From f3afa24da144409a3c3a0e35913112583d987671 Mon Sep 17 00:00:00 2001
From: Michal Srb <michalsrb@gmail.com>
Date: Mon, 27 Mar 2017 19:02:15 +0300
Subject: Prevent double free by crafted fences.

If client sent fence with some data, followed by fence with no data (length 0), the original fence data were freed, but the pointer kept pointing at them. Sending one more fence would attempt to free them again.
---
 common/rfb/SMsgWriter.cxx | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

(limited to 'common/rfb/SMsgWriter.cxx')

diff --git a/common/rfb/SMsgWriter.cxx b/common/rfb/SMsgWriter.cxx
index cf3264e8..bc3f4398 100644
--- a/common/rfb/SMsgWriter.cxx
+++ b/common/rfb/SMsgWriter.cxx
@@ -101,7 +101,9 @@ void SMsgWriter::writeFence(rdr::U32 flags, unsigned len, const char data[])
   os->writeU32(flags);
 
   os->writeU8(len);
-  os->writeBytes(data, len);
+
+  if (len > 0)
+    os->writeBytes(data, len);
 
   endMsg();
 }
-- 
cgit v1.2.3