nvmet-auth: allow to clear DH-HMAC-CHAP keys

As we can set DH-HMAC-CHAP keys, we should also be
able to unset them.
Signed-off-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/target/auth.c

@@ -25,6 +25,18 @@ int nvmet_auth_set_key(struct nvmet_host *host, const char *secret,
 	unsigned char key_hash;
 	char *dhchap_secret;
 
+	if (!strlen(secret)) {
+		if (set_ctrl) {
+			kfree(host->dhchap_ctrl_secret);
+			host->dhchap_ctrl_secret = NULL;
+			host->dhchap_ctrl_key_hash = 0;
+		} else {
+			kfree(host->dhchap_secret);
+			host->dhchap_secret = NULL;
+			host->dhchap_key_hash = 0;
+		}
+		return 0;
+	}
 	if (sscanf(secret, "DHHC-1:%hhd:%*s", &key_hash) != 1)
 		return -EINVAL;
 	if (key_hash > 3) {