CVE-2021-47342: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47342 affects the Linux kernel's ext4 filesystem implementation. The vulnerability was discovered in relation to a possible Use-After-Free (UAF) condition when remounting a Multiple Mount Protection (MMP) protected filesystem as read-only. This issue emerged after the implementation of commit 618f003199c6 which was intended to fix a memory leak in ext4_fill_super. The vulnerability was reported by Ye Bin and disclosed in 2024 (NVD).

The vulnerability occurs due to a race condition where the kmmpd thread can exit while the filesystem is being remounted as read-only, causing sbi->s_mmp_tsk to point at freed memory. This can be triggered when ext4_stop_mmpd() attempts to access this memory. The issue has been assigned a CVSS v3.1 base score of 7.8 (HIGH) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NVD).

The vulnerability could lead to a Use-After-Free condition in the Linux kernel, potentially resulting in system crashes, information leaks, or privilege escalation. The issue affects Linux kernel versions up to (excluding) 5.10.77 and versions from (including) 5.11 up to (excluding) 5.13.3 (NVD).

The vulnerability requires local access and low privileges to exploit. An attacker would need to have the ability to mount and remount filesystems on the affected system. The attack complexity is considered low, but requires specific timing to trigger the race condition (NVD).

The vulnerability has been fixed by modifying the kmmpd() function to only allow exit when explicitly stopped via ext4_stop_mmpd(). The fix has been implemented in Linux kernel versions 5.10.77 and 5.13.3 and later. Users should upgrade to these or later versions to mitigate the vulnerability (Kernel Patch).