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The vulnerability CVE-2025-39820 resides in the Linux kernel’s Direct Rendering Manager (DRM) driver for the MSM Display Processing Unit (DPU). Specifically, within the `dpu_encoder_needs_modeset` function in the DRM/MSM/DPU encoder management code. This function is responsible for determining if a display mode change is required during atomic updates. It calls `drm_atomic_get_new_connector_state()` to retrieve the new state of a connector from the atomic commit structure. However, according to the DRM core API, this function can return a NULL pointer if the specified connector is not part of the current atomic state transaction. The vulnerable code path did not include a check for this NULL return value before proceeding to dereference the pointer. This omission leads to a NULL pointer dereference when the condition occurs. The defect could be triggered by userspace applications through DRM ioctl calls, such as those handling atomic mode setting, where a crafted commit excludes certain connectors. When the dereference happens, the kernel attempts to access memory at address zero, typically resulting in a kernel panic or system crash, causing denial of service. The issue is localized to the MSM DPU driver and follows a similar pattern already corrected in other functions like dpu_encoder_update_topology. The patch resolves this by adding a conditional null check, ensuring the function safely handles the NULL case, often by returning a default value like false to indicate no modeset is needed, thereby preventing the crash.
Platform: Linux kernel
Version: Not specified
Vulnerability: NULL pointer dereference
Severity: Medium
Date: 09/16/2025
Prediction: Patch applied 09/16/2025
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Check if vulnerable MSM DPU module is loaded lsmod | grep msm_dpu Determine current kernel version uname -r Example vulnerable code snippet before patch: conn_state = drm_atomic_get_new_connector_state(state, connector); // Missing: if (!conn_state) return false; Example patched code: conn_state = drm_atomic_get_new_connector_state(state, connector); if (!conn_state) return false;
How Exploit:
- Craft atomic commit.
- Exclude connector state.
- Trigger kernel panic.
Protection from this CVE
- Apply kernel patch.
- Update kernel version.
- Disable module.
Impact:
- Denial of service.
- System crash.
- Potential instability.
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Sources:
Reported By: nvd.nist.gov
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