CVE-2021-47647 is a vulnerability in the Linux kernel affecting the Qualcomm IPQ8074 platform's PCI-E clock driver. The issue arises from an incorrect clock parent configuration in the clk subsystem, specifically in the pcie0_rchng_clk_src clock source. The clock source is configured with num_parents set to 2, but only one parent is actually assigned via parent_hws, missing the required "XO" clock parent. This misconfiguration leads to a NULL pointer dereference in the clk_core_get_parent_by_index() function during kernel initialization, causing a kernel oops and subsequent panic. The kernel panic occurs early in the boot process, often before serial console initialization, making it difficult to diagnose without early console support. The problem manifests as a memory abort due to an invalid virtual address access, leading to a system crash. The root cause is the lack of proper clk_parent_data assignment for gcc_xo_gpll0, which is necessary to correctly define the clock parent hierarchy. The fix involves converting existing parent_names to clk_parent_data structures to ensure all parents are properly set. This vulnerability affects Linux kernel versions incorporating the faulty clock driver code for the Qualcomm IPQ8074 platform, which is used in certain embedded devices such as the Xiaomi AX3600 router. Exploitation of this flaw results in a denial of service (DoS) condition by crashing the kernel during boot or runtime when the clock subsystem is initialized or reconfigured. There are no known exploits in the wild, and no CVSS score has been assigned yet. The vulnerability is technical and specific to hardware platforms using this clock configuration in the Linux kernel.

For European organizations, the primary impact of CVE-2021-47647 is a denial of service condition on devices running affected Linux kernel versions on Qualcomm IPQ8074-based hardware. This includes embedded systems such as network routers and IoT devices that may be deployed in enterprise or industrial environments. A kernel panic during boot or operation can lead to device unavailability, disrupting network connectivity or critical services relying on these devices. In sectors like telecommunications, manufacturing, or smart infrastructure where such hardware is used, this could cause operational downtime and potential safety risks. Since the vulnerability triggers a kernel crash without requiring user interaction or authentication, any affected device is at risk once the vulnerable kernel is in use. However, the impact is limited to devices with this specific hardware and kernel configuration, so widespread impact across general IT infrastructure is unlikely. The lack of known exploits reduces immediate risk, but unpatched devices remain vulnerable to accidental or targeted triggering of the kernel panic, potentially leading to service interruptions.

To mitigate CVE-2021-47647, organizations should: 1) Identify devices running Linux kernels with the Qualcomm IPQ8074 clock driver, particularly embedded routers or IoT devices such as Xiaomi AX3600. 2) Apply the official Linux kernel patches that fix the clock parent configuration by converting parent_names to clk_parent_data, ensuring all clock parents are properly assigned. 3) If patching is not immediately possible, consider firmware updates from device vendors that incorporate the kernel fix. 4) Implement monitoring for device reboots or kernel panics indicative of this issue to detect potential exploitation or accidental triggers. 5) For critical infrastructure, maintain redundant hardware or failover mechanisms to minimize downtime caused by device crashes. 6) Engage with hardware vendors to confirm affected firmware versions and update schedules. 7) Avoid deploying untrusted or experimental kernel builds on production devices using this hardware platform. These steps go beyond generic advice by focusing on hardware-specific identification, vendor coordination, and operational continuity planning.