From a3bab162b2ae616074c8877a04556932998aeacd Mon Sep 17 00:00:00 2001
From: Werner Lemberg <wl@gnu.org>
Date: Mon, 19 Oct 2020 23:45:28 +0200
Subject: [PATCH] [sfnt] Fix heap buffer overflow (#59308).

This is CVE-2020-15999.

* src/sfnt/pngshim.c (Load_SBit_Png): Test bitmap size earlier.
---
 ChangeLog          |  8 ++++++++
 src/sfnt/pngshim.c | 14 +++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/sfnt/pngshim.c b/src/sfnt/pngshim.c
index 2e64e5846..f55016122 100644
--- a/src/sfnt/pngshim.c
+++ b/src/sfnt/pngshim.c
@@ -332,6 +332,13 @@
 
     if ( populate_map_and_metrics )
     {
+      /* reject too large bitmaps similarly to the rasterizer */
+      if ( imgHeight > 0x7FFF || imgWidth > 0x7FFF )
+      {
+        error = FT_THROW( Array_Too_Large );
+        goto DestroyExit;
+      }
+
       metrics->width  = (FT_UShort)imgWidth;
       metrics->height = (FT_UShort)imgHeight;
 
@@ -340,13 +347,6 @@
       map->pixel_mode = FT_PIXEL_MODE_BGRA;
       map->pitch      = (int)( map->width * 4 );
       map->num_grays  = 256;
-
-      /* reject too large bitmaps similarly to the rasterizer */
-      if ( map->rows > 0x7FFF || map->width > 0x7FFF )
-      {
-        error = FT_THROW( Array_Too_Large );
-        goto DestroyExit;
-      }
     }
 
     /* convert palette/gray image to rgb */
-- 
2.26.2