CVE-2022-50550 in Linux
Summary
by MITRE • 10/07/2025
In the Linux kernel, the following vulnerability has been resolved:
blk-iolatency: Fix memory leak on add_disk() failures
When a gendisk is successfully initialized but add_disk() fails such as when a loop device has invalid number of minor device numbers specified, blkcg_init_disk() is called during init and then blkcg_exit_disk() during error handling. Unfortunately, iolatency gets initialized in the former but doesn't get cleaned up in the latter.
This is because, in non-error cases, the cleanup is performed by del_gendisk() calling rq_qos_exit(), the assumption being that rq_qos policies, iolatency being one of them, can only be activated once the disk is fully registered and visible. That assumption is true for wbt and iocost, but not so for iolatency as it gets initialized before add_disk() is called.
It is desirable to lazy-init rq_qos policies because they are optional features and add to hot path overhead once initialized - each IO has to walk all the registered rq_qos policies. So, we want to switch iolatency to lazy init too. However, that's a bigger change. As a fix for the immediate problem, let's just add an extra call to rq_qos_exit() in blkcg_exit_disk(). This is safe because duplicate calls to rq_qos_exit() become noop's.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-2022-50550 represents a memory leak within the Linux kernel's block I/O subsystem, specifically affecting the iolatency tracking mechanism. This issue occurs during the initialization process of generic disk devices where the kernel attempts to register a gendisk structure but encounters a failure during the add_disk() operation. The problem manifests when a loop device is configured with an invalid number of minor device numbers, causing the initialization sequence to fail before the disk can be properly registered. The kernel's block layer employs a complex initialization and cleanup mechanism involving multiple components including blkcg_init_disk() and blkcg_exit_disk() functions that handle the setup and teardown of various I/O quality of service policies.
The technical flaw stems from an inconsistent cleanup approach between different I/O quality of service policies within the kernel's request queue subsystem. While the kernel correctly handles cleanup for wbt (writeback throttling) and iocost policies through the standard del_gendisk() path that calls rq_qos_exit(), the iolatency policy does not follow this same pattern. This occurs because iolatency initialization happens before add_disk() is called, unlike other policies that are initialized only after successful disk registration. When the add_disk() operation fails, blkcg_exit_disk() is invoked to handle error cleanup, but it does not properly clean up the iolatency policy initialization that occurred during blkcg_init_disk(). This creates a memory leak where iolatency tracking structures remain allocated in memory even though the disk operation ultimately fails.
The operational impact of this vulnerability extends beyond simple memory consumption, potentially leading to system instability and resource exhaustion over time. The memory leak affects systems that frequently attempt to create or configure loop devices with invalid parameters, which can occur during automated provisioning, testing, or misconfiguration scenarios. As the kernel's block layer handles thousands of I/O operations per second, even small memory leaks can compound over time, eventually consuming significant portions of available system memory. This vulnerability affects the broader Linux kernel ecosystem and impacts any system running kernel versions that contain this specific code path, particularly those utilizing loop devices or block I/O quality of service mechanisms. The issue is classified as a memory leak under CWE-401 and represents a failure in resource management within the kernel's I/O subsystem.
The fix implemented addresses this specific memory leak by adding an additional call to rq_qos_exit() within the blkcg_exit_disk() function, ensuring that iolatency policy cleanup occurs regardless of whether the add_disk() operation succeeds or fails. This approach maintains backward compatibility while resolving the immediate memory leak issue without requiring extensive changes to the existing initialization framework. The solution leverages the fact that duplicate calls to rq_qos_exit() are safe and become no-ops, preventing any potential side effects from the additional cleanup call. This remediation aligns with the principle of least privilege and proper resource management, ensuring that all allocated resources are properly freed during error conditions. The fix also aligns with ATT&CK technique T1490, which covers resource exhaustion attacks, by preventing the gradual depletion of system memory through improper resource cleanup. The approach demonstrates a careful balance between maintaining system stability and implementing targeted fixes to address specific memory management issues within the kernel's complex I/O handling architecture.