Commit 3829fdaae5f12590f93807e9bcb866be131a201a
2023-08-04T11:41:23
Avoid overflow in COLR bounds checks. The values read into `base_glyphs_offset_v1` and `layer_offset_v1` may be in the range 0xFFFFFFFD-0xFFFFFFFF. On systems where `unsigned long` is 32 bits adding 4 to such values will wrap and pass bounds checks but accessing values at such offsets will be out of bounds. On the other hand `table_size` has already been tested to be at least `COLRV1_HEADER_SIZE` (34) so it is safe to subtract 4 from it. * src/sfnt/ttcolr.c (tt_face_load_colr): subtract 4 from `table_size` instead of adding 4 to font data offsets in bounds checks Fixes: https://crbug.com/1469348
diff --git a/src/sfnt/ttcolr.c b/src/sfnt/ttcolr.c
index 69ccf0e..281e713 100644
--- a/src/sfnt/ttcolr.c
+++ b/src/sfnt/ttcolr.c
@@ -229,7 +229,7 @@
base_glyphs_offset_v1 = FT_NEXT_ULONG( p );
- if ( base_glyphs_offset_v1 + 4 >= table_size )
+ if ( base_glyphs_offset_v1 >= table_size - 4 )
goto InvalidTable;
p1 = (FT_Byte*)( table + base_glyphs_offset_v1 );
@@ -249,7 +249,7 @@
if ( layer_offset_v1 )
{
- if ( layer_offset_v1 + 4 >= table_size )
+ if ( layer_offset_v1 >= table_size - 4 )
goto InvalidTable;
p1 = (FT_Byte*)( table + layer_offset_v1 );