RFR [9]8134424: BlockDataInputStream.readUTFBody: examine sizing local StringBuffer with the given length

[Chris Hegarty]

On 08/02/16 21:54, Aleksey Shipilev wrote:
> ...
> Still, the corrupted stream may call readUTFBody(1L +
> Integer.MAX_VALUE), that yields initial capacity of -2147483648, which
> in turn fails StringBuilder(...) with NegativeArraySizeException. But I
> wonder if that is actually a valid UTF8 input, because you cannot have
> that large of a String...

Right. To retain existing behavior (negative sizes => empty string)
then we can just short-circuit this.

diff --git a/src/java.base/share/classes/java/io/ObjectInputStream.java 
b/src/java.base/share/classes/java/io/ObjectInputStream.java
--- a/src/java.base/share/classes/java/io/ObjectInputStream.java
+++ b/src/java.base/share/classes/java/io/ObjectInputStream.java
@@ -3144,7 +3144,12 @@
           * utflen bytes.
           */
          private String readUTFBody(long utflen) throws IOException {
-            StringBuilder sbuf = new StringBuilder();
+            if (utflen < 0)
+                return "";
+
+            // a reasonable initial capacity based on the UTF length
+            int initialCapacity = Math.min((int)utflen, 16384);
+            StringBuilder sbuf = new StringBuilder(initialCapacity);
              if (!blkmode) {
                  end = pos = 0;
              }


-Chris.