CVE-2026-89802 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/nouveau/uvmm: fix NULL deref unwinding an OP_MAP_SPARSE op
Each bind_job_op is zeroed by kzalloc_obj() in bind_job_op_from_uop(), and the OP_MAP_SPARSE case in nouveau_uvmm_bind_job_submit() only creates a region, so op->ops stays NULL for a successfully processed sparse map.
If a later op in the same job fails, the reverse unwind loop revisits that op and calls drm_gpuva_ops_free(&uvmm->base, op->ops) unconditionally. drm_gpuva_ops_free() dereferences its argument right away (list_for_each_entry_safe on &ops->list), so a NULL op->ops oopses. The path is reachable by any render-node fd holder, since NOUVEAU_VM_BIND is DRM_RENDER_ALLOW.
Guard the free with IS_ERR_OR_NULL(), as nouveau_uvmm_bind_job_cleanup() already does for the identical free.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in the Linux kernel's Nouveau driver involves a NULL pointer dereference that occurs during the unwinding phase of job submission operations within the Unified Virtual Memory Management (UVMM) subsystem. This specific flaw is triggered when processing an OP_MAP_SPARSE operation, which is designed to map sparse memory regions for GPU virtual address management. The root cause lies in the initialization and subsequent cleanup logic of bind_job_op structures. When a new operation object is allocated via kzalloc_obj(), it is zeroed out, ensuring that all fields including op->ops are initially set to NULL. For successful OP_MAP_SPARSE operations, no actual ops list is created because sparse mapping does not require standard GPU virtual address range tracking in the same way as other map types. Consequently, op->ops remains NULL after a successful sparse map operation completes within a job sequence.
The critical failure occurs when a subsequent operation within the same job fails and triggers an error handling routine that performs reverse unwinding of previously submitted operations. During this cleanup phase, the kernel attempts to free resources associated with earlier operations in the chain. The function drm_gpuva_ops_free is called unconditionally on every op encountered during this unwind process without verifying whether the ops pointer was actually populated. Since drm_gpu_va_ops_free immediately dereferences its argument by iterating over &ops->list using list_for_each_entry_safe, passing a NULL pointer results in an immediate kernel oops or panic. This represents a classic null pointer dereference vulnerability where error handling logic assumes data structures are fully initialized even when they were intentionally left empty due to the nature of sparse memory mapping.
From a security perspective, this vulnerability is particularly concerning because it affects render nodes which have broader access privileges compared to other device interfaces. The NOUVEAU_VM_BIND ioctl command carries the DRM_RENDER_ALLOW flag, meaning that any user space process with access to a render node file descriptor can trigger this code path by submitting GPU jobs containing mixed operation types where sparse mapping precedes an operation that fails later in the sequence. This accessibility makes the vulnerability exploitable by unprivileged users who have been granted standard graphics device permissions, potentially leading to local denial of service conditions through kernel crashes or system instability. The impact is primarily availability-focused as it causes immediate kernel panic rather than allowing arbitrary code execution or information disclosure directly through this specific flaw vector.
The technical classification for this issue aligns with CWE-476 which describes NULL pointer dereference vulnerabilities where software fails to check a pointer before using it, leading to crashes when the pointer is unexpectedly null. In terms of attack patterns, this relates to improper input validation and error handling mechanisms within kernel subsystems that process complex multi-step operations. The vulnerability exploits the assumption that all operation objects will have valid ops lists regardless of their type or success status during initial processing phases. This oversight in defensive programming practices allows a sequence of legitimate but mixed-type GPU commands to trigger catastrophic failure when later steps encounter errors requiring rollback procedures.
Mitigation strategies involve applying the upstream kernel patch which guards the drm_gpuva_ops_free call with an IS_ERR_OR_NULL check before attempting to dereference the ops pointer. This ensures that only operations that actually allocated resources are cleaned up during error unwinding sequences, preventing access to uninitialized memory structures. System administrators should ensure their systems run patched versions of the Linux kernel containing this fix for the Nouveau driver UVMM subsystem. For environments where immediate patching is not possible, restricting render node access through strict DAC permissions or SELinux policies can reduce exposure by limiting which users can submit GPU jobs that might trigger this code path until a permanent solution is deployed across all affected systems.