As Jungyeon reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=203229

- Overview
When mounting the attached crafted image, following errors are reported.
Additionally, it hangs on sync after trying to mount it.

The image is intentionally fuzzed from a normal f2fs image for testing.
Compile options for F2FS are as follows.
CONFIG_F2FS_FS=y
CONFIG_F2FS_STAT_FS=y
CONFIG_F2FS_FS_XATTR=y
CONFIG_F2FS_FS_POSIX_ACL=y
CONFIG_F2FS_CHECK_FS=y

- Reproduces
mkdir test
mount -t f2fs tmp.img test
sync

- Kernel message
 kernel BUG at fs/f2fs/recovery.c:591!
 RIP: 0010:recover_data+0x12d8/0x1780
 Call Trace:
  f2fs_recover_fsync_data+0x613/0x710
  f2fs_fill_super+0x1043/0x1aa0
  mount_bdev+0x16d/0x1a0
  mount_fs+0x4a/0x170
  vfs_kern_mount+0x5d/0x100
  do_mount+0x200/0xcf0
  ksys_mount+0x79/0xc0
  __x64_sys_mount+0x1c/0x20
  do_syscall_64+0x43/0xf0
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

With corrupted image wihch has out-of-range valid node/block count, during
recovery, once we failed due to no free space, it will trigger kernel
panic.

Adding sanity check on valid node/block count in f2fs_sanity_check_ckpt()
to detect such condition, so that potential panic can be avoided.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>