conntrackd: add cthelper infrastructure (+ example FTP helper)

This patch adds the user-space helper infrastructure. It also
contains the implementation of the FTP helper in user-space.

There's one example file that you can use to configure conntrackd
as user-space connection tracking helper under:

 doc/helper/conntrackd.conf

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 76 insertions, 0 deletions

diff --git a/src/helpers.c b/src/helpers.c
new file mode 100644
index 0000000..3e4e6c8
--- /dev/null
+++ b/src/helpers.c
@@ -0,0 +1,76 @@
+/*
+ * (C) 2012 by Pablo Neira Ayuso <pablo@netfilter.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation (or any later at your option).
+ *
+ * This code has been sponsored by Vyatta Inc. <http://www.vyatta.com>
+ */
+
+#include "helper.h"
+
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <dlfcn.h>
+
+static LIST_HEAD(helper_list);
+
+void helper_register(struct ctd_helper *helper)
+{
+	list_add(&helper->head, &helper_list);
+}
+
+static struct ctd_helper *
+__helper_find(const char *helper_name, uint8_t l4proto)
+{
+	struct ctd_helper *cur, *helper = NULL;
+
+	list_for_each_entry(cur, &helper_list, head) {
+		if (strncmp(cur->name, helper_name, CTD_HELPER_NAME_LEN) != 0)
+			continue;
+
+		if (cur->l4proto != l4proto)
+			continue;
+
+		helper = cur;
+		break;
+	}
+	return helper;
+}
+
+struct ctd_helper *
+helper_find(const char *libdir_path,
+	    const char *helper_name, uint8_t l4proto, int flag)
+{
+	char path[PATH_MAX];
+	struct ctd_helper *helper;
+	struct stat sb;
+
+	helper = __helper_find(helper_name, l4proto);
+	if (helper != NULL)
+		return helper;
+
+	snprintf(path, sizeof(path), "%s/ct_helper_%s.so",
+		libdir_path, helper_name);
+
+	if (stat(path, &sb) != 0) {
+		if (errno == ENOENT)
+			return NULL;
+		fprintf(stderr, "%s: %s\n", path,
+			strerror(errno));
+		return NULL;
+	}
+
+	if (dlopen(path, flag) == NULL) {
+		fprintf(stderr, "%s: %s\n", path, dlerror());
+		return NULL;
+	}
+
+	return __helper_find(helper_name, l4proto);
+}