CVE-2023-53616: jfs: fix invalid free of JFS_IP(ipimap)->i_imap in diUnmount
In the Linux kernel, the following vulnerability has been resolved:
jfs: fix invalid free of JFS_IP(ipimap)->i_imap in diUnmount
syzbot found an invalid-free in diUnmount:
BUG: KASAN: double-free in slab_free mm/slub.c:3661 [inline]
BUG: KASAN: double-free in __kmem_cache_free+0x71/0x110 mm/slub.c:3674
Free of addr ffff88806f410000 by task syz-executor131/3632
CPU: 0 PID: 3632 Comm: syz-executor131 Not tainted 6.1.0-rc7-syzkaller-00012-gca57f02295f1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
print_address_description+0x74/0x340 mm/kasan/report.c:284
print_report+0x107/0x1f0 mm/kasan/report.c:395
kasan_report_invalid_free+0xac/0xd0 mm/kasan/report.c:460
____kasan_slab_free+0xfb/0x120
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1724 [inline]
slab_free_freelist_hook+0x12e/0x1a0 mm/slub.c:1750
slab_free mm/slub.c:3661 [inline]
__kmem_cache_free+0x71/0x110 mm/slub.c:3674
diUnmount+0xef/0x100 fs/jfs/jfs_imap.c:195
jfs_umount+0x108/0x370 fs/jfs/jfs_umount.c:63
jfs_put_super+0x86/0x190 fs/jfs/super.c:194
generic_shutdown_super+0x130/0x310 fs/super.c:492
kill_block_super+0x79/0xd0 fs/super.c:1428
deactivate_locked_super+0xa7/0xf0 fs/super.c:332
cleanup_mnt+0x494/0x520 fs/namespace.c:1186
task_work_run+0x243/0x300 kernel/task_work.c:179
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0x664/0x2070 kernel/exit.c:820
do_group_exit+0x1fd/0x2b0 kernel/exit.c:950
__do_sys_exit_group kernel/exit.c:961 [inline]
__se_sys_exit_group kernel/exit.c:959 [inline]
__x64_sys_exit_group+0x3b/0x40 kernel/exit.c:959
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
[...]
JFS_IP(ipimap)->i_imap is not setting to NULL after free in diUnmount.
If jfs_remount() free JFS_IP(ipimap)->i_imap but then failed at diMount().
JFS_IP(ipimap)->i_imap will be freed once again.
Fix this problem by setting JFS_IP(ipimap)->i_imap to NULL after free.
Security readout for executives and security teams
Plain-English summary
This is a Linux kernel bug in the JFS filesystem unmount/remount path. Under a failed remount sequence, the kernel could try to free the same JFS internal allocation twice. The public record does not provide CVSS, impact rating, or evidence of exploitation.
Executive priority
Treat this as a kernel maintenance item unless your environment uses JFS. There is no source-provided severity score or exploitation evidence, but kernel memory-management bugs deserve timely patching on systems with relevant filesystem exposure.
Technical view
The issue is an invalid free in JFS diUnmount: JFS_IP(ipimap)->i_imap was freed but not set to NULL. If jfs_remount() freed it and diMount() later failed, diUnmount() could free it again. The kernel fix sets the pointer to NULL after freeing.
Likely exposure
Exposure appears limited to Linux systems with JFS support where JFS filesystems are mounted or remounted. The source bundle lists Linux kernel versions as affected but does not provide distribution package mappings or runtime exploit prerequisites.
Exploitation context
The evidence comes from a syzbot KASAN double-free report. The source bundle marks KEV as false and includes no cited report of active exploitation, public exploit use, or weaponized attack path.
Researcher notes
The record is specific to fs/jfs/jfs_imap.c diUnmount behavior. The main uncertainty is exploitability: the public bundle shows a double-free found by fuzzing, not a demonstrated privilege escalation, denial of service, or remote attack path.
Mitigation direction
Update to a vendor-supported kernel containing the referenced stable JFS fixes.
Check distribution advisories for the exact fixed kernel package in your environment.
Prioritize systems that actively mount or remount JFS filesystems.
If JFS is unused, evaluate disabling JFS support through normal OS hardening procedures.
Validation and detection
Inventory Linux hosts and identify kernels with JFS support enabled.
Check whether any systems mount JFS filesystems in production or test.
Compare installed kernel builds against vendor advisories and stable fix references.
Review kernel logs for JFS mount, remount, or unmount failures.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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Oct 4, 2025, 15:44 UTC (UTC+00:00)
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