diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 4912f50009b..f9837f339ff 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -932,6 +932,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-9022. Move NameNode.getAddress() and NameNode.getUri() to
     hadoop-hdfs-client. (Mingliang Liu via wheat9)
 
+    HDFS-5802. NameNode does not check for inode type before traversing down a
+    path. (Xiao Chen via Yongjun Zhang)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSPermissionChecker.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSPermissionChecker.java
index 041ce0b277a..9edcda13264 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSPermissionChecker.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSPermissionChecker.java
@@ -192,6 +192,25 @@ class FSPermissionChecker implements AccessControlEnforcer {
         ancestorAccess, parentAccess, access, subAccess, ignoreEmptyDir);
   }
 
+  /**
+   * Check whether exception e is due to an ancestor inode's not being
+   * directory.
+   */
+  private void checkAncestorType(INode[] inodes, int ancestorIndex,
+      AccessControlException e) throws AccessControlException {
+    for (int i = 0; i <= ancestorIndex; i++) {
+      if (inodes[i] == null) {
+        break;
+      }
+      if (!inodes[i].isDirectory()) {
+        throw new AccessControlException(
+            e.getMessage() + " (Ancestor " + inodes[i].getFullPathName()
+                + " is not a directory).");
+      }
+    }
+    throw e;
+  }
+
   @Override
   public void checkPermission(String fsOwner, String supergroup,
       UserGroupInformation callerUgi, INodeAttributes[] inodeAttrs,
@@ -202,7 +221,11 @@ class FSPermissionChecker implements AccessControlEnforcer {
       throws AccessControlException {
     for(; ancestorIndex >= 0 && inodes[ancestorIndex] == null;
         ancestorIndex--);
-    checkTraverse(inodeAttrs, path, ancestorIndex);
+    try {
+      checkTraverse(inodeAttrs, path, ancestorIndex);
+    } catch (AccessControlException e) {
+      checkAncestorType(inodes, ancestorIndex, e);
+    }
 
     final INodeAttributes last = inodeAttrs[inodeAttrs.length - 1];
     if (parentAccess != null && parentAccess.implies(FsAction.WRITE)
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSPermission.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSPermission.java
index 23ce916ae11..80b2eb44122 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSPermission.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSPermission.java
@@ -22,6 +22,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
+import java.io.DataOutputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.security.PrivilegedExceptionAction;
@@ -510,8 +511,45 @@ public class TestDFSPermission {
     }
   }
 
-  /* Check if namenode performs permission checking correctly 
-   * for the given user for operations mkdir, open, setReplication, 
+  @Test
+  public void testPermissionMessageOnNonDirAncestor()
+      throws IOException, InterruptedException {
+    FileSystem rootFs = FileSystem.get(conf);
+    Path p4 = new Path("/p4");
+    rootFs.mkdirs(p4);
+    rootFs.setOwner(p4, USER1_NAME, GROUP1_NAME);
+
+    final Path fpath = new Path("/p4/file");
+    DataOutputStream out = rootFs.create(fpath);
+    out.writeBytes("dhruba: " + fpath);
+    out.close();
+    rootFs.setOwner(fpath, USER1_NAME, GROUP1_NAME);
+    assertTrue(rootFs.exists(fpath));
+
+    fs = USER1.doAs(new PrivilegedExceptionAction<FileSystem>() {
+      @Override
+      public FileSystem run() throws Exception {
+        return FileSystem.get(conf);
+      }
+    });
+
+    final Path nfpath = new Path("/p4/file/nonexisting");
+    assertFalse(rootFs.exists(nfpath));
+
+    try {
+      fs.exists(nfpath);
+      fail("The exists call should have failed.");
+    } catch (AccessControlException e) {
+      assertTrue("Permission denied messages must carry file path",
+          e.getMessage().contains(fpath.getName()));
+      assertTrue("Permission denied messages must specify existing_file is not "
+              + "a directory, when checked on /existing_file/non_existing_name",
+          e.getMessage().contains("is not a directory"));
+    }
+  }
+
+  /* Check if namenode performs permission checking correctly
+   * for the given user for operations mkdir, open, setReplication,
    * getFileInfo, isDirectory, exists, getContentLength, list, rename,
    * and delete */
   private void testPermissionCheckingPerUser(UserGroupInformation ugi,