Be defensive about overflows in stream objects

We use a lot of lengths given to us over the network, so be more
paranoid about them causing an overflow as otherwise an attacker
might trick us in to overwriting other memory.

This primarily affects the client which often gets lengths from the
server, but there are also some scenarios where the server might
theoretically be vulnerable.

Issue found by Pavel Cheremushkin from Kaspersky Lab.

1 files changed, 4 insertions, 2 deletions

diff --git a/common/rdr/ZlibInStream.cxx b/common/rdr/ZlibInStream.cxx
index e2f971c7..9fcfaf6b 100644
--- a/common/rdr/ZlibInStream.cxx
+++ b/common/rdr/ZlibInStream.cxx
@@ -113,8 +113,10 @@ size_t ZlibInStream::overrun(size_t itemSize, size_t nItems, bool wait)
       return 0;
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }