CVE-2021-47595: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47595 affects the Linux kernel's Enhanced Transmission Selection (ETS) scheduler implementation. The vulnerability was discovered when a specific sequence of traffic control (tc) commands caused a kernel crash. The issue was reported by Shuang Li and affects Linux kernel versions from 5.10.83 up to (excluding) 5.10.88 and from 5.15.6 up to (excluding) 5.15.11 (NVD).

The vulnerability occurs in the ETS scheduler's queue management system when removing classes from the round-robin list. The bug manifests when attempting to remove 'q->classes[i].alist' without properly checking if the DRR class was part of the active list. In the ETS scheduler, DRR classes should only belong to that list if the queue length is greater than zero. The issue leads to a listdel corruption where the next pointer contains LISTPOISON1 (dead000000000100), ultimately resulting in a kernel panic (Kernel Patch).

When exploited, this vulnerability causes a kernel panic, leading to a system crash. The issue has a CVSS v3.1 Base Score of 5.5 MEDIUM (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H), indicating that while it requires local access and low privileges, it can cause a complete denial of service through system crashes (NVD).

The issue has been fixed by adding a check for non-zero queue length before removing classes from the list. The fix involves testing for 'q->classes[i].qdisc->q.qlen' before removing from the list. Users should upgrade to Linux kernel versions 5.10.88, 5.15.11, or later to receive the fix (Kernel Patch).