f2fs: fix to avoid panic in do_recover_data()

As Jungyeon reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=203227

- 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

- Messages
 kernel BUG at fs/f2fs/recovery.c:549!
 RIP: 0010:recover_data+0x167a/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

During recovery, if ofs_of_node is inconsistent in between recovered
node page and original checkpointed node page, let's just fail recovery
instead of making kernel panic.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/recovery.c

@@ -551,7 +551,15 @@ retry_dn:
 		goto err;
 
 	f2fs_bug_on(sbi, ni.ino != ino_of_node(page));
-	f2fs_bug_on(sbi, ofs_of_node(dn.node_page) != ofs_of_node(page));
+
+	if (ofs_of_node(dn.node_page) != ofs_of_node(page)) {
+		f2fs_msg(sbi->sb, KERN_WARNING,
+			"Inconsistent ofs_of_node, ino:%lu, ofs:%u, %u",
+			inode->i_ino, ofs_of_node(dn.node_page),
+			ofs_of_node(page));
+		err = -EFAULT;
+		goto err;
+	}
 
 	for (; start < end; start++, dn.ofs_in_node++) {
 		block_t src, dest;