Add initial fuzzers to be used by oss-fuzz.

These are not yet hooked up to the sudo build.

plugins/sudoers/regress/fuzz/fuzz_sudoers.c

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2021 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * 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 <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#if defined(HAVE_STDINT_H)
+# include <stdint.h>
+#elif defined(HAVE_INTTYPES_H)
+# include <inttypes.h>
+#endif
+
+#include "sudoers.h"
+
+/* Required to link with parser. */
+struct sudo_user sudo_user;
+struct passwd *list_pw;
+
+FILE *
+open_sudoers(const char *file, bool doedit, bool *keepopen)
+{
+    return fopen(file, "r");
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    /* Don't waste time fuzzing tiny inputs. */
+    if (size < 5)
+        return 0;
+
+    /* Operate in-memory, do not fclose or it will free() data. */
+    sudoersin = fmemopen((void *)data, size, "r");
+    if (sudoersin == NULL)
+        return 0;
+
+    /* Initialize defaults and parse sudoers. */
+    init_defaults();
+    init_parser("sudoers", false, true);
+    sudoersparse();
+
+    return 0;
+}