Avoid infloops in font_open_entity

* src/font.c (font_open_entity): Fail after 15 iterations through
the loop that looks for a font whose average_width and height are
both positive.  This avoids infinite loops for fonts that, e.g.,
report average_width of zero for any possible size we try.
(Bug#31316)

(cherry picked from commit e2879c1f837059335af89022b2a9ac9bc861e96d)

1 files changed, 3 insertions, 0 deletions

diff --git a/src/font.c b/src/font.c
index a6d3f5d4798..e53935a15cc 100644
--- a/src/font.c
+++ b/src/font.c
@@ -2906,6 +2906,9 @@ font_open_entity (struct frame *f, Lisp_Object entity, int pixel_size)
       font = XFONT_OBJECT (font_object);
       if (font->average_width > 0 && font->height > 0)
         break;
+      /* Avoid an infinite loop.  */
+      if (psize > pixel_size + 15)
+        return Qnil;
     }
   ASET (font_object, FONT_SIZE_INDEX, make_number (pixel_size));
   FONT_ADD_LOG ("open", entity, font_object);