CVE-2026-64050 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/msm/dpu: don't mix devm and drmm functions
Mixing devm and drmm functions will result in a use-after-free on msm driver teardown if userspace keeps a reference on the drm device: The WB connector data will be destroyed because of the use of devm_kzalloc()), while the usersoace still can try interacting with the WB connector (which uses drmm_ functions).
Change dpu_writeback_init() to use drmm_.
Patchwork: https://patchwork.freedesktop.org/patch/722656/
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability represents a critical memory management issue in the Linux kernel's display subsystem, specifically within the msm driver's dpu (Display Processing Unit) component. The flaw arises from improper mixing of device memory management functions that create conflicting cleanup behaviors during driver shutdown sequences. When devm_ and drmm_ functions are used interchangeably within the same code path, it creates a scenario where memory allocated through one mechanism gets freed while references to it remain accessible through another mechanism.
The technical root cause stems from the fundamental differences between devm_kzalloc() and drmm_kzalloc() function behaviors. Device managed memory allocated through devm_ functions is automatically freed when the device is removed, regardless of reference counts or user space interactions. In contrast, drmm_ functions integrate with the DRM subsystem's resource management framework, which maintains cleanup timing based on DRM device reference counting and proper teardown sequences. When these mechanisms are mixed, the memory allocated by devm_kzalloc() gets prematurely freed during driver teardown while userspace continues to hold references to the same DRM device structure, leading to a classic use-after-free condition.
The operational impact of this vulnerability is severe as it allows for potential privilege escalation and system instability. During normal operation, when userspace maintains an active reference to the drm device, the kernel's cleanup process may destroy memory structures that are still being accessed by user space processes. Specifically, the WB (Writeback) connector data structure gets destroyed through devm_kzalloc() while user space can still attempt interactions with this connector that were allocated using drmm_ functions. This mismatch creates a race condition where freed memory can be accessed and potentially corrupted, leading to kernel crashes or arbitrary code execution.
This vulnerability aligns with CWE-416, which addresses Use After Free conditions in software systems, and demonstrates poor resource management practices within the kernel's device driver framework. From an ATT&CK perspective, this flaw could enable privilege escalation techniques through kernel memory corruption, potentially allowing attackers to execute malicious code with kernel privileges. The issue particularly affects systems using Qualcomm's msm display drivers where the dpu subsystem handles graphics processing and display output management.
The recommended mitigation involves implementing a consistent resource management strategy throughout the dpu_writeback_init() function. By changing all allocations within this function to use drmm_ variants instead of devm_ functions, the cleanup behavior becomes properly synchronized with the DRM subsystem's reference counting mechanisms. This ensures that memory allocated for the WB connector and related structures remains valid for as long as user space maintains references to the DRM device, preventing premature deallocation during driver teardown. The patch resolution addresses this by ensuring all memory management within the initialization function uses the same resource management framework, eliminating the conflicting cleanup behaviors that led to the vulnerability.
The fix demonstrates proper kernel driver development practices where resource management consistency is maintained throughout the entire driver lifecycle. This approach prevents similar issues in other parts of the DRM subsystem and reinforces the principle that mixing different memory management frameworks within the same code path can lead to subtle but critical timing issues during system shutdown or cleanup operations. The vulnerability highlights the importance of understanding the specific semantics and cleanup behaviors of different kernel memory allocation functions when developing device drivers, particularly those integrating with complex subsystems like DRM that manage their own reference counting and resource cleanup processes.