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  1. Cassandra
  2. CASSANDRA-8052

OOMs from allocating large arrays when deserializing (e.g probably corrupted EstimatedHistogram data)



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      We've seen nodes with what are presumably corrupted sstables repeatedly OOM on attempted startup with such a message:

      java.lang.OutOfMemoryError: Java heap space
       at org.apache.cassandra.utils.EstimatedHistogram$EstimatedHistogramSerializer.deserialize(EstimatedHistogram.java:266) 
      at org.apache.cassandra.io.sstable.SSTableMetadata$SSTableMetadataSerializer.deserialize(SSTableMetadata.java:292)
       at org.apache.cassandra.io.sstable.SSTableMetadata$SSTableMetadataSerializer.deserialize(SSTableMetadata.java:282)
       at org.apache.cassandra.io.sstable.SSTableReader.openMetadata(SSTableReader.java:234)
       at org.apache.cassandra.io.sstable.SSTableReader.open(SSTableReader.java:194)
       at org.apache.cassandra.io.sstable.SSTableReader.open(SSTableReader.java:157)
       at org.apache.cassandra.io.sstable.SSTableReader$1.run(SSTableReader.java:273)
       at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
       at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
       at java.util.concurrent.FutureTask.run(FutureTask.java:166)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
       at java.lang.Thread.run(Thread.java:722)

      It's probably not a coincidence that it's throwing an exception here since this seems to be the first byte of the file read.

      Presumably the correct operational process is just to replace the node,
      however I was wondering if generally we might want to validate lengths when we deserialise things?
      This could avoid allocating large byte buffers causing unpredictable OOMs and instead throw an exception to be handled as appropriate.

      In this particular instance, there is no need for an unduly large size for the estimated histogram.
      Admittedly things are slightly different in 2.1, though I suspect a similar thing might have happened with:

             int numComponents = in.readInt();
             // read toc
             Map<MetadataType, Integer> toc = new HashMap<>(numComponents); 

      Doing a find usages of DataInputStream.readInt() reveals quite a few places where an int is read in and then an ArrayList, array or map of that size is created.
      In some cases this size might validly vary over a java int,
      or be in a performance critical or delicate piece of code where one doesn't want such checks.
      Also there are other checksums and mechanisms at play which make some input less likely to be corrupted.

      However, is it maybe worth a pass over instances of this type of input, to try and avoid such cases where it makes sense?
      Perhaps there are less likely but worse failure modes present and hidden?
      E.g if the deserialisation is happens to be for a message sent to some or all nodes say.


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              mbyrd Matt Byrd
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