tresor: check hash of all read vba data

During one of the many re-factorization steps that were applied to the Tresor
library and its predecessor, the CBE library, one of the main features of the
project, the integrity check, accidentally received a grave regression. The
most recent version of the Tresor still used to check all hashes of meta-data
blocks but ignored the hashes of the actual data blocks.

With this commit, the hashes of all but yet uninitialized data blocks get
checked. The reason for ignoring uninitialized blocks is that they are not
actually read from disc but simply generated as an all-zeros block in the
driver in order to prevent having to initialize them all to zero in
Tresor-Init. That said, the integrity of these blocks cannot be compomised.
The according hashes in the meta data remain unset until the data block gets
written for the first time.

Ref #5062

repos/gems/src/lib/tresor/block_io.cc

@@ -104,6 +104,7 @@ void Block_io_channel::_read_client_data(bool &progress)
 	case REQ_SUBMITTED: _file.read(READ_OK, FILE_ERR, req._pba * BLOCK_SIZE, { (char *)&_blk, BLOCK_SIZE }, progress); break;
 	case READ_OK:
 
+		calc_hash(_blk, req._hash);
 		_generate_req<Crypto_request>(
 			PLAINTEXT_BLK_SUPPLIED, progress, Crypto_request::DECRYPT_CLIENT_DATA, req._client_req_offset,
 			req._client_req_tag, req._key_id, *(Key_value *)0, req._pba, req._vba, _blk);

repos/gems/src/lib/tresor/include/tresor/block_io.h

@@ -152,8 +152,8 @@ class Tresor::Block_io : public Module
 		struct Read_client_data : Request
 		{
 			Read_client_data(Module_id m, Module_channel_id c, Physical_block_address p, Virtual_block_address v,
-			                  Key_id k, Request_tag t, Request_offset o, bool &s)
+			                 Key_id k, Request_tag t, Request_offset o, Hash &h, bool &s)
-			: Request(m, c, Request::READ_CLIENT_DATA, o, t, k, p, v, *(Block*)0, *(Hash*)0, s) { }
+			: Request(m, c, Request::READ_CLIENT_DATA, o, t, k, p, v, *(Block*)0, h, s) { }
 		};
 
 		Block_io(Vfs::Env &, Xml_node const &);

repos/gems/src/lib/tresor/include/tresor/virtual_block_device.h

@@ -123,7 +123,7 @@ class Tresor::Virtual_block_device_channel : public Module_channel
 
 		void _read_vba(bool &);
 
-		bool _check_and_decode_read_blk(bool &, bool);
+		bool _check_and_decode_read_blk(bool &);
 
 		Tree_node_index _node_idx(Tree_level_index, Virtual_block_address) const;
 

repos/gems/src/lib/tresor/virtual_block_device.cc

@@ -90,7 +90,7 @@ void Virtual_block_device_channel::_read_vba(bool &progress)
 
 	case READ_BLK_SUCCEEDED:
 	{
-		if (!_check_and_decode_read_blk(progress, false))
+		if (!_check_and_decode_read_blk(progress))
 			break;
 
 		if (!_lvl) {
@@ -112,7 +112,7 @@ void Virtual_block_device_channel::_read_vba(bool &progress)
 			} else
 				_generate_req<Block_io::Read_client_data>(
 					READ_BLK_SUCCEEDED, progress, node.pba, _vba, req._curr_key_id,
-					req._client_req_tag, req._client_req_offset);
+					req._client_req_tag, req._client_req_offset, _hash);
 		_lvl--;
 		break;
 	}
@@ -147,13 +147,27 @@ void Virtual_block_device_channel::_update_nodes_of_branch_of_written_vba()
 }
 
 
-bool Virtual_block_device_channel::_check_and_decode_read_blk(bool &progress, bool check_leaf_data = true)
+bool Virtual_block_device_channel::_check_and_decode_read_blk(bool &progress)
 {
-	if (!check_leaf_data && !_lvl)
+	Request &req { *_req_ptr };
-		return true;
+	Hash *node_hash_ptr;
+	if (_lvl) {
+		calc_hash(_encoded_blk, _hash);
+		if (_lvl < snap().max_level)
+			node_hash_ptr = &_node(_lvl + 1, _vba).hash;
+		else
+			node_hash_ptr = &snap().hash;
+	} else {
+		Type_1_node &node { _node(_lvl + 1, _vba) };
+		if (req._type == Request::READ_VBA) {
+			if (node.gen == INITIAL_GENERATION)
+				return true;
+		} else
+			calc_hash(_data_blk, _hash);
 
-	Hash &hash { _lvl < snap().max_level ? _node(_lvl + 1, _vba).hash : snap().hash };
+		node_hash_ptr = &node.hash;
-	if (!check_hash(_lvl ? _encoded_blk : _data_blk, hash)) {
+	}
+	if (_hash != *node_hash_ptr) {
 		_mark_req_failed(progress, "check hash of read block");
 		return false;
 	}