Security: fix potential multiplication overflow

Better sanity check inputs to bit stream reader

ChangeLog

@@ -1,5 +1,8 @@
 2013-10-05  Jay Berkenbilt  <ejb@ql.org>
 
+	* Security fix: perform additional argument sanity checks when
+	reading bit streams.
+
 	* Security fix: in QUtil::toUTF8, change bounds checking to avoid
 	having a pointer point temporarily outside the bounds of an
 	array.  Some compiler optimizations could have made the original

libqpdf/BitStream.cc

@@ -16,6 +16,10 @@ BitStream::reset()
 {
     p = start;
     bit_offset = 7;
+    if (static_cast<unsigned int>(nbytes) > static_cast<unsigned int>(-1) / 8)
+    {
+	throw std::runtime_error("array too large for bitstream");
+    }
     bits_available = 8 * nbytes;
 }