unhook_system_services: bail on systab == NULL

Prevent unhook_system_services() from dereferencing a NULL systab, which
may occur if hook_system_services() has never been called.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

diff --git a/replacements.c b/replacements.c
index 48dc43785e2d6a5c3684e1ee78870db10634efd0..5dfa3556718453b18b505d0c156c7b35626a2cde 100644 (file)
--- a/replacements.c
+++ b/replacements.c
@@ -70,6 +70,9 @@ static EFI_HANDLE last_loaded_image;
 void
 unhook_system_services(void)
 {
+       if (!systab)
+               return;
+
        systab->BootServices->Exit = system_exit;
        systab->BootServices->LoadImage = system_load_image;
        systab->BootServices->StartImage = system_start_image;