CVE-2021-47335: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47335 is a vulnerability in the Linux kernel's F2FS (Flash-Friendly File System) that involves a use-after-free issue during filesystem recovery. The vulnerability was discovered and reported by syzbot, and was resolved in May 2021. The issue affects the F2FS filesystem implementation when multiple filesystem instances are present (NVD).

The vulnerability occurs when multiple F2FS filesystem instances race on accessing the global fsync_entry_slab pointer, resulting in a use-after-free issue of the slab cache. The issue manifests during F2FS recovery operations, specifically in the kmem_cache_destroy function at mm/slab_common.c:486. The bug is triggered through the call chain: f2fs_recover_fsync_data -> f2fs_fill_super -> mount_bdev -> legacy_get_tree -> vfs_get_tree -> do_new_mount (Kernel Commit).

The vulnerability could lead to use-after-free conditions in the kernel, potentially resulting in system crashes, memory corruption, or privilege escalation. The issue affects systems using the F2FS filesystem with multiple filesystem instances (NVD).

The vulnerability requires local access to a system using F2FS filesystem and the ability to mount multiple F2FS filesystem instances. No public exploits have been reported in the wild (NVD).

The issue has been fixed by modifying the initialization and destruction of the slab cache to occur only once during module init/destroy procedure. The fix involves changes to multiple F2FS-related files including f2fs.h, recovery.c, and super.c. Users should update their Linux kernel to a version containing the fix (Kernel Commit).