[SECURITY PATCH 115/117] gfxmenu/gui: Check printf() format in the gui_progress_bar and gui_label

[Daniel Kiper]

From: Thomas Frauendorfer | Miray Software <tf@miray.de>

The gui_progress_bar and gui_label components can display the timeout
value. The format string can be set through a theme file. This patch
adds a validation step to the format string.

If a user loads a theme file into the GRUB without this patch then
a GUI label with the following settings

  + label {
  ...
  id = "__timeout__"
  text = "%s"
  }

will interpret the current timeout value as string pointer and print the
memory at that position on the screen. It is not desired behavior.

Signed-off-by: Thomas Frauendorfer | Miray Software <tf@miray.de>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/gfxmenu/gui_label.c        | 4 ++++
 grub-core/gfxmenu/gui_progress_bar.c | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/grub-core/gfxmenu/gui_label.c b/grub-core/gfxmenu/gui_label.c
index a4c817891..1c190542a 100644
--- a/grub-core/gfxmenu/gui_label.c
+++ b/grub-core/gfxmenu/gui_label.c
@@ -193,6 +193,10 @@ label_set_property (void *vself, const char *name, const 
char *value)
           else if (grub_strcmp (value, "@KEYMAP_SHORT@") == 0)
            value = _("enter: boot, `e': options, `c': cmd-line");
           /* FIXME: Add more templates here if needed.  */
+
+         if (grub_printf_fmt_check(value, "%d") != GRUB_ERR_NONE)
+           value = ""; /* Unsupported format. */
+
          self->template = grub_strdup (value);
          self->text = grub_xasprintf (value, self->value);
        }
diff --git a/grub-core/gfxmenu/gui_progress_bar.c 
b/grub-core/gfxmenu/gui_progress_bar.c
index b128f0866..ace85a125 100644
--- a/grub-core/gfxmenu/gui_progress_bar.c
+++ b/grub-core/gfxmenu/gui_progress_bar.c
@@ -348,6 +348,9 @@ progress_bar_set_property (void *vself, const char *name, 
const char *value)
           Please use the shortest form available in you language.  */
        value = _("%ds");
 
+      if (grub_printf_fmt_check(value, "%d") != GRUB_ERR_NONE)
+       value = ""; /* Unsupported format. */
+
       self->template = grub_strdup (value);
     }
   else if (grub_strcmp (name, "font") == 0)
-- 
2.11.0