[HDFS-14706] Checksums are not checked if block meta file is less than 7 bytes

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.3.0
• Fix Version/s: 3.3.0, 3.2.1, 3.1.3
• Target Version/s: 3.3.0
• Assignee: Stephen O'Donnell
• Reporter: Stephen O'Donnell
• Created: 06/Aug/19 21:08
• Updated: 11/Aug/21 04:18
• Resolved: 02/Sep/19 17:09

Description

If a block and its meta file are corrupted in a certain way, the corruption can go unnoticed by a client, causing it to return invalid data.

The meta file is expected to always have a header of 7 bytes and then a series of checksums depending on the length of the block.

If the metafile gets corrupted in such a way, that it is between zero and less than 7 bytes in length, then the header is incomplete. In BlockSender.java the logic checks if the metafile length is at least the size of the header and if it is not, it does not error, but instead returns a NULL checksum type to the client.

https://github.com/apache/hadoop/blob/b77761b0e37703beb2c033029e4c0d5ad1dce794/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockSender.java#L327-L357

If the client receives a NULL checksum client, it will not validate checksums at all, and even corrupted data will be returned to the reader. This means this corrupt will go unnoticed and HDFS will never repair it. Even the Volume Scanner will not notice the corruption as the checksums are silently ignored.

Additionally, if the meta file does have enough bytes so it attempts to load the header, and the header is corrupted such that it is not valid, it can cause the datanode Volume Scanner to exit, which an exception like the following:

2019-08-06 18:16:39,151 ERROR datanode.VolumeScanner: VolumeScanner(/tmp/hadoop-sodonnell/dfs/data, DS-7f103313-61ba-4d37-b63d-e8cf7d2ed5f7) exiting because of exception 
java.lang.IllegalArgumentException: id=51 out of range [0, 5)
	at org.apache.hadoop.util.DataChecksum$Type.valueOf(DataChecksum.java:76)
	at org.apache.hadoop.util.DataChecksum.newDataChecksum(DataChecksum.java:167)
	at org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader.readHeader(BlockMetadataHeader.java:173)
	at org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader.readHeader(BlockMetadataHeader.java:139)
	at org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader.readHeader(BlockMetadataHeader.java:153)
	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.loadLastPartialChunkChecksum(FsVolumeImpl.java:1140)
	at org.apache.hadoop.hdfs.server.datanode.FinalizedReplica.loadLastPartialChunkChecksum(FinalizedReplica.java:157)
	at org.apache.hadoop.hdfs.server.datanode.BlockSender.getPartialChunkChecksumForFinalized(BlockSender.java:451)
	at org.apache.hadoop.hdfs.server.datanode.BlockSender.<init>(BlockSender.java:266)
	at org.apache.hadoop.hdfs.server.datanode.VolumeScanner.scanBlock(VolumeScanner.java:446)
	at org.apache.hadoop.hdfs.server.datanode.VolumeScanner.runLoop(VolumeScanner.java:558)
	at org.apache.hadoop.hdfs.server.datanode.VolumeScanner.run(VolumeScanner.java:633)
2019-08-06 18:16:39,152 INFO datanode.VolumeScanner: VolumeScanner(/tmp/hadoop-sodonnell/dfs/data, DS-7f103313-61ba-4d37-b63d-e8cf7d2ed5f7) exiting.

Issue Links

• is duplicated by: HDFS-16161 Corrupt block checksum is not reported to NameNode