In ethereum, as a node controller I can able to access the leveldb. If I try to modify some value directly into the db, the value of the new hash and the next block's parent hash doesn't match right ?. How the current version of ethereum handle this problem? . Does it need to went over each and every block to check the data integrity ??
If you modify data, it will not reflect on other nodes. If newer nodes sync from node with corrupt data, those nodes will reject such blocks.
For nodes you control, you (as a malicious user)
- Can manipulate data
- Can manipulate node software to prevent integrity checks
But you do not have any control over other nodes in network.