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

jfs: Fix uaf in dbFreeBits

[syzbot reported]

BUG: KASAN: slab-use-after-free in __mutexlockcommon kernel/locking/mutex.c:587 [inline] BUG: KASAN: slab-use-after-free in _mutexlock+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> __dumpstack lib/dumpstack.c:93 [inline] dump_stacklvl+0x241/0x360 lib/dumpstack.c:119 printaddressdescription mm/kasan/report.c:377 [inline] printreport+0x169/0x550 mm/kasan/report.c:488 kasanreport+0x143/0x180 mm/kasan/report.c:601 __mutexlockcommon kernel/locking/mutex.c:587 [inline] __mutexlock+0xfe/0xd70 kernel/locking/mutex.c:752 dbFreeBits+0x7ea/0xd90 fs/jfs/jfsdmap.c:2390 dbFreeDmap fs/jfs/jfsdmap.c:2089 [inline] dbFree+0x35b/0x680 fs/jfs/jfsdmap.c:409 dbDiscardAG+0x8a9/0xa20 fs/jfs/jfsdmap.c:1650 jfsioctrim+0x433/0x670 fs/jfs/jfsdiscard.c:100 jfsioctl+0x2d0/0x3e0 fs/jfs/ioctl.c:131 vfsioctl fs/ioctl.c:51 [inline] __dosysioctl fs/ioctl.c:907 [inline] __sesysioctl+0xfc/0x170 fs/ioctl.c:893 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xf3/0x230 arch/x86/entry/common.c:83

Freed by task 5218: kasansavestack mm/kasan/common.c:47 [inline] kasansavetrack+0x3f/0x80 mm/kasan/common.c:68 kasansavefreeinfo+0x40/0x50 mm/kasan/generic.c:579 poisonslab_object+0xe0/0x150 mm/kasan/common.c:240 __kasanslabfree+0x37/0x60 mm/kasan/common.c:256 kasanslabfree include/linux/kasan.h:184 [inline] slabfreehook mm/slub.c:2252 [inline] slabfree mm/slub.c:4473 [inline] kfree+0x149/0x360 mm/slub.c:4594 dbUnmount+0x11d/0x190 fs/jfs/jfsdmap.c:278 jfsmountrw+0x4ac/0x6a0 fs/jfs/jfsmount.c:247 jfsremount+0x3d1/0x6b0 fs/jfs/super.c:454 reconfiguresuper+0x445/0x880 fs/super.c:1083 vfscmdreconfigure fs/fsopen.c:263 [inline] vfsfsconfig_locked fs/fsopen.c:292 [inline] __dosysfsconfig fs/fsopen.c:473 [inline] __sesysfsconfig+0xb6e/0xf80 fs/fsopen.c:345 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xf3/0x230 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x77/0x7f

[Analysis] There are two paths (dbUnmount and jfsioctrim) 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.