CVE-2026-89828 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: Fix init ordering in amdgpu_vram_mgr_init()
drmm_cgroup_register_region() is called before INIT_LIST_HEAD() and gpu_buddy_init() in amdgpu_vram_mgr_init(). If it fails, the function returns early and bypasses those initializations.
Since adev->mman.initialized is set to true before amdgpu_vram_mgr_init() is called, a failure triggers amdgpu_ttm_fini(), which calls amdgpu_vram_mgr_fini(), which then:
- Calls list_for_each_entry_safe() on reservations_pending and reserved_pages, whose list_head::next pointers are zero-initialized (NULL). The loop does not recognize them as empty and dereferences NULL.
- Calls gpu_buddy_fini(), which iterates free_trees[] unconditionally
via for_each_free_tree(). Since mm->free_trees is NULL (never allocated), this dereferences NULL.
Both result in a kernel panic on the module load error path.
Fix by moving drmm_cgroup_register_region() to after the list and buddy allocator are fully initialized, so the teardown path is safe to run.
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Analysis
by VulDB Data Team • 09/16/2026
The identified vulnerability resides within the Linux kernel's AMDGPU driver subsystem, specifically in the initialization routine amdgpu_vram_mgr_init(). This function manages video memory allocation for AMD graphics processing units. The core technical flaw stems from an incorrect ordering of operations during the device setup phase. Specifically, the call to drmm_cgroup_register_region() is executed before the critical data structures reservations_pending and reserved_pages are initialized via INIT_LIST_HEAD(), as well as before gpu_buddy_init() allocates memory for free_trees. This sequencing error creates a dangerous state where if the cgroup registration fails, the function returns early without completing these essential initializations.
The operational impact of this flaw is severe because it triggers an unhandled kernel panic during module load failure scenarios. The root cause lies in how the driver handles cleanup when initialization fails. Since the flag adev->mman.initialized is set to true prior to calling amdgpu_vram_mgr_init(), any subsequent error causes the system to invoke amdgpu_ttm_fini(). This teardown function subsequently calls amdgpu_vram_mgr_fini() to clean up resources. However, because the initialization was incomplete due to the early return, the data structures remain in an invalid state. The cleanup routine attempts to iterate over reservations_pending and reserved_pages using list_for_each_entry_safe(), but since these lists were never initialized with valid head pointers, their next fields are zero-initialized or NULL. The loop logic fails to recognize them as empty and proceeds to dereference a NULL pointer, resulting in a crash.
A similar null pointer dereference occurs within the gpu_buddy_fini() function called during teardown. This routine iterates over free_trees[] using for_each_free_tree(). Because gpu_buddy_init() was bypassed due to the earlier failure, mm->free_trees remains NULL and was never allocated. The unconditional iteration attempts to access this null memory region, leading directly to a kernel panic. These issues represent classic initialization-ordering vulnerabilities where error handling paths assume resources are fully prepared for destruction even when setup did not complete successfully.
From a security classification perspective, this vulnerability aligns with CWE-672, which describes the use of operationally unnecessary or incorrect operations that can lead to unexpected behavior and potential denial of service. The specific mechanism involves improper initialization leading to null pointer dereference during error handling paths. In terms of adversary tactics, while primarily affecting system stability rather than direct exploitation for privilege escalation in this context, it relates to ATT&CK technique T1499, Endpoint Denial of Service, as the vulnerability allows an attacker or faulty hardware state to crash the operating system by triggering a module load failure path that was not robustly coded.
The remediation strategy involves reordering the initialization sequence within amdgpu_vram_mgr_init(). By moving the drmm_cgroup_register_region() call to occur after both list heads have been initialized via INIT_LIST_HEAD and the buddy allocator has been set up through gpu_buddy_init, the driver ensures that all resources required for cleanup are valid. This guarantees that if an error occurs later in the process or during teardown, the amdgpu_vram_mgr_fini() routine will operate on properly allocated and linked data structures rather than null pointers. This fix restores robustness to the module load failure path, preventing kernel panics and ensuring system stability even when hardware initialization encounters issues.