commit 284956b5b123125c814bb3841c6871ddfb0694a3
author Alexei Podtelezhnikov <apodtele@gmail.com> Tue Jul 26 12:23:15 2022 -0400
committer Alexei Podtelezhnikov <apodtele@gmail.com> Tue Jul 26 12:23:15 2022 -0400
tree e3b01169a30f2eb2f873e61455964a4c2dbebf76
parent 182295cbcf63e0399f5df68f3d8a7e60b8eeecdb

[pfr] Fortify the kerning code.

Any array index must be strictly less then the array size. Therefore,
we must reject indexes that are equal to the array size.  Alternatively,
we should move the bounds check before the index decrement but that
would be confusing.

In addition, it is ok to decrement zero (.notdef) and get UINT_MAX,
which is then automatically rejected in the bounds check.

* src/pfr/pfrobjs.c (pfr_face_get_kerning): Fix the bounds checking.

src/pfr/pfrobjs.c

diff --git a/src/pfr/pfrobjs.c b/src/pfr/pfrobjs.c
index 8b29fc0..1457adc 100644
--- a/src/pfr/pfrobjs.c
+++ b/src/pfr/pfrobjs.c
@@ -486,17 +486,16 @@
     kerning->x = 0;
     kerning->y = 0;
 
-    if ( glyph1 > 0 )
-      glyph1--;
+    /* PFR indexing skips .notdef, which becomes UINT_MAX */
+    glyph1--;
+    glyph2--;
 
-    if ( glyph2 > 0 )
-      glyph2--;
-
-    /* convert glyph indices to character codes */
-    if ( glyph1 > phy_font->num_chars ||
-         glyph2 > phy_font->num_chars )
+    /* check the array bounds, .notdef is automacally out */
+    if ( glyph1 >= phy_font->num_chars ||
+         glyph2 >= phy_font->num_chars )
       goto Exit;
 
+    /* convert glyph indices to character codes */
     code1 = phy_font->chars[glyph1].char_code;
     code2 = phy_font->chars[glyph2].char_code;
     pair  = PFR_KERN_INDEX( code1, code2 );