f2fs: use global inline_xattr_slab instead of per-sb slab cache

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

f2fs: use global inline_xattr_slab instead of per-sb slab cache

As Hong Yun reported in mailing list:

loop7: detected capacity change from 0 to 131072

------------[ cut here ]------------

kmem_cache of name 'f2fs_xattr_entry-7:7' already exists

WARNING: CPU: 0 PID: 24426 at mm/slab_common.c:110 kmem_cache_sanity_check mm/slab_common.c:109 [inline]

WARNING: CPU: 0 PID: 24426 at mm/slab_common.c:110 __kmem_cache_create_args+0xa6/0x320 mm/slab_common.c:307

CPU: 0 UID: 0 PID: 24426 Comm: syz.7.1370 Not tainted 6.17.0-rc4 #1 PREEMPT(full)

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014

RIP: 0010:kmem_cache_sanity_check mm/slab_common.c:109 [inline]

RIP: 0010:__kmem_cache_create_args+0xa6/0x320 mm/slab_common.c:307

Call Trace:

__kmem_cache_create include/linux/slab.h:353 [inline]

f2fs_kmem_cache_create fs/f2fs/f2fs.h:2943 [inline]

f2fs_init_xattr_caches+0xa5/0xe0 fs/f2fs/xattr.c:843

f2fs_fill_super+0x1645/0x2620 fs/f2fs/super.c:4918

get_tree_bdev_flags+0x1fb/0x260 fs/super.c:1692

vfs_get_tree+0x43/0x140 fs/super.c:1815

do_new_mount+0x201/0x550 fs/namespace.c:3808

do_mount fs/namespace.c:4136 [inline]

__do_sys_mount fs/namespace.c:4347 [inline]

__se_sys_mount+0x298/0x2f0 fs/namespace.c:4324

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0x8e/0x3a0 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x76/0x7e

The bug can be reproduced w/ below scripts:

- mount /dev/vdb /mnt1

- mount /dev/vdc /mnt2

- umount /mnt1

- mounnt /dev/vdb /mnt1

The reason is if we created two slab caches, named f2fs_xattr_entry-7:3

and f2fs_xattr_entry-7:7, and they have the same slab size. Actually,

slab system will only create one slab cache core structure which has

slab name of "f2fs_xattr_entry-7:3", and two slab caches share the same

structure and cache address.

So, if we destroy f2fs_xattr_entry-7:3 cache w/ cache address, it will

decrease reference count of slab cache, rather than release slab cache

entirely, since there is one more user has referenced the cache.

Then, if we try to create slab cache w/ name "f2fs_xattr_entry-7:3" again,

slab system will find that there is existed cache which has the same name

and trigger the warning.

Let's changes to use global inline_xattr_slab instead of per-sb slab cache

for fixing.