ext4: fix use-after-free in ext4_rename_dir_prepare

ext4: fix use-after-free in ext4_rename_dir_prepare

We got issue as follows:
EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
ext4_get_first_dir_block: bh->b_data=0xffff88810bee6000 len=34478
ext4_get_first_dir_block: *parent_de=0xffff88810beee6ae bh->b_data=0xffff88810bee6000
ext4_rename_dir_prepare: [1] parent_de=0xffff88810beee6ae
==================================================================
BUG: KASAN: use-after-free in ext4_rename_dir_prepare+0x152/0x220
Read of size 4 at addr ffff88810beee6ae by task rep/1895

CPU: 13 PID: 1895 Comm: rep Not tainted 5.10.0+ #241
Call Trace:
 dump_stack+0xbe/0xf9
 print_address_description.constprop.0+0x1e/0x220
 kasan_report.cold+0x37/0x7f
 ext4_rename_dir_prepare+0x152/0x220
 ext4_rename+0xf44/0x1ad0
 ext4_rename2+0x11c/0x170
 vfs_rename+0xa84/0x1440
 do_renameat2+0x683/0x8f0
 __x64_sys_renameat+0x53/0x60
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f45a6fc41c9
RSP: 002b:00007ffc5a470218 EFLAGS: 00000246 ORIG_RAX: 0000000000000108
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f45a6fc41c9
RDX: 0000000000000005 RSI: 0000000020000180 RDI: 0000000000000005
RBP: 00007ffc5a470240 R08: 00007ffc5a470160 R09: 0000000020000080
R10: 00000000200001c0 R11: 0000000000000246 R12: 0000000000400bb0
R13: 00007ffc5a470320 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:00000000440015ce refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x10beee
flags: 0x200000000000000()
raw: 0200000000000000 ffffea00043ff4c8 ffffea0004325608 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88810beee580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88810beee600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88810beee680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                  ^
 ffff88810beee700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88810beee780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
Disabling lock debugging due to kernel taint
ext4_rename_dir_prepare: [2] parent_de->inode=3537895424
ext4_rename_dir_prepare: [3] dir=0xffff888124170140
ext4_rename_dir_prepare: [4] ino=2
ext4_rename_dir_prepare: ent->dir->i_ino=2 parent=-757071872

Reason is first directory entry which 'rec_len' is 34478, then will get illegal
parent entry. Now, we do not check directory entry after read directory block
in 'ext4_get_first_dir_block'.
To solve this issue, check directory entry in 'ext4_get_first_dir_block'.

[ Trigger an ext4_error() instead of just warning if the directory is
  missing a '.' or '..' entry.   Also make sure we return an error code
  if the file system is corrupted.  -TYT ]

Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220414025223.4113128-1-yebin10@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org