[woff2] Check whether known tag is in array bounds.

If table tag is not 0x3f, we expect a value between 0 and 62. If this is
not the case, exit with errors.

* src/sfnt/sfwoff2/c: Check whether table tag makes sense.

* src/sfnt/woff2tags.c: Return 0 if tag is out of bounds.

src/sfnt/sfwoff2.c

@@ -1760,7 +1760,15 @@
           goto Exit;
       }
       else
+      {
         table->Tag = woff2_known_tags( table->FlagByte & 0x3f );
+        if ( !table->Tag )
+        {
+          FT_ERROR(( "woff2_open_font: Unknown table tag." ));
+          error = FT_THROW( Invalid_Table );
+          goto Exit;
+        }
+      }
 
       flags = 0;
       xform_version = ( table->FlagByte >> 6 ) & 0x03;
@@ -1787,7 +1795,7 @@
           goto Exit;
         if ( table->Tag == TTAG_loca && table->TransformLength )
         {
-          FT_ERROR(( "woff_font_open: Invalid loca `transformLength'.\n" ));
+          FT_ERROR(( "woff2_open_font: Invalid loca `transformLength'.\n" ));
           error = FT_THROW( Invalid_Table );
           goto Exit;
         }
@@ -1795,7 +1803,7 @@
 
       if ( src_offset + table->TransformLength < src_offset )
       {
-        FT_ERROR(( "woff_font_open: invalid WOFF2 table directory.\n" ));
+        FT_ERROR(( "woff2_open_font: invalid WOFF2 table directory.\n" ));
         error = FT_THROW( Invalid_Table );
         goto Exit;
       }

src/sfnt/woff2tags.c

@@ -91,6 +91,9 @@
     };
 
 
+    if ( index < 0 || index > 62 )
+      return 0;
+
     return known_tags[index];
   }