CVE-2021-46938 is a vulnerability in the Linux kernel's device-mapper (dm) subsystem, specifically related to the handling of request-based mapped devices using blk_mq_tag_set structures. The flaw arises during the loading of a device-mapper table when the allocation or initialization of the blk_mq_tag_set fails. In this failure scenario, the pointer to blk_mq_tag_set is freed but not reset to NULL. Subsequently, when the device is removed, the cleanup function attempts to free the blk_mq_tag_set pointer again, resulting in a double-free condition. This double-free can lead to kernel memory corruption, which may cause a kernel panic or crash, as demonstrated by the kernel oops and panic logs included in the description. The vulnerability is rooted in improper error handling in the dm_mq_init_request_queue() function and insufficient pointer management in dm_mq_cleanup_mapped_device(). The fix involves setting the pointer to NULL after freeing it to prevent double-free attempts. This vulnerability affects Linux kernel versions containing the vulnerable device-mapper code prior to the fix, and it is relevant to systems using request-based device-mapper tables, which are common in multipath I/O configurations and other storage virtualization scenarios. Exploitation does not require user interaction but does require the ability to trigger device-mapper table loading and removal operations, which typically requires administrative privileges. No known exploits are reported in the wild at this time.

For European organizations, the impact of CVE-2021-46938 can be significant in environments relying on Linux servers with device-mapper configurations, especially those using multipath I/O for storage redundancy and performance. A successful exploitation can cause kernel crashes leading to denial of service (DoS), disrupting critical services and potentially causing data unavailability. In high-availability data centers, cloud infrastructure, and enterprise storage systems, such disruptions can result in operational downtime and financial losses. While the vulnerability does not directly enable privilege escalation or arbitrary code execution, the induced kernel panic can be leveraged in targeted attacks to cause service interruptions. Organizations in sectors such as finance, healthcare, telecommunications, and government, which often deploy Linux-based storage solutions, may face increased risk. Additionally, the complexity of the device-mapper subsystem means that recovery from crashes could require manual intervention, increasing incident response times.

To mitigate CVE-2021-46938, European organizations should: 1) Apply the latest Linux kernel patches that address this vulnerability as soon as they become available from their Linux distribution vendors. 2) Audit and monitor device-mapper configurations, particularly those using request-based mapped devices and multipath setups, to identify systems potentially affected. 3) Limit administrative access to systems that can load or remove device-mapper tables to trusted personnel only, reducing the risk of accidental or malicious triggering of the vulnerability. 4) Implement kernel crash monitoring and automated recovery mechanisms to minimize downtime in case of kernel panics. 5) Consider deploying kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) to reduce the impact of memory corruption vulnerabilities. 6) Maintain up-to-date backups and disaster recovery plans to ensure data integrity and availability in case of service disruption. 7) Engage in proactive vulnerability management and threat hunting to detect any anomalous activity related to device-mapper operations.