CVE-2024-49903

In the Linux kernel, the following vulnerability has been resolved:

jfs: Fix uaf in dbFreeBits

[syzbot reported]
==================================================================
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:587 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0xfe/0xd70 kernel/locking/mutex.c:752
Read of size 8 at addr ffff8880229254b0 by task syz-executor357/5216

CPU: 0 UID: 0 PID: 5216 Comm: syz-executor357 Not tainted 6.11.0-rc3-syzkaller-00156-gd7a5aa4b3c00 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:93 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
print_address_description mm/kasan/report.c:377 [inline]
print_report+0x169/0x550 mm/kasan/report.c:488
kasan_report+0x143/0x180 mm/kasan/report.c:601
__mutex_lock_common kernel/locking/mutex.c:587 [inline]
__mutex_lock+0xfe/0xd70 kernel/locking/mutex.c:752
dbFreeBits+0x7ea/0xd90 fs/jfs/jfs_dmap.c:2390
dbFreeDmap fs/jfs/jfs_dmap.c:2089 [inline]
dbFree+0x35b/0x680 fs/jfs/jfs_dmap.c:409
dbDiscardAG+0x8a9/0xa20 fs/jfs/jfs_dmap.c:1650
jfs_ioc_trim+0x433/0x670 fs/jfs/jfs_discard.c:100
jfs_ioctl+0x2d0/0x3e0 fs/jfs/ioctl.c:131
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83

Freed by task 5218:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579
poison_slab_object+0xe0/0x150 mm/kasan/common.c:240
__kasan_slab_free+0x37/0x60 mm/kasan/common.c:256
kasan_slab_free include/linux/kasan.h:184 [inline]
slab_free_hook mm/slub.c:2252 [inline]
slab_free mm/slub.c:4473 [inline]
kfree+0x149/0x360 mm/slub.c:4594
dbUnmount+0x11d/0x190 fs/jfs/jfs_dmap.c:278
jfs_mount_rw+0x4ac/0x6a0 fs/jfs/jfs_mount.c:247
jfs_remount+0x3d1/0x6b0 fs/jfs/super.c:454
reconfigure_super+0x445/0x880 fs/super.c:1083
vfs_cmd_reconfigure fs/fsopen.c:263 [inline]
vfs_fsconfig_locked fs/fsopen.c:292 [inline]
__do_sys_fsconfig fs/fsopen.c:473 [inline]
__se_sys_fsconfig+0xb6e/0xf80 fs/fsopen.c:345
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

[Analysis]
There are two paths (dbUnmount and jfs_ioc_trim) that generate race
condition when accessing bmap, which leads to the occurrence of uaf.

Use the lock s_umount to synchronize them, in order to avoid uaf caused
by race condition.