From 93f9faad751c3069f828dd8d517814b8bf1d0084 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Wed, 16 Nov 2016 20:41:39 +0200
Subject: vmncdec: Sanity-check width/height before using it

We will allocate a screen area of width*height*bpp bytes, however this
calculation can easily overflow if too high width or height are given
inside the stream. Nonetheless we would just assume that enough memory
was allocated, try to fill it and overwrite as much memory as wanted.

Also allocate the screen area filled with zeroes to ensure that we start
with full-black and not any random (or not so random) data.

https://scarybeastsecurity.blogspot.gr/2016/11/0day-poc-risky-design-decisions-in.html

Ideally we should just remove this plugin in favour of the one in
gst-libav, which generally seems to be of better code quality.

https://bugzilla.gnome.org/show_bug.cgi?id=774533

diff --git a/gst/vmnc/vmncdec.c b/gst/vmnc/vmncdec.c
index e8d498c..b3c9778 100644
--- a/gst/vmnc/vmncdec.c
+++ b/gst/vmnc/vmncdec.c
@@ -260,7 +260,7 @@ vmnc_handle_wmvi_rectangle (GstVMncDec * dec, struct RfbRectangle *rect,
   gst_video_codec_state_unref (state);
 
   g_free (dec->imagedata);
-  dec->imagedata = g_malloc (dec->format.width * dec->format.height *
+  dec->imagedata = g_malloc0 (dec->format.width * dec->format.height *
       dec->format.bytes_per_pixel);
   GST_DEBUG_OBJECT (dec, "Allocated image data at %p", dec->imagedata);
 
@@ -790,6 +790,10 @@ vmnc_handle_packet (GstVMncDec * dec, const guint8 * data, int len,
             GST_WARNING_OBJECT (dec, "Rectangle out of range, type %d", r.type);
             return ERROR_INVALID;
           }
+        } else if (r.width > 16384 || r.height > 16384) {
+          GST_WARNING_OBJECT (dec, "Width or height too high: %ux%u", r.width,
+              r.height);
+          return ERROR_INVALID;
         }
 
         switch (r.type) {
-- 
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