Merge bitcoin/bitcoin#28052: blockstorage: XOR blocksdir *.dat files

fa895c7283 mingw: Document mode wbx workaround (MarcoFalke)
fa359255fe Add -blocksxor boolean option (MarcoFalke)
fa7f7ac040 Return XOR AutoFile from BlockManager::Open*File() (MarcoFalke)

Pull request description:

  Currently the *.dat files in the blocksdir store the data received from remote peers as-is. This may be problematic when a program other than Bitcoin Core tries to interpret them by accident. For example, an anti-virus program or other program may scan them and move them into quarantine, or delete them, or corrupt them. This may cause Bitcoin Core to fail a reorg, or fail to reply to block requests (via P2P, RPC, REST, ...).

  Fix this, similar to https://github.com/bitcoin/bitcoin/pull/6650, by rolling a random XOR pattern over the dat files when writing or reading them.

  Obviously this can only protect against programs that accidentally and unintentionally are trying to mess with the dat files. Any program that intentionally wants to mess with the dat files can still trivially do so.

  The XOR pattern is only applied when the blocksdir is freshly created, and there is an option to disable it (on creation), so that people can disable it, if needed.

ACKs for top commit:
  achow101:
    ACK fa895c7283
  TheCharlatan:
    Re-ACK fa895c7283
  hodlinator:
    ACK fa895c7283

Tree-SHA512: c92a6a717da83bc33a9b8671a779eeefde2c63b192362ba1d71e6535ee31d08e2802b74acc908345197de9daac6930e4771595ee25b09acd5a67f7ea34854720

doc/files.md

@@ -47,8 +47,9 @@ Subdirectory       | File(s)               | Description
 -------------------|-----------------------|------------
 `blocks/`          |                       | Blocks directory; can be specified by `-blocksdir` option (except for `blocks/index/`)
 `blocks/index/`    | LevelDB database      | Block index; `-blocksdir` option does not affect this path
-`blocks/`          | `blkNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Actual Bitcoin blocks (in network format, dumped in raw on disk, 128 MiB per file)
+`blocks/`          | `blkNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Actual Bitcoin blocks (dumped in network format, 128 MiB per file)
 `blocks/`          | `revNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Block undo data (custom format)
+`blocks/`          | `xor.dat`             | Rolling XOR pattern for block and undo data files
 `chainstate/`      | LevelDB database      | Blockchain state (a compact representation of all currently unspent transaction outputs (UTXOs) and metadata about the transactions they are from)
 `indexes/txindex/` | LevelDB database      | Transaction index; *optional*, used if `-txindex=1`
 `indexes/blockfilter/basic/db/` | LevelDB database      | Blockfilter index LevelDB database for the basic filtertype; *optional*, used if `-blockfilterindex=basic`

doc/release-notes-28052.md

@@ -0,0 +1,6 @@
+Blockstorage
+============
+
+Block files are now XOR'd by default with a key stored in the blocksdir.
+Previous releases of Bitcoin Core or previous external software will not be able to read the blocksdir with a non-zero XOR-key.
+Refer to the `-blocksxor` help for more details.