8321802: (zipfs) Add validation of incorrect LOC signature in ZipFileSystem

src/jdk.zipfs/share/classes/jdk/nio/zipfs/ZipFileSystem.java

@@ -2573,7 +2573,10 @@ private void initDataPos() throws IOException {
                 pos = -pos + locpos;
                 byte[] buf = new byte[LOCHDR];
                 if (readNBytesAt(buf, 0, buf.length, pos) != LOCHDR) {
-                    throw new ZipException("invalid loc " + pos + " for entry reading");
+                    throw new ZipException("invalid LOC " + pos + " for entry reading");
+                }
+                if (LOCSIG(buf) != LOCSIG) {
+                    throw new ZipException("invalid LOC header (bad signature)");
                 }
                 pos += LOCHDR + LOCNAM(buf) + LOCEXT(buf);
             }

test/jdk/jdk/nio/zipfs/CorruptedZipFilesTest.java

@@ -22,7 +22,7 @@
  */
 
 /* @test
- * @bug 8316141
+ * @bug 8316141 8321802
  * @summary test for correct detection and reporting of corrupted zip files
  * @run junit CorruptedZipFilesTest
  */
@@ -287,6 +287,16 @@ public void unsupportedCompressionMethod() throws IOException {
         assertZipException(".*unsupported compression method.*");
     }
 
+    /*
+     * A ZipException is thrown when a LOC header has an unexpected signature
+     */
+    @Test
+    public void invalidLOCSignature() throws IOException {
+        int existingSignature = buffer.getInt(locpos);
+        buffer.putInt(locpos, existingSignature +1);
+        assertZipException(".*bad signature.*");
+    }
+
     /*
      * Assert that opening a ZIP file and consuming the entry's
      * InputStream using the ZipFile API fails with a ZipException