check kern table size

Change-Id: I65b5f0a8950d54c00d6fd7c385ca1c5dca2ef2c8
Reviewed-on: https://gerrit.libreoffice.org/49384Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
(cherry picked from commit d566c200)

vcl/source/fontsubset/sft.cxx

@@ -1355,7 +1355,7 @@ static void GetKern(TrueTypeFont *ttf)
     if( !table )
         goto badtable;
 
-    if (GetUInt16(table, 0) == 0) {                                /* Traditional Microsoft style table with sal_uInt16 version and nTables fields */
+    if (nTableSize >= 4 && GetUInt16(table, 0) == 0) { /* Traditional Microsoft style table with sal_uInt16 version and nTables fields */
         ttf->nkern = GetUInt16(table, 2);
         ttf->kerntype = KT_MICROSOFT;
         ptr = table + 4;
@@ -1387,7 +1387,7 @@ static void GetKern(TrueTypeFont *ttf)
         return;
     }
 
-    if (GetUInt32(table, 0) == 0x00010000) {                       /* MacOS style kern tables: fixed32 version and sal_uInt32 nTables fields */
+    if (nTableSize >= 8 && GetUInt32(table, 0) == 0x00010000) { /* MacOS style kern tables: fixed32 version and sal_uInt32 nTables fields */
         ttf->nkern = GetUInt32(table, 4);
         ttf->kerntype = KT_APPLE_NEW;
         ptr = table + 8;