CVE-2021-46956: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-46956 is a memory leak vulnerability in the Linux kernel's virtiofs filesystem component, specifically in the virtio_fs_probe() function. The vulnerability was discovered when passing the same tag twice to QEMU, which resulted in a memory leak in the virtiofs module. This issue affects Linux kernel versions from 5.4 up to (excluding) 5.4.118, from 5.5 up to (excluding) 5.10.36, from 5.11 up to (excluding) 5.11.20, and from 5.12 up to (excluding) 5.12.3 (NVD).

The vulnerability occurs in the virtio_fs_probe() function where memory allocated for fs->vqs is not properly freed when the probe operation fails. The issue manifests when the same tag is passed twice to QEMU, resulting in a probe failure with error -17. The memory leak was confirmed through kmemleak, which reported an unreferenced object of size 1024 bytes in the systemd-udevd process. The CVSS v3.1 base score is 5.5 (MEDIUM) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability results in a memory leak in the Linux kernel's virtiofs filesystem component. While the immediate impact is resource consumption through memory leaks, the vulnerability does not allow for information disclosure or system compromise. The issue primarily affects system stability and resource availability (NVD).

The vulnerability requires local access and low privileges to exploit. The attack complexity is low, but no user interaction is needed. There are no known exploits in the wild. The vulnerability is triggered specifically when passing duplicate tags to QEMU in a virtiofs configuration (NVD).

The vulnerability has been patched by adding a proper cleanup call (kfree(fs->vqs)) in the error handling path of virtio_fs_probe(). The fix was committed upstream and backported to affected stable kernel versions. Users should update their Linux kernel to versions 5.4.118, 5.10.36, 5.11.20, 5.12.3 or later to address this vulnerability (Kernel Patch).