Add simple sshsig fuzzer

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Sahana Prasad <sahana@redhat.com>

tests/fuzz/ssh_sshsig_fuzzer.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2025 Jakub Jelen <jjelen@redhat.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LIBSSH_STATIC 1
+#include "libssh/libssh.h"
+
+static void _fuzz_finalize(void)
+{
+    ssh_finalize();
+}
+
+int LLVMFuzzerInitialize(int *argc, char ***argv)
+{
+    (void)argc;
+    (void)argv;
+
+    ssh_init();
+
+    atexit(_fuzz_finalize);
+
+    return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    ssh_key pkey = NULL;
+    const char input[] = "badc0de";
+    const char namespace[] = "namespace";
+    char *signature = NULL;
+    int rc;
+
+    signature = (char *)malloc(size + 1);
+    if (signature == NULL) {
+        return 1;
+    }
+    strncpy(signature, (const char *)data, size);
+    signature[size] = '\0';
+
+    rc = sshsig_verify(input, sizeof(input), signature, namespace, &pkey);
+    free(signature);
+    if (rc != SSH_OK) {
+        return 1;
+    }
+    ssh_key_free(pkey);
+
+    return 0;
+}