trusted-keys: check for NULL before using it

TSS_rawhmac() checks for data != NULL before using it.
We should do the same thing for TSS_authhmac().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/keys/trusted_defined.c

@@ -148,6 +148,11 @@ static int TSS_authhmac(unsigned char *digest, const unsigned char *key,
 		if (dlen == 0)
 			break;
 		data = va_arg(argp, unsigned char *);
+		if (!data) {
+			ret = -EINVAL;
+			va_end(argp);
+			goto out;
+		}
 		ret = crypto_shash_update(&sdesc->shash, data, dlen);
 		if (ret < 0) {
 			va_end(argp);