efi: efivars: prevent double registration

Add the missing sanity check to efivars_register() so that it is no
longer possible to override an already registered set of efivar ops
(without first deregistering them).

This can help debug initialisation ordering issues where drivers have so
far unknowingly been relying on overriding the generic ops.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index f34e7741e0c36c462fd2ed7b82871f43e97be404..bd75b87f5fc1602d0d2da423e4aa3b372a3e08e4 100644 (file)
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -62,18 +62,27 @@ EXPORT_SYMBOL_GPL(efivar_is_available);
 int efivars_register(struct efivars *efivars,
                     const struct efivar_operations *ops)
 {
+       int rv;
+
        if (down_interruptible(&efivars_lock))
                return -EINTR;
 
+       if (__efivars) {
+               pr_warn("efivars already registered\n");
+               rv = -EBUSY;
+               goto out;
+       }
+
        efivars->ops = ops;
 
        __efivars = efivars;
 
        pr_info("Registered efivars operations\n");
-
+       rv = 0;
+out:
        up(&efivars_lock);
 
-       return 0;
+       return rv;
 }
 EXPORT_SYMBOL_GPL(efivars_register);