font: Fix integer overflow in ensure_comb_space()

In fact it can't overflow at all because glyph_id->ncomb is only 8-bit
wide. But let's keep safe if somebody changes the width of glyph_id->ncomb
in the future. This patch also fixes the inconsistency between
render_max_comb_glyphs and render_combining_glyphs when grub_malloc()
returns NULL.

Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/font/font.c b/grub-core/font/font.c
index a8576ffecbdde74758517e11a7e9870e56e0b083..9e3e0a94e34d7c9b3e8faab5006ced76f9d682ce 100644 (file)
--- a/grub-core/font/font.c
+++ b/grub-core/font/font.c
@@ -1468,14 +1468,18 @@ ensure_comb_space (const struct grub_unicode_glyph *glyph_id)
   if (glyph_id->ncomb <= render_max_comb_glyphs)
     return;
 
-  render_max_comb_glyphs = 2 * glyph_id->ncomb;
-  if (render_max_comb_glyphs < 8)
+  if (grub_mul (glyph_id->ncomb, 2, &render_max_comb_glyphs))
+    render_max_comb_glyphs = 0;
+  if (render_max_comb_glyphs > 0 && render_max_comb_glyphs < 8)
     render_max_comb_glyphs = 8;
   grub_free (render_combining_glyphs);
-  render_combining_glyphs = grub_malloc (render_max_comb_glyphs
-                                        * sizeof (render_combining_glyphs[0]));
+  render_combining_glyphs = (render_max_comb_glyphs > 0) ?
+    grub_calloc (render_max_comb_glyphs, sizeof (render_combining_glyphs[0])) : NULL;
   if (!render_combining_glyphs)
-    grub_errno = 0;
+    {
+      render_max_comb_glyphs = 0;
+      grub_errno = GRUB_ERR_NONE;
+    }
 }
 
 int