[PATCH] Avoid crash on empty menu

[Christian Franke]

If grub.cfg does not contain any valid menuentry statements, an empty 
menu is opened.
grub-emu crashes (and real grub behaves "interesting") if the first 
entry is selected.

The attached patch adds the missing nullptr checks.

An alternative would be to treat an empty menu as a syntax error in 
main.c::read_config_file(), at least if !nested.


During testing, I found the following issues:

- If the file does not exist, read_config_file() produces a memory leak, 
because newmenu is allocated first.

- The commands "source FILE" and "configfile FILE" open a nested normal 
mode shell (and produce this leak) if the file is missing. An error 
message should IMO be printed instead.

- The sequence "c" -> "rescue" -> "normal" appends the same entries to 
the existing menu, because the old entry is reused from "menu" data slot.

Thanks for any comment.

Christian

2007-11-07  Christian Franke  <address@hidden>

        * normal/menu.c (menu_run): Check for empty menu to avoid crash.
        (grub_run_menu): Likewise.


--- grub2.orig/normal/menu.c    2007-08-20 16:35:20.000000000 +0200
+++ grub2/normal/menu.c 2007-11-07 21:57:44.375000000 +0100
@@ -412,7 +412,11 @@ run_menu (grub_menu_t menu, int nested)
              goto refresh;
 
            case 'e':
-             grub_menu_entry_run (get_entry (menu, first + offset));
+               {
+                 grub_menu_entry_t e = get_entry (menu, first + offset);
+                 if (e)
+                   grub_menu_entry_run (e);
+               }
              goto refresh;
              
            default:
@@ -451,10 +455,13 @@ grub_menu_run (grub_menu_t menu, int nes
       if (boot_entry < 0)
        break;
 
+      e = get_entry (menu, boot_entry);
+      if (! e)
+       continue; /* menu is empty */
+       
       grub_cls ();
       grub_setcursor (1);
 
-      e = get_entry (menu, boot_entry);
       grub_printf ("  Booting \'%s\'\n\n", e->title);
   
       run_menu_entry (e);