[freetype2] master b24cfc8: [sfnt] Sanitize cmap4 table better.

[Werner Lemberg]

branch: master
commit b24cfc8dcc8991f464782f91922c2772f393184d
Author: Werner Lemberg <wl@gnu.org>
Commit: Werner Lemberg <wl@gnu.org>

    [sfnt] Sanitize cmap4 table better.
    
    Fixes #1062.
    
    * src/sfnt/ttcmap.c (tt_cmap4_validate): Handle a too-small value of
    `length` gracefully.
---
 ChangeLog         |  9 +++++++++
 src/sfnt/ttcmap.c | 10 ++++++++++
 2 files changed, 19 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 1c61793..3b64ee7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2021-06-08  Werner Lemberg  <wl@gnu.org>
+
+       [sfnt] Sanitize cmap4 table better.
+
+       Fixes #1062.
+
+       * src/sfnt/ttcmap.c (tt_cmap4_validate): Handle a too-small value of
+       `length` gracefully.
+
 2021-06-08  Dominik Röttsches  <drott@chromium.org>
 
        [sfnt] Pointer validity check when reading COLR 'v1' layers
diff --git a/src/sfnt/ttcmap.c b/src/sfnt/ttcmap.c
index 45d9f92..b369d83 100644
--- a/src/sfnt/ttcmap.c
+++ b/src/sfnt/ttcmap.c
@@ -916,6 +916,16 @@
       length = (FT_UInt)( valid->limit - table );
     }
 
+    /* it also happens that the `length' field is too small; */
+    /* this is easy to correct                               */
+    if ( length < (FT_UInt)( valid->limit - table ) )
+    {
+      if ( valid->level >= FT_VALIDATE_PARANOID )
+        FT_INVALID_DATA;
+
+      length = (FT_UInt)( valid->limit - table );
+    }
+
     if ( length < 16 )
       FT_INVALID_TOO_SHORT;