add dummy ssh-sk API for linking with fuzzers

regress/misc/fuzz-harness/ssh-sk-null.cc

@@ -0,0 +1,46 @@
+/* $OpenBSD$ */
+/*
+ * Copyright (c) 2019 Google LLC
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+
+#include "ssherr.h"
+#include "ssh-sk.h"
+
+int
+sshsk_sign(const char *provider, struct sshkey *key,
+    u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
+    u_int compat, const char *pin)
+{
+	return SSH_ERR_FEATURE_UNSUPPORTED;
+}
+
+int
+sshsk_enroll(int type, const char *provider_path, const char *application,
+    uint8_t flags, const char *pin, struct sshbuf *challenge_buf,
+    struct sshkey **keyp, struct sshbuf *attest)
+{
+	return SSH_ERR_FEATURE_UNSUPPORTED;
+}
+
+int
+sshsk_load_resident(const char *provider_path, const char *pin,
+    struct sshkey ***keysp, size_t *nkeysp)
+{
+	return SSH_ERR_FEATURE_UNSUPPORTED;
+}