8066915: (fs) Files.newByteChannel opens directories for cases where subsequent reads may fail

Reviewed-by: chegar

jdk/src/java.base/unix/classes/sun/nio/fs/UnixChannelFactory.java

@@ -270,6 +270,22 @@ class UnixChannelFactory {
             throw x;
         }
 
+        // fail if the file is a directory
+        if (flags.read) {
+            UnixException exc = null;
+            try {
+                if (UnixFileAttributes.get(fd).isDirectory()) {
+                    exc = new UnixException(EISDIR);
+                }
+            } catch (UnixException x) {
+                exc = x;
+            }
+            if (exc != null) {
+                close(fd);
+                throw exc;
+            }
+        }
+
         // unlink file immediately if delete on close. The spec is clear that
         // an implementation cannot guarantee to unlink the correct file when
         // replaced by an attacker after it is opened.

jdk/test/java/nio/file/Files/SBC.java

@@ -22,7 +22,7 @@
  */
 
 /* @test
- * @bug 4313887
+ * @bug 4313887 8066915
  * @summary Unit test for java.nio.file.Files.newByteChannel
  * @library ..
  */
@@ -59,6 +59,7 @@ public class SBC {
                 dosSharingOptionTests(dir);
 
             // misc. tests
+            directoryOpenTests(dir);
             badCombinations(dir);
             unsupportedOptions(dir);
             nullTests(dir);
@@ -278,6 +279,21 @@ public class SBC {
         }
     }
 
+    // test opening a directory for read or write
+    static void directoryOpenTests(Path dir) throws Exception {
+        try (SeekableByteChannel sbc = Files.newByteChannel(dir, READ)) {
+            throw new RuntimeException("Opened directory for read");
+        } catch (IOException expected) { }
+
+        try (SeekableByteChannel sbc = Files.newByteChannel(dir, WRITE)) {
+            throw new RuntimeException("Opened directory for write");
+        } catch (IOException expected) { }
+
+        try (SeekableByteChannel sbc = Files.newByteChannel(dir, APPEND)) {
+            throw new RuntimeException("Opened directory for append ");
+        } catch (IOException expected) { }
+    }
+
     // Windows specific options for the use by applications that really want
     // to use legacy DOS sharing options
     static void dosSharingOptionTests(Path dir) throws Exception {