CVE-2024-40916: Vulnerability in Linux Linux

Severity: mediumType: vulnerabilityCVE-2024-40916

In the Linux kernel, the following vulnerability has been resolved: drm/exynos: hdmi: report safe 640x480 mode as a fallback when no EDID found When reading EDID fails and driver reports no modes available, the DRM core adds an artificial 1024x786 mode to the connector. Unfortunately some variants of the Exynos HDMI (like the one in Exynos4 SoCs) are not able to drive such mode, so report a safe 640x480 mode instead of nothing in case of the EDID reading failure. This fixes the following issue observed on Trats2 board since commit 13d5b040363c ("drm/exynos: do not return negative values from .get_modes()"): [drm] Exynos DRM: using 11c00000.fimd device for DMA mapping operations exynos-drm exynos-drm: bound 11c00000.fimd (ops fimd_component_ops) exynos-drm exynos-drm: bound 12c10000.mixer (ops mixer_component_ops) exynos-dsi 11c80000.dsi: [drm:samsung_dsim_host_attach] Attached s6e8aa0 device (lanes:4 bpp:24 mode-flags:0x10b) exynos-drm exynos-drm: bound 11c80000.dsi (ops exynos_dsi_component_ops) exynos-drm exynos-drm: bound 12d00000.hdmi (ops hdmi_component_ops) [drm] Initialized exynos 1.1.0 20180330 for exynos-drm on minor 1 exynos-hdmi 12d00000.hdmi: [drm:hdmiphy_enable.part.0] *ERROR* PLL could not reach steady state panel-samsung-s6e8aa0 11c80000.dsi.0: ID: 0xa2, 0x20, 0x8c exynos-mixer 12c10000.mixer: timeout waiting for VSYNC ------------[ cut here ]------------ WARNING: CPU: 1 PID: 11 at drivers/gpu/drm/drm_atomic_helper.c:1682 drm_atomic_helper_wait_for_vblanks.part.0+0x2b0/0x2b8 [CRTC:70:crtc-1] vblank wait timed out Modules linked in: CPU: 1 PID: 11 Comm: kworker/u16:0 Not tainted 6.9.0-rc5-next-20240424 #14913 Hardware name: Samsung Exynos (Flattened Device Tree) Workqueue: events_unbound deferred_probe_work_func Call trace: unwind_backtrace from show_stack+0x10/0x14 show_stack from dump_stack_lvl+0x68/0x88 dump_stack_lvl from __warn+0x7c/0x1c4 __warn from warn_slowpath_fmt+0x11c/0x1a8 warn_slowpath_fmt from drm_atomic_helper_wait_for_vblanks.part.0+0x2b0/0x2b8 drm_atomic_helper_wait_for_vblanks.part.0 from drm_atomic_helper_commit_tail_rpm+0x7c/0x8c drm_atomic_helper_commit_tail_rpm from commit_tail+0x9c/0x184 commit_tail from drm_atomic_helper_commit+0x168/0x190 drm_atomic_helper_commit from drm_atomic_commit+0xb4/0xe0 drm_atomic_commit from drm_client_modeset_commit_atomic+0x23c/0x27c drm_client_modeset_commit_atomic from drm_client_modeset_commit_locked+0x60/0x1cc drm_client_modeset_commit_locked from drm_client_modeset_commit+0x24/0x40 drm_client_modeset_commit from __drm_fb_helper_restore_fbdev_mode_unlocked+0x9c/0xc4 __drm_fb_helper_restore_fbdev_mode_unlocked from drm_fb_helper_set_par+0x2c/0x3c drm_fb_helper_set_par from fbcon_init+0x3d8/0x550 fbcon_init from visual_init+0xc0/0x108 visual_init from do_bind_con_driver+0x1b8/0x3a4 do_bind_con_driver from do_take_over_console+0x140/0x1ec do_take_over_console from do_fbcon_takeover+0x70/0xd0 do_fbcon_takeover from fbcon_fb_registered+0x19c/0x1ac fbcon_fb_registered from register_framebuffer+0x190/0x21c register_framebuffer from __drm_fb_helper_initial_config_and_unlock+0x350/0x574 __drm_fb_helper_initial_config_and_unlock from exynos_drm_fbdev_client_hotplug+0x6c/0xb0 exynos_drm_fbdev_client_hotplug from drm_client_register+0x58/0x94 drm_client_register from exynos_drm_bind+0x160/0x190 exynos_drm_bind from try_to_bring_up_aggregate_device+0x200/0x2d8 try_to_bring_up_aggregate_device from __component_add+0xb0/0x170 __component_add from mixer_probe+0x74/0xcc mixer_probe from platform_probe+0x5c/0xb8 platform_probe from really_probe+0xe0/0x3d8 really_probe from __driver_probe_device+0x9c/0x1e4 __driver_probe_device from driver_probe_device+0x30/0xc0 driver_probe_device from __device_attach_driver+0xa8/0x120 __device_attach_driver from bus_for_each_drv+0x80/0xcc bus_for_each_drv from __device_attach+0xac/0x1fc __device_attach from bus_probe_device+0x8c/0x90 bus_probe_device from deferred_probe_work_func+0 ---truncated---

AI Analysis

Technical Summary

CVE-2024-40916 is a vulnerability in the Linux kernel's Direct Rendering Manager (DRM) subsystem, specifically affecting the Exynos HDMI driver used in certain Samsung Exynos System on Chips (SoCs). The issue arises when the Extended Display Identification Data (EDID) reading fails. Normally, when no EDID is found, the DRM core artificially adds a 1024x768 resolution mode to the connector as a fallback. However, some Exynos HDMI variants, such as those in Exynos4 SoCs, cannot support this mode, leading to failures in display initialization and potentially causing system instability or degraded functionality. The fix implemented changes the fallback mode to a safe 640x480 resolution instead of the unsupported 1024x768, preventing the HDMI driver from attempting to drive an unsupported mode. This vulnerability manifests as errors during HDMI initialization, including PLL (Phase-Locked Loop) failures to reach a steady state, VSYNC timeouts, and warnings in the kernel logs related to DRM atomic helper functions. These errors can cause the display subsystem to malfunction, potentially resulting in system crashes or degraded graphical output. The vulnerability was introduced around commit 13d5b040363c and affects multiple Linux kernel versions prior to the patch. While no known exploits are currently reported in the wild, the issue impacts the stability and reliability of devices using affected Exynos SoCs with HDMI output, particularly in embedded or mobile environments relying on Linux kernel DRM drivers.

Potential Impact

For European organizations, the impact of CVE-2024-40916 primarily concerns entities deploying embedded systems, industrial devices, or mobile platforms based on affected Samsung Exynos SoCs running Linux. This includes sectors such as telecommunications, automotive, industrial automation, and consumer electronics manufacturers or integrators. The vulnerability can lead to display failures or system instability, which may disrupt critical operations, especially in environments where reliable visual output is essential (e.g., control panels, digital signage, or infotainment systems). Although it does not directly expose confidentiality or integrity risks, the availability and operational reliability of affected devices can be compromised. This may result in increased maintenance costs, downtime, or degraded user experience. Given the widespread use of Linux in embedded systems across Europe, organizations relying on Exynos-based hardware should assess their exposure. The lack of known exploits reduces immediate risk, but the potential for denial-of-service conditions or hardware malfunctions warrants timely remediation to maintain operational continuity.

Mitigation Recommendations

Organizations should take the following specific actions to mitigate CVE-2024-40916: 1) Identify all devices and systems using Samsung Exynos SoCs with HDMI output running vulnerable Linux kernel versions. 2) Apply the official Linux kernel patches that modify the fallback HDMI mode from 1024x768 to 640x480, ensuring the kernel version includes the fix introduced after commit 13d5b040363c. 3) For embedded or custom Linux distributions, rebuild and redeploy the kernel with the patched DRM/exynos HDMI driver. 4) Test affected devices post-patch to verify stable HDMI initialization and display functionality. 5) Monitor kernel logs for DRM-related errors or warnings indicating HDMI initialization issues. 6) Where patching is not immediately feasible, consider hardware workarounds such as ensuring EDID data is reliably available or disabling HDMI output if not required. 7) Engage with hardware vendors or system integrators to confirm updated firmware or kernel versions addressing this issue. 8) Incorporate this vulnerability into vulnerability management and patching schedules to ensure ongoing compliance and risk reduction.