CVE-2022-50628 in Linux
Summary
by MITRE • 12/08/2025
In the Linux kernel, the following vulnerability has been resolved:
drm/gud: Fix UBSAN warning
UBSAN complains about invalid value for bool:
[ 101.165172] [drm] Initialized gud 1.0.0 20200422 for 2-3.2:1.0 on minor 1
[ 101.213360] gud 2-3.2:1.0: [drm] fb1: guddrmfb frame buffer device
[ 101.213426] usbcore: registered new interface driver gud
[ 101.989431] ================================================================================
[ 101.989441] UBSAN: invalid-load in linux/include/linux/iosys-map.h:253:9
[ 101.989447] load of value 121 is not a valid value for type '_Bool'
[ 101.989451] CPU: 1 PID: 455 Comm: kworker/1:6 Not tainted 5.18.0-rc5-gud-5.18-rc5 #3
[ 101.989456] Hardware name: Hewlett-Packard HP EliteBook 820 G1/1991, BIOS L71 Ver. 01.44 04/12/2018
[ 101.989459] Workqueue: events_long gud_flush_work [gud]
[ 101.989471] Call Trace:
[ 101.989474] <TASK>
[ 101.989479] dump_stack_lvl+0x49/0x5f
[ 101.989488] dump_stack+0x10/0x12
[ 101.989493] ubsan_epilogue+0x9/0x3b
[ 101.989498] __ubsan_handle_load_invalid_value.cold+0x44/0x49
[ 101.989504] dma_buf_vmap.cold+0x38/0x3d
[ 101.989511] ? find_busiest_group+0x48/0x300
[ 101.989520] drm_gem_shmem_vmap+0x76/0x1b0 [drm_shmem_helper]
[ 101.989528] drm_gem_shmem_object_vmap+0x9/0xb [drm_shmem_helper]
[ 101.989535] drm_gem_vmap+0x26/0x60 [drm]
[ 101.989594] drm_gem_fb_vmap+0x47/0x150 [drm_kms_helper]
[ 101.989630] gud_prep_flush+0xc1/0x710 [gud]
[ 101.989639] ? _raw_spin_lock+0x17/0x40
[ 101.989648] gud_flush_work+0x1e0/0x430 [gud]
[ 101.989653] ? __switch_to+0x11d/0x470
[ 101.989664] process_one_work+0x21f/0x3f0
[ 101.989673] worker_thread+0x200/0x3e0
[ 101.989679] ? rescuer_thread+0x390/0x390
[ 101.989684] kthread+0xfd/0x130
[ 101.989690] ? kthread_complete_and_exit+0x20/0x20
[ 101.989696] ret_from_fork+0x22/0x30
[ 101.989706] </TASK>
[ 101.989708] ================================================================================
The source of this warning is in iosys_map_clear() called from dma_buf_vmap(). It conditionally sets values based on map->is_iomem. The iosys_map variables are allocated uninitialized on the stack leading to ->is_iomem having all kinds of values and not only 0/1.
Fix this by zeroing the iosys_map variables.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 02/22/2026
The vulnerability identified as CVE-2022-50628 represents a subtle but significant issue within the Linux kernel's graphics driver subsystem, specifically affecting the gud (Graphics USB Driver) module. This flaw manifests as a UBSAN (Undefined Behavior Sanitizer) warning that indicates an invalid value being loaded into a boolean type, which violates fundamental type safety principles. The issue occurs during the initialization and operation of graphics frame buffer devices, where the kernel attempts to map memory regions for graphics operations. The warning specifically points to a load operation in linux/include/linux/iosys-map.h at line 253, where a value of 121 is being interpreted as a boolean type, clearly violating the expected binary nature of boolean values. This type of error can indicate deeper memory management issues that may lead to unpredictable behavior in kernel space operations.
The technical root cause of this vulnerability stems from improper initialization of the iosys_map structure within the kernel's memory management system. When the iosys_map variables are allocated on the stack, they are not properly initialized, leaving them with arbitrary values that may include non-binary data. The conditional logic in the code depends on the is_iomem field of this structure to determine memory mapping behavior, but when this field contains values other than 0 or 1, it creates undefined behavior that UBSAN flags as problematic. This particular implementation pattern demonstrates a classic software engineering error where stack-allocated structures are not properly initialized before use, leading to potential security implications and system instability. The call trace reveals that this issue originates from the dma_buf_vmap function and propagates through several kernel subsystems including drm_gem_shmem_vmap, drm_gem_vmap, and ultimately reaches the gud_prep_flush function in the gud driver module.
The operational impact of this vulnerability extends beyond simple warning messages, as it represents a potential vector for more serious security issues within the kernel's memory management subsystem. While this particular instance may not directly lead to privilege escalation or arbitrary code execution, it indicates a broader pattern of uninitialized memory usage that could be exploited by attackers to create more severe vulnerabilities. The vulnerability affects systems running the Linux kernel version 5.18.0-rc5 and potentially other versions that include the gud driver module, particularly those that utilize USB graphics devices or graphics frame buffer operations. The presence of such issues in kernel space components raises concerns about overall system stability and security posture, as uninitialized memory can contain sensitive data or create unpredictable behavior that attackers might attempt to leverage.
The fix for CVE-2022-50628 involves a straightforward but critical change that addresses the root cause of the issue. By zeroing the iosys_map variables before use, the kernel ensures that all fields, particularly the is_iomem boolean field, contain predictable values of either 0 or 1. This approach aligns with established security practices and follows the principle of initializing all variables before use, which is a fundamental requirement in kernel development and a common recommendation in security standards such as those outlined in CWE-457. The solution demonstrates the importance of proper memory management in kernel space, where uninitialized memory can create security vulnerabilities that may not be immediately apparent but can have significant consequences. This fix also relates to ATT&CK technique T1068, which involves the exploitation of privileges and access control mechanisms, as improper memory handling in kernel space can create opportunities for privilege escalation. The remediation approach is consistent with industry best practices for kernel security and represents a standard defensive programming technique that should be applied broadly across kernel subsystems to prevent similar issues from arising in other components.
This vulnerability serves as an important reminder of the critical nature of memory initialization in kernel space development. The issue highlights how seemingly minor programming errors in kernel subsystems can create security concerns that affect the entire operating system. The fix demonstrates the importance of defensive programming practices, particularly in security-sensitive code areas where uninitialized memory can lead to unpredictable behavior. The UBSAN warning system plays a crucial role in identifying such issues during development and testing phases, helping to prevent vulnerabilities from reaching production systems. This case also illustrates the complexity of kernel security, where vulnerabilities may not manifest as obvious exploits but can create conditions that make more serious attacks possible. The resolution emphasizes the need for comprehensive testing and static analysis tools in kernel development to catch these subtle but potentially dangerous programming errors before they can be exploited in real-world scenarios.