CVE-2023-53838

Vulnerability

Overview

The vulnerability is a race condition in the f2fs filesystem's handling of atomic write aborts. Atomic writes in f2fs provide transactional guarantees, allowing a series of writes to be committed atomically. When an atomic write operation is aborted, concurrent aborts could race, leaving the filesystem in an inconsistent state. The root cause is insufficient synchronization during abort processing, potentially corrupting metadata or user data.

Exploitation

Exploitation requires local access to the system and the ability to initiate atomic write operations (via the F2FS_IOC_START_ATOMIC_WRITE and F2FS_IOC_ABORT_ATOMIC_WRITE ioctls). An attacker would need to trigger concurrent aborts on the same atomic file inode, creating a race window. No special privileges beyond the ability to perform atomic writes are necessary, as these are available to unprivileged users if the filesystem is mounted with the appropriate options.

Impact

Successful exploitation could lead to filesystem corruption, data loss, or denial of service. The race may cause the Copy-on-Write (COW) inode to be improperly reclaimed or reused, resulting in dangling references or incorrect data being exposed. In worst-case scenarios, an attacker could corrupt files owned by other users or the system itself.

Mitigation

The issue is fixed in the Linux kernel by the commit referenced in the CVE. The fix synchronizes atomic write aborts using the inode lock and ensures the COW inode is reused only after all aborts complete. Users should update to a kernel version containing this patch. No workarounds are available; the vulnerability is resolved only by applying the kernel update.