From 09e8fc02f59f16e2583b34fe1a270c238bd9ffec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
Date: Mon, 7 Jan 2019 10:40:01 +0100
Subject: [PATCH] Limit lenght to INT_MAX bytes in
 rfbProcessFileTransferReadBuffer()

This ammends 15bb719c03cc70f14c36a843dcb16ed69b405707 fix for a heap
out-of-bound write access in rfbProcessFileTransferReadBuffer() when
reading a transfered file content in a server. The former fix did not
work on platforms with a 32-bit int type (expected by rfbReadExact()).

CVE-2018-15127
<https://github.com/LibVNC/libvncserver/issues/243>
<https://github.com/LibVNC/libvncserver/issues/273>
---
 libvncserver/rfbserver.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libvncserver/rfbserver.c b/libvncserver/rfbserver.c
index 7af84906..f2edbeea 100644
--- a/libvncserver/rfbserver.c
+++ b/libvncserver/rfbserver.c
@@ -88,6 +88,8 @@
 #include <errno.h>
 /* strftime() */
 #include <time.h>
+/* INT_MAX */
+#include <limits.h>
 
 #ifdef LIBVNCSERVER_WITH_WEBSOCKETS
 #include "rfbssl.h"
@@ -1472,8 +1474,11 @@ char *rfbProcessFileTransferReadBuffer(rfbClientPtr cl, uint32_t length)
        0XFFFFFFFF, i.e. SIZE_MAX for 32-bit systems. On 64-bit systems, a length of 0XFFFFFFFF
        will safely be allocated since this check will never trigger and malloc() can digest length+1
        without problems as length is a uint32_t.
+       We also later pass length to rfbReadExact() that expects a signed int type and
+       that might wrap on platforms with a 32-bit int type if length is bigger
+       than 0X7FFFFFFF.
     */
-    if(length == SIZE_MAX) {
+    if(length == SIZE_MAX || length > INT_MAX) {
 	rfbErr("rfbProcessFileTransferReadBuffer: too big file transfer length requested: %u", (unsigned int)length);
 	rfbCloseClient(cl);
 	return NULL;
