From 53dfdcd8198d2b3201a23c4bad9190519ba918db Mon Sep 17 00:00:00 2001

From: Werner Lemberg <wl@gnu.org>

Date: Thu, 17 Mar 2022 19:24:16 +0100

Subject: [PATCH] [sfnt] Avoid invalid face index.

Fixes #1138.

* src/sfnt/sfobjs.c (sfnt_init_face), src/sfnt/sfwoff2.c (woff2_open_font):

Check `face_index` before decrementing.

---

 src/sfnt/sfobjs.c  | 2 +-

 src/sfnt/sfwoff2.c | 2 +-

 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/sfnt/sfobjs.c b/src/sfnt/sfobjs.c

index f9d4d3858..9771c35df 100644

--- a/src/sfnt/sfobjs.c

+++ b/src/sfnt/sfobjs.c

@@ -566,7 +566,7 @@

     face_index = FT_ABS( face_instance_index ) & 0xFFFF;

     /* value -(N+1) requests information on index N */

-    if ( face_instance_index < 0 )

+    if ( face_instance_index < 0 && face_index > 0 )

       face_index--;

     if ( face_index >= face->ttc_header.count )

diff --git a/src/sfnt/sfwoff2.c b/src/sfnt/sfwoff2.c

index cb1e0664a..165b875e5 100644

--- a/src/sfnt/sfwoff2.c

+++ b/src/sfnt/sfwoff2.c

@@ -2085,7 +2085,7 @@

     /* Validate requested face index. */

     *num_faces = woff2.num_fonts;

     /* value -(N+1) requests information on index N */

-    if ( *face_instance_index < 0 )

+    if ( *face_instance_index < 0 && face_index > 0 )

       face_index--;

     if ( face_index >= woff2.num_fonts )

-- 

2.35.1