efivars: Respect "block" flag in efivar_entry_set_safe()

commit 258dd90 upstream.

When the "block" flag is false, the old code would sometimes still call
check_var_size(), which wrongly tells ->query_variable_store() that it can
block.

As far as I can tell, this can't really materialize as a bug at the moment,
because ->query_variable_store only does something on X86 with generic EFI,
and in that configuration we always take the efivar_entry_set_nonblocking()
path.

Fixes: ca0e30d ("efi: Add nonblocking option to efi_query_variable_store()")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220218180559.1432559-1-jannh@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/firmware/efi/vars.c

@@ -742,6 +742,7 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 {
 	const struct efivar_operations *ops;
 	efi_status_t status;
+	unsigned long varsize;
 
 	if (!__efivars)
 		return -EINVAL;
@@ -764,15 +765,17 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 		return efivar_entry_set_nonblocking(name, vendor, attributes,
 						    size, data);
 
+	varsize = size + ucs2_strsize(name, 1024);
 	if (!block) {
 		if (down_trylock(&efivars_lock))
 			return -EBUSY;
+		status = check_var_size_nonblocking(attributes, varsize);
 	} else {
 		if (down_interruptible(&efivars_lock))
 			return -EINTR;
+		status = check_var_size(attributes, varsize);
 	}
 
-	status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
 	if (status != EFI_SUCCESS) {
 		up(&efivars_lock);
 		return -ENOSPC;