f2fs: fix to do sanity check on ino and xnid
In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to do sanity check on ino and xnid

syzbot reported a f2fs bug as below:

INFO: task syz-executor140:5308 blocked for more than 143 seconds.
      Not tainted 6.14.0-rc7-syzkaller-00069-g81e4f8d68c66 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor140 state:D stack:24016 pid:5308  tgid:5308  ppid:5306   task_flags:0x400140 flags:0x00000006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5378 [inline]
 __schedule+0x190e/0x4c90 kernel/sched/core.c:6765
 __schedule_loop kernel/sched/core.c:6842 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6857
 io_schedule+0x8d/0x110 kernel/sched/core.c:7690
 folio_wait_bit_common+0x839/0xee0 mm/filemap.c:1317
 __folio_lock mm/filemap.c:1664 [inline]
 folio_lock include/linux/pagemap.h:1163 [inline]
 __filemap_get_folio+0x147/0xb40 mm/filemap.c:1917
 pagecache_get_page+0x2c/0x130 mm/folio-compat.c:87
 find_get_page_flags include/linux/pagemap.h:842 [inline]
 f2fs_grab_cache_page+0x2b/0x320 fs/f2fs/f2fs.h:2776
 __get_node_page+0x131/0x11b0 fs/f2fs/node.c:1463
 read_xattr_block+0xfb/0x190 fs/f2fs/xattr.c:306
 lookup_all_xattrs fs/f2fs/xattr.c:355 [inline]
 f2fs_getxattr+0x676/0xf70 fs/f2fs/xattr.c:533
 __f2fs_get_acl+0x52/0x870 fs/f2fs/acl.c:179
 f2fs_acl_create fs/f2fs/acl.c:375 [inline]
 f2fs_init_acl+0xd7/0x9b0 fs/f2fs/acl.c:418
 f2fs_init_inode_metadata+0xa0f/0x1050 fs/f2fs/dir.c:539
 f2fs_add_inline_entry+0x448/0x860 fs/f2fs/inline.c:666
 f2fs_add_dentry+0xba/0x1e0 fs/f2fs/dir.c:765
 f2fs_do_add_link+0x28c/0x3a0 fs/f2fs/dir.c:808
 f2fs_add_link fs/f2fs/f2fs.h:3616 [inline]
 f2fs_mknod+0x2e8/0x5b0 fs/f2fs/namei.c:766
 vfs_mknod+0x36d/0x3b0 fs/namei.c:4191
 unix_bind_bsd net/unix/af_unix.c:1286 [inline]
 unix_bind+0x563/0xe30 net/unix/af_unix.c:1379
 __sys_bind_socket net/socket.c:1817 [inline]
 __sys_bind+0x1e4/0x290 net/socket.c:1848
 __do_sys_bind net/socket.c:1853 [inline]
 __se_sys_bind net/socket.c:1851 [inline]
 __x64_sys_bind+0x7a/0x90 net/socket.c:1851
 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

Let's dump and check metadata of corrupted inode, it shows its xattr_nid
is the same to its i_ino.

dump.f2fs -i 3 chaseyu.img.raw
i_xattr_nid                             [0x       3 : 3]

So that, during mknod in the corrupted directory, it tries to get and
lock inode page twice, result in deadlock.

- f2fs_mknod
 - f2fs_add_inline_entry
  - f2fs_get_inode_page --- lock dir's inode page
   - f2fs_init_acl
    - f2fs_acl_create(dir,..)
     - __f2fs_get_acl
      - f2fs_getxattr
       - lookup_all_xattrs
        - __get_node_page --- try to lock dir's inode page

In order to fix this, let's add sanity check on ino and xnid.