CVE-2026-89816 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm: Fix drm_crtc_commit leak if signaled when PAGE_FLIP_EVENT is used
Commit 1c6ceeee6ebb ("drm/atomic: Fix memleak on ERESTARTSYS during non-blocking commits") fixed a very similar issue when the event was allocated by drm_atomic_helper_setup_commit() itself.
However, if the event is allocated in prepare_signaling(), it will also be set to NULL in complete_signaling(), which prevents drm_crtc_commit from being put in __drm_atomic_helper_crtc_destroy_state().
Dropping the reference when the event is set to NULL at complete_signaling() fixes the leak.
The leak can be reproduced by sending a signal to the thread using DRM_MODE_PAGE_FLIP_EVENT and using a sw_sync fence to cause the atomic ioctl to block at drm_atomic_helper_wait_for_fences(). It happened both with amdgpu and vkms.
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Analysis
by VulDB Data Team • 09/16/2026
This vulnerability represents a memory leak within the Linux kernel's Direct Rendering Manager subsystem, specifically affecting the handling of asynchronous page flip events during atomic mode setting operations. The issue arises from an imbalance in reference counting for drm_crtc_commit structures when specific signaling conditions are met. While previous patches addressed similar leaks occurring during non-blocking commits where the event was allocated by drm_atomic_helper_setup_commit(), this particular flaw targets scenarios where the event is allocated within prepare_signaling(). In these cases, if the operation encounters a signal or error condition that triggers complete_signaling(), the associated event pointer is set to NULL. This nullification inadvertently prevents the subsequent call to __drm_atomic_helper_crtc_destroy_state() from properly invoking drm_crtc_commit_put(), thereby leaving the commit structure unreleased and causing a persistent memory leak in kernel space.
The technical root cause lies in the lifecycle management of synchronization objects within the atomic DRM framework. When an application requests a page flip with the DRM_MODE_PAGE_FLIP_EVENT flag, the kernel allocates resources to track the completion of this operation via software sync fences. If the process handling the ioctl is interrupted by a signal while waiting for these fences at drm_atomic_helper_wait_for_fences(), the cleanup path in complete_signaling() nullifies the event pointer. Because __drm_atomic_helper_crtc_destroy_state() relies on checking whether an event exists to decide whether to release the commit object, this premature nullification breaks the reference counting logic. Consequently, every instance of a signaled interruption during such operations results in leaked kernel memory that is not reclaimed until system reboot or module unload, potentially leading to resource exhaustion under high-frequency usage patterns involving amdgpu or vkms drivers.
From an operational impact perspective, this vulnerability allows for local denial-of-service through resource consumption. Although the leak per instance may be small, repeated exploitation by a malicious user space process can gradually deplete kernel memory pools. This degradation in system stability could eventually lead to out-of-memory conditions affecting other critical subsystems or cause the kernel to invoke its oom killer indiscriminately. The vulnerability is particularly relevant for systems running graphics-intensive workloads where page flips occur frequently, such as desktop environments with compositors or gaming applications utilizing Vulkan and AMDGPU drivers. It does not provide privilege escalation but undermines system reliability by eroding available memory resources over time through sustained interaction with the DRM subsystem.
Mitigation strategies primarily involve applying the upstream kernel patch that corrects the reference counting logic in complete_signaling(). System administrators should ensure their Linux kernels are updated to versions containing this fix, which properly handles the release of drm_crtc_commit references even when events are nullified due to signal interruptions. For environments where immediate patching is not feasible, limiting the frequency of page flip operations or avoiding applications that trigger non-blocking atomic commits with event signaling can reduce exposure risk. Additionally, monitoring kernel memory usage for anomalies in systems running affected drivers like amdgpu and vkms may help detect early signs of exploitation attempts characterized by gradual but steady increases in untracked kernel allocations associated with DRM structures.
This vulnerability is categorized under CWE-401, which describes a missing release of memory after effective use, highlighting the failure to properly deallocate resources during error or signal handling paths. In terms of adversarial tactics, it aligns with ATT&CK technique T1529, System Shutdown/Reboot, as an attacker could theoretically leverage this leak to degrade system availability by forcing repeated reboots due to memory exhaustion. The fix ensures that the kernel maintains strict adherence to reference counting principles regardless of whether the signaling event is successfully delivered or interrupted, thereby preserving the integrity and stability of the graphics subsystem under adverse conditions.