventing their deallocation even after they are no longer actively used by the application or system.
The operational impact of this vulnerability is significant for both system stability and security posture. Primarily, it leads to a steady depletion of kernel memory resources as each failed import attempt consumes one dma_buf reference indefinitely. This can result in gradual performance degradation due to increased pressure on the memory subsystem and potential exhaustion of available buffer handles. More critically, by pinning foreign GEM resources, the vulnerability allows an unprivileged user space process to indirectly deny service to other processes or system components that rely on those pinned buffers. While this does not directly grant privilege escalation, it facilitates a local denial-of-service condition where legitimate applications may fail due to resource contention caused by leaked handles. The ability of any renderD client to trigger this leak means the attack surface is relatively broad for users with access to graphical rendering interfaces.
In terms of industry classification standards, this vulnerability aligns closely with CWE-401, which describes a missing release of memory after successful allocation leading to resource exhaustion. It also relates to CWE-755, concerning improper handling of unusual or exceptional input conditions where error paths fail to clean up state properly. From an adversarial tactics perspective, the exploitation pattern corresponds to ATT&CK technique T1496, Resource Hijacking, specifically through environmental hijacking by consuming system resources like memory handles to degrade performance or availability for other processes. The vulnerability highlights a common class of bugs in kernel drivers where error handling logic is not fully synchronized with resource acquisition logic during complex object lifecycles involving external file descriptors and buffer management subsystems.
Mitigation strategies focus on ensuring that all code paths, including those leading to early returns due to validation failures, properly balance reference counts acquired earlier in the execution flow. The resolution involves funneling the error path through the existing dma_buf_put function call so that the reference is always dropped regardless of whether the import operation succeeds or fails based on compatibility checks. Developers must audit similar patterns across other kernel drivers to identify and patch analogous leaks where resource acquisition precedes validation steps without corresponding cleanup in failure branches. System administrators should apply updated kernel packages containing this fix immediately to prevent potential denial-of-service conditions arising from sustained exploitation by local unprivileged users interacting with the VMware graphics stack.