CVE-2021-47108: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47108 affects the MediaTek HDMI driver in the Linux kernel. The vulnerability was discovered when it was found that MT8173 does not provide any mtk_hdmi_conf structure, which causes the kernel to crash with a NULL pointer upon entering mtk_hdmi_bridge_mode_valid() function. This occurs when an HDMI cable is plugged in (Kernel Commit).

The vulnerability stems from missing NULL pointer checks in the mtk_hdmi_bridge_mode_valid() function. The issue was introduced by two commits: one that added a check for CEA modes (41ca9caaae0b) and another that added a limit on maximal HDMI mode clock (c91026a938c2). When the MT8173 hardware, which doesn't provide a mtk_hdmi_conf structure, attempts to use this function, it results in a NULL pointer dereference and subsequent kernel crash (Kernel Commit).

When exploited, this vulnerability can cause a kernel crash (denial of service) on systems using the affected MediaTek HDMI driver, specifically when an HDMI cable is connected to systems using the MT8173 chipset (Kernel Commit).

The vulnerability is triggered by a normal hardware operation (plugging in an HDMI cable), making it easily exploitable in systems using the affected hardware configuration (Kernel Commit).

The fix involves adding a NULL pointer check for hdmi->conf in the mtk_hdmi_bridge_mode_valid() function before accessing its members. This patch has been merged into the Linux kernel to restore HDMI functionality and prevent NULL pointer kernel panics (Kernel Commit).