CVE-2022-50256 in Linux
Summary
by MITRE • 09/15/2025
In the Linux kernel, the following vulnerability has been resolved:
drm/meson: remove drm bridges at aggregate driver unbind time
drm bridges added by meson_encoder_hdmi_init and meson_encoder_cvbs_init were not manually removed at module unload time, which caused dangling references to freed memory to remain linked in the global bridge_list.
When loading the driver modules back in, the same functions would again call drm_bridge_add, and when traversing the global bridge_list, would end up peeking into freed memory.
Once again KASAN revealed the problem:
[ +0.000095] =============================================================
[ +0.000008] BUG: KASAN: use-after-free in __list_add_valid+0x9c/0x120
[ +0.000018] Read of size 8 at addr ffff00003da291f0 by task modprobe/2483
[ +0.000018] CPU: 3 PID: 2483 Comm: modprobe Tainted: G C O 5.19.0-rc6-lrmbkasan+ #1
[ +0.000011] Hardware name: Hardkernel ODROID-N2Plus (DT)
[ +0.000008] Call trace:
[ +0.000006] dump_backtrace+0x1ec/0x280
[ +0.000012] show_stack+0x24/0x80
[ +0.000008] dump_stack_lvl+0x98/0xd4
[ +0.000011] print_address_description.constprop.0+0x80/0x520
[ +0.000011] print_report+0x128/0x260
[ +0.000008] kasan_report+0xb8/0xfc
[ +0.000008] __asan_report_load8_noabort+0x3c/0x50
[ +0.000009] __list_add_valid+0x9c/0x120
[ +0.000009] drm_bridge_add+0x6c/0x104 [drm]
[ +0.000165] dw_hdmi_probe+0x1900/0x2360 [dw_hdmi]
[ +0.000022] meson_dw_hdmi_bind+0x520/0x814 [meson_dw_hdmi]
[ +0.000014] component_bind+0x174/0x520
[ +0.000012] component_bind_all+0x1a8/0x38c
[ +0.000010] meson_drv_bind_master+0x5e8/0xb74 [meson_drm]
[ +0.000032] meson_drv_bind+0x20/0x2c [meson_drm]
[ +0.000027] try_to_bring_up_aggregate_device+0x19c/0x390
[ +0.000010] component_master_add_with_match+0x1c8/0x284
[ +0.000009] meson_drv_probe+0x274/0x280 [meson_drm]
[ +0.000026] platform_probe+0xd0/0x220
[ +0.000009] really_probe+0x3ac/0xa80
[ +0.000009] __driver_probe_device+0x1f8/0x400
[ +0.000009] driver_probe_device+0x68/0x1b0
[ +0.000009] __driver_attach+0x20c/0x480
[ +0.000008] bus_for_each_dev+0x114/0x1b0
[ +0.000009] driver_attach+0x48/0x64
[ +0.000008] bus_add_driver+0x390/0x564
[ +0.000009] driver_register+0x1a8/0x3e4
[ +0.000009] __platform_driver_register+0x6c/0x94
[ +0.000008] meson_drm_platform_driver_init+0x3c/0x1000 [meson_drm]
[ +0.000027] do_one_initcall+0xc4/0x2b0
[ +0.000011] do_init_module+0x154/0x570
[ +0.000011] load_module+0x1a78/0x1ea4
[ +0.000008] __do_sys_init_module+0x184/0x1cc
[ +0.000009] __arm64_sys_init_module+0x78/0xb0
[ +0.000009] invoke_syscall+0x74/0x260
[ +0.000009] el0_svc_common.constprop.0+0xcc/0x260
[ +0.000008] do_el0_svc+0x50/0x70
[ +0.000007] el0_svc+0x68/0x1a0
[ +0.000012] el0t_64_sync_handler+0x11c/0x150
[ +0.000008] el0t_64_sync+0x18c/0x190
[ +0.000016] Allocated by task 879:
[ +0.000008] kasan_save_stack+0x2c/0x5c
[ +0.000011] __kasan_kmalloc+0x90/0xd0
[ +0.000007] __kmalloc+0x278/0x4a0
[ +0.000011] mpi_resize+0x13c/0x1d0
[ +0.000011] mpi_powm+0xd24/0x1570
[ +0.000009] rsa_enc+0x1a4/0x30c
[ +0.000009] pkcs1pad_verify+0x3f0/0x580
[ +0.000009] public_key_verify_signature+0x7a8/0xba4
[ +0.000010] public_key_verify_signature_2+0x40/0x60
[ +0.000008] verify_signature+0xb4/0x114
[ +0.000008] pkcs7_validate_trust_one.constprop.0+0x3b8/0x574
[ +0.000009] pkcs7_validate_trust+0xb8/0x15c
[ +0.000008] verify_pkcs7_message_sig+0xec/0x1b0
[ +0.000012] verify_pkcs7_signature+0x78/0xac
[ +0.000007] mod_verify_sig+0x110/0x190
[ +0.000009] module_sig_check+0x114/0x1e0
[ +0.000009] load_module+0xa0/0x1ea4
[ +0.000008] __do_sys_init_module+0x184/0x1cc
[ +0.000008] __arm64_sys_init_module+0x78/0xb0
[ +0.000008] invoke_syscall+0x74/0x260
[ +0.000009] el0_svc_common.constprop.0+0x1a8/0x260
[ +0.000008] do_el0_svc+0x50/0x70
[ +0.000007] el0_svc+0x68/0x1a0
[ +0.000009] el0t_64_sync_handler+0x11c/0x150
[ +0.000009] el0t_64
---truncated---
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Analysis
by VulDB Data Team • 01/10/2026
The vulnerability described in CVE-2022-50256 resides within the Linux kernel's graphics driver subsystem, specifically affecting the meson drm driver. This issue stems from improper cleanup of drm bridge objects during driver module unloading, leading to use-after-free conditions that can result in system instability or potential exploitation. The flaw manifests when the meson_encoder_hdmi_init and meson_encoder_cvbs_init functions create drm bridge objects that are not explicitly removed during module unload operations. These bridges remain linked in the global bridge_list data structure, creating dangling references to freed memory locations. When the driver modules are reloaded, the same initialization functions attempt to add new bridge objects to the global list while simultaneously traversing the corrupted list, resulting in memory access violations that KASAN (Kernel Address Sanitizer) detects and reports.
The technical execution of this vulnerability involves a classic use-after-free pattern where memory is accessed after being freed, specifically within the drm_bridge_add function which attempts to traverse the global bridge_list. The call trace demonstrates that the error occurs during module loading when dw_hdmi_probe calls meson_dw_hdmi_bind, which then invokes drm_bridge_add, ultimately triggering the use-after-free in __list_add_valid. This pattern represents a fundamental memory management error that violates standard kernel programming practices and can be categorized under CWE-416 as Use After Free. The vulnerability is particularly concerning because it operates at the kernel level where such flaws can lead to privilege escalation or system crashes, aligning with ATT&CK technique T1068 which covers Exploitation for Privilege Escalation.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable more sophisticated attacks. When the global bridge_list contains dangling references, any subsequent driver load operations that traverse this list can trigger memory corruption, leading to unpredictable behavior or system panics. The vulnerability is particularly relevant in embedded systems and devices where the meson drm driver is commonly used, such as single-board computers and media devices. The memory corruption can manifest as kernel oops, system crashes, or even allow for privilege escalation if exploited correctly. Additionally, the issue highlights poor resource management practices in kernel drivers, where proper cleanup routines are not implemented to ensure all allocated resources are properly released during module unloading, making it a prime candidate for exploitation by attackers targeting kernel-level vulnerabilities.
Mitigation strategies for CVE-2022-50256 require implementing proper resource cleanup procedures during driver unloading. The fix involves ensuring that drm bridges created by meson_encoder_hdmi_init and meson_encoder_cvbs_init are explicitly removed at aggregate driver unbind time using drm_bridge_remove before the module is unloaded. This ensures that all references to freed memory are properly cleaned from the global bridge_list, preventing the traversal of dangling pointers. System administrators should ensure that all kernel updates are applied promptly to address this vulnerability, as it represents a fundamental flaw in memory management that can be exploited to gain unauthorized access to system resources. Additionally, monitoring for KASAN reports and implementing proper driver load/unload sequences can help detect and prevent exploitation attempts. The vulnerability underscores the importance of adhering to kernel development best practices and implementing comprehensive resource management routines to prevent similar issues in other driver components.