package/libvncserver: fix CVE-2019-20788

libvncclient/cursor.c in LibVNCServer through 0.9.12 has a
HandleCursorShape integer overflow and heap-based buffer overflow via a
large height or width value. NOTE: this may overlap CVE-2019-15690.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libvncserver/0006-libvncclient-cursor-limit-width-height-input-values.patch

@@ -0,0 +1,40 @@
+From 54220248886b5001fbbb9fa73c4e1a2cb9413fed Mon Sep 17 00:00:00 2001
+From: Christian Beier <dontmind@freeshell.org>
+Date: Sun, 17 Nov 2019 17:18:35 +0100
+Subject: [PATCH] libvncclient/cursor: limit width/height input values
+
+Avoids a possible heap overflow reported by Pavel Cheremushkin
+<Pavel.Cheremushkin@kaspersky.com>.
+
+re #275
+
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+[Retrieved from:
+https://github.com/LibVNC/libvncserver/commit/54220248886b5001fbbb9fa73c4e1a2cb9413fed]
+---
+ libvncclient/cursor.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/libvncclient/cursor.c b/libvncclient/cursor.c
+index 67f45726..40ffb3b0 100644
+--- a/libvncclient/cursor.c
++++ b/libvncclient/cursor.c
+@@ -28,6 +28,8 @@
+ #define OPER_SAVE     0
+ #define OPER_RESTORE  1
+ 
++#define MAX_CURSOR_SIZE 1024
++
+ #define RGB24_TO_PIXEL(bpp,r,g,b)                                       \
+    ((((uint##bpp##_t)(r) & 0xFF) * client->format.redMax + 127) / 255             \
+     << client->format.redShift |                                              \
+@@ -54,6 +56,9 @@ rfbBool HandleCursorShape(rfbClient* client,int xhot, int yhot, int width, int h
+   if (width * height == 0)
+     return TRUE;
+ 
++  if (width >= MAX_CURSOR_SIZE || height >= MAX_CURSOR_SIZE)
++    return FALSE;
++
+   /* Allocate memory for pixel data and temporary mask data. */
+   if(client->rcSource)
+     free(client->rcSource);

package/libvncserver/libvncserver.mk

@@ -19,6 +19,9 @@ LIBVNCSERVER_IGNORE_CVES += CVE-2018-20750
 # 0004-rfbserver-don-t-leak-stack-memory-to-the-remote.patch
 LIBVNCSERVER_IGNORE_CVES += CVE-2019-15681
 
+# 0006-libvncclient-cursor-limit-width-height-input-values.patch
+LIBVNCSERVER_IGNORE_CVES += CVE-2019-20788
+
 # only used for examples
 LIBVNCSERVER_CONF_OPTS += \
 	-DWITH_FFMPEG=OFF \