CVE-2022-49821 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
mISDN: fix possible memory leak in mISDN_dsp_element_register()
Afer commit 1fa5ae857bb1 ("driver core: get rid of struct device's bus_id string array"), the name of device is allocated dynamically, use put_device() to give up the reference, so that the name can be freed in kobject_cleanup() when the refcount is 0.
The 'entry' is going to be freed in mISDN_dsp_dev_release(), so the kfree() is removed. list_del() is called in mISDN_dsp_dev_release(), so it need be initialized.
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Analysis
by VulDB Data Team • 11/10/2025
The vulnerability CVE-2022-49821 addresses a memory leak in the Linux kernel's mISDN subsystem, specifically within the mISDN_dsp_element_register() function. This issue emerged following a significant kernel refactoring commit 1fa5ae857bb1 that eliminated the static bus_id string array from the struct device structure. The refactoring introduced dynamic allocation of device names and required the use of put_device() to properly manage reference counts, enabling automatic cleanup of device names through kobject_cleanup() when reference counts reached zero. The mISDN subsystem, which provides support for ISDN (Integrated Services Digital Network) device drivers, was affected by improper memory management during device registration operations.
The technical flaw stems from improper handling of device entry structures within the mISDN DSP (Digital Signal Processing) subsystem. When device entries were registered, the code attempted to free memory that was already scheduled for cleanup during the device release process. The original implementation contained a kfree() call that was unnecessary and potentially problematic since the 'entry' structure was already destined for freeing in the mISDN_dsp_dev_release() function. Additionally, the code failed to properly initialize list structures before calling list_del() operations, which could lead to undefined behavior when attempting to remove elements from linked lists.
The operational impact of this vulnerability manifests as a memory leak that accumulates over time, particularly in systems running ISDN applications or devices that frequently register and unregister mISDN DSP elements. While the leak may appear small per individual operation, repeated registration cycles can lead to significant memory consumption that affects overall system performance and stability. The vulnerability is particularly concerning in embedded systems or servers where memory resources are constrained and continuous operation is expected. Attackers could potentially exploit this memory leak to cause denial of service conditions through memory exhaustion, though direct exploitation for privilege escalation or code execution appears unlikely based on the nature of the flaw.
Mitigation strategies should focus on applying the kernel patch that resolves the memory management issue by removing the redundant kfree() call and ensuring proper initialization of list structures before list operations. System administrators should prioritize updating to kernel versions containing the fix, particularly in production environments running ISDN applications. Monitoring for memory usage patterns in systems utilizing mISDN drivers can help detect potential exploitation attempts or accumulation of leaked memory. The vulnerability aligns with CWE-401, which addresses improper management of memory allocation and deallocation, and may be relevant to ATT&CK techniques related to resource exhaustion and system stability compromise. Organizations should also implement regular kernel update policies and maintain awareness of similar memory management issues in other kernel subsystems that may exhibit similar patterns of improper resource cleanup.