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CASSANDRA-21412: Journal compaction did not get a reference to segments to segfault due to use-after-free #4852

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CASSANDRA-21412: Journal compaction did not get a reference to segments to segfault due to use-after-free #4852

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25 changes: 25 additions & 0 deletions src/java/org/apache/cassandra/journal/Compactor.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
Expand All @@ -29,6 +30,7 @@

import org.apache.cassandra.concurrent.ScheduledExecutorPlus;
import org.apache.cassandra.concurrent.Shutdownable;
import org.apache.cassandra.utils.concurrent.Ref;
import org.apache.cassandra.utils.concurrent.WaitQueue;

import static org.apache.cassandra.concurrent.ExecutorFactory.Global.executorFactory;
Expand Down Expand Up @@ -87,6 +89,24 @@ public void run()
toCompact.subList(limit, toCompact.size()).clear();
}

// Hold refs on all segments to prevent them from being cleaned up (mmap unmapped)
// while the compactor is still reading from them. Segments whose ref can't be
// acquired have already been released and must be skipped.
List<Ref<Segment<K, V>>> refs = new ArrayList<>(toCompact.size());
Iterator<StaticSegment<K, V>> it = toCompact.iterator();
while (it.hasNext())
{
StaticSegment<K, V> segment = it.next();
Ref<Segment<K, V>> ref = segment.tryRef();
if (ref == null)
it.remove();
else
refs.add(ref);
}

if (toCompact.isEmpty())
return;

try
{
Collection<StaticSegment<K, V>> newSegments = segmentCompactor.compact(toCompact);
Expand All @@ -104,6 +124,11 @@ public void run()
{
throw new RuntimeException("Could not compact segments: " + toCompact);
}
finally
{
for (Ref<Segment<K, V>> ref : refs)
ref.release();
}
}

@Override
Expand Down