CVE-2023-54127: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54127 is a double-free vulnerability in the Linux kernel's JFS (Journaled File System) subsystem, specifically in the dbUnmount() function triggered after a failed jfs_remount() operation. The flaw was discovered via Syzkaller fuzzing and publicly disclosed on December 24, 2025. It affects the Linux kernel across multiple stable branches, with patches available for affected versions. The vulnerability carries a CVSS v3.1 base score of 5.5 (Medium), reflecting a local attack vector with high availability impact (Red Hat CVE, Red Hat Bugzilla).

The root cause is a double-free memory error (CWE-415) in fs/jfs/jfs_dmap.c. When jfs_remount() fails — specifically if either diMount() or dbMount() fail during the remount process — the cleanup path calls diUnmount() or dbUnmount(), which frees the block map (bmap) structure. However, JFS_SBI(ipbmap->i_sb)->bmap is not set to NULL after the kfree() in dbUnmount(), leaving a dangling pointer. On the subsequent unmount or remount attempt, dbUnmount() is called again on the already-freed memory, triggering a KASAN-detected double-free. Exploitation requires local access and the ability to perform mount/remount operations on a JFS filesystem (Red Hat Bugzilla).

Successful exploitation can cause kernel memory corruption and system crashes, resulting in a denial of service (kernel panic). The vulnerability has no confidentiality or integrity impact, but the high availability impact means a low-privileged local attacker could destabilize or crash the affected system. There is no evidence of lateral movement potential or data exposure risk associated with this vulnerability (Red Hat CVE, Red Hat Bugzilla).

The primary remediation is to update to a patched Linux kernel version that includes the fix for fs/jfs/jfs_dmap.c (setting bmap to NULL after kfree() in dbUnmount()). Patches have been committed to multiple stable kernel branches (commits 2f7a364, 6f8b344, 798c5f6, aa5b019). As a workaround, administrators can restrict local user access to mount and remount operations, or avoid using JFS filesystems where possible. Monitoring system logs for unusual filesystem mount/remount activity is also recommended (Red Hat Bugzilla, Red Hat CVE).