HDFS-7659. truncate should check negative value of the new length. Contributed by Yi Liu.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -497,6 +497,9 @@ Release 2.7.0 - UNRELEASED
     HDFS-7643. Test case to ensure lazy persist files cannot be truncated.
     (Yi Liu via Arpit Agarwal)
 
+    HDFS-7659. truncate should check negative value of the new length.
+    (Yi Liu via shv)
+
 Release 2.6.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -1991,6 +1991,10 @@ public class DFSClient implements java.io.Closeable, RemotePeerFactory,
    */
   public boolean truncate(String src, long newLength) throws IOException {
     checkOpen();
+    if (newLength < 0) {
+      throw new HadoopIllegalArgumentException(
+          "Cannot truncate to a negative file size: " + newLength + ".");
+    }
     try {
       return namenode.truncate(src, newLength, clientName);
     } catch (RemoteException re) {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -1965,6 +1965,10 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
       NameNode.stateChangeLog.debug("DIR* NameSystem.truncate: src="
           + src + " newLength=" + newLength);
     }
+    if (newLength < 0) {
+      throw new HadoopIllegalArgumentException(
+          "Cannot truncate to a negative file size: " + newLength + ".");
+    }
     HdfsFileStatus stat = null;
     FSPermissionChecker pc = getPermissionChecker();
     checkOperation(OperationCategory.WRITE);

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFileTruncate.java

@@ -34,6 +34,7 @@ import java.io.IOException;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.HadoopIllegalArgumentException;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.ContentSummary;
 import org.apache.hadoop.fs.FSDataOutputStream;
@@ -443,6 +444,14 @@ public class TestFileTruncate {
     } catch(IOException expected) {}
     out.close();
 
+    try {
+      fs.truncate(p, -1);
+      fail("Truncate must fail for a negative new length.");
+    } catch (HadoopIllegalArgumentException expected) {
+      GenericTestUtils.assertExceptionContains(
+          "Cannot truncate to a negative file size", expected);
+    }
+
     cluster.shutdownDataNodes();
     NameNodeAdapter.getLeaseManager(cluster.getNamesystem())
         .setLeasePeriod(LOW_SOFTLIMIT, LOW_HARDLIMIT);