zebra: Add code for fuzzing netlink

This code allows you to fuzz the netlink listening socket
in zebra by --enable-fuzzing and passing the -w [FILE]
option when running zebra.

File collection is stored in /var/run/frr/netlink_*
where each number is just a counter to keep the
files distinct.

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>

zebra/kernel_netlink.c

@@ -20,6 +20,11 @@
 
 #include <zebra.h>
 
+#if defined(HANDLE_ZAPI_FUZZING)
+#include <stdio.h>
+#include <string.h>
+#endif
+
 #ifdef HAVE_NETLINK
 
 #include "linklist.h"
@@ -293,6 +298,97 @@ static int netlink_information_fetch(struct nlmsghdr *h, ns_id_t ns_id,
 	return 0;
 }
 
+#if defined(HANDLE_ZAPI_FUZZING)
+/* Using globals here to avoid adding function parameters */
+
+/* Keep distinct filenames for netlink fuzzy collection */
+static unsigned int netlink_file_counter = 1;
+
+/* File name to read fuzzed netlink from */
+static char netlink_fuzz_file[MAXPATHLEN] = "";
+
+/* Flag for whether to read from file or not */
+static int netlink_read = 0;
+
+/**
+ * netlink_set_read() - Sets the read flag
+ * @flag:      Flag value.
+ *
+ */
+void set_netlink_read(int flag)
+{
+	netlink_read = flag;
+}
+
+/**
+ * netlink_read_init() - Starts the message parser
+ * @fname:      Filename to read.
+ */
+void netlink_read_init(const char *fname)
+{
+	snprintf(netlink_fuzz_file, MAXPATHLEN, "%s", fname);
+	/* Creating this fake socket for testing purposes */
+	struct zebra_ns zns = {
+		.ns_id = 0,
+		.netlink_cmd = {.sock = -1,
+				.seq = -1,
+				.name = "fuzzer_command_channel"},
+		.netlink = {.sock = -1,
+			    .seq = -1,
+			    .name = "fuzzer_kernel_message"}
+	};
+	netlink_parse_info(netlink_information_fetch, &zns.netlink, &zns, 1, 0);
+}
+
+/**
+ * netlink_write_incoming() - Writes all data received from netlink to a file
+ * @buf:        Data from netlink.
+ * @size:       Size of data.
+ * @counter:    Counter for keeping filenames distinct.
+ */
+static void netlink_write_incoming(const char *buf, const unsigned int size,
+				   unsigned int counter)
+{
+	char fname[MAXPATHLEN];
+	FILE *f;
+
+	zserv_privs.change(ZPRIVS_RAISE);
+	snprintf(fname, MAXPATHLEN, "%s/%s_%u", DAEMON_VTY_DIR, "netlink",
+		 counter);
+	f = fopen(fname, "w");
+	if (f) {
+		fwrite(buf, 1, size, f);
+		fclose(f);
+	}
+	zserv_privs.change(ZPRIVS_LOWER);
+}
+
+/**
+ * netlink_read_file() - Reads netlink data from file
+ * @buf:        Netlink buffer being overwritten.
+ * @fname:      File name to read from.
+ *
+ * Return:      Size of file.
+ */
+static long netlink_read_file(char *buf, const char *fname)
+{
+	FILE *f;
+	long file_bytes = -1;
+	zserv_privs.change(ZPRIVS_RAISE);
+	f = fopen(fname, "r");
+	if (f) {
+		fseek(f, 0, SEEK_END);
+		file_bytes = ftell(f);
+		rewind(f);
+		fread(buf, file_bytes, 1, f);
+		fclose(f);
+	}
+	zserv_privs.change(ZPRIVS_LOWER);
+	return file_bytes;
+}
+
+#endif
+
 static int kernel_read(struct thread *thread)
 {
 	struct zebra_ns *zns = (struct zebra_ns *)THREAD_ARG(thread);
@@ -602,7 +698,18 @@ int netlink_parse_info(int (*filter)(struct nlmsghdr *, ns_id_t, int),
 		if (count && read_in >= count)
 			return 0;
 
+#if defined(HANDLE_ZAPI_FUZZING)
+		/* Check if reading and filename is set */
+		if (netlink_read && '\0' != netlink_fuzz_file[0]) {
+			zlog_debug("Reading netlink fuzz file");
+			status = netlink_read_file(buf, netlink_fuzz_file);
+			snl.nl_pid = 0;
+		} else {
 			status = recvmsg(nl->sock, &msg, 0);
+		}
+#else
+		status = recvmsg(nl->sock, &msg, 0);
+#endif
 		if (status < 0) {
 			if (errno == EINTR)
 				continue;
@@ -636,6 +743,14 @@ int netlink_parse_info(int (*filter)(struct nlmsghdr *, ns_id_t, int),
 			zlog_hexdump(buf, status);
 		}
 
+#if defined(HANDLE_ZAPI_FUZZING)
+		if (!netlink_read) {
+			zlog_debug("Writing incoming netlink message");
+			netlink_write_incoming(buf, status,
+					       netlink_file_counter++);
+		}
+#endif
+
 		read_in++;
 		for (h = (struct nlmsghdr *)buf;
 		     NLMSG_OK(h, (unsigned int)status);

zebra/kernel_netlink.h

@@ -45,6 +45,10 @@ extern const char *nl_rtproto_to_str(uint8_t rtproto);
 extern const char *nl_family_to_str(uint8_t family);
 extern const char *nl_rttype_to_str(uint8_t rttype);
 
+#if defined(HANDLE_ZAPI_FUZZING)
+extern void set_netlink_read(int flag);
+extern void netlink_read_init(const char *fname);
+#endif
 extern int netlink_parse_info(int (*filter)(struct nlmsghdr *, ns_id_t, int),
 			      struct nlsock *nl, struct zebra_ns *zns,
 			      int count, int startup);

zebra/main.c

@@ -54,6 +54,10 @@
 #include "zebra/zebra_rnh.h"
 #include "zebra/zebra_pbr.h"
 
+#if defined(HANDLE_ZAPI_FUZZING)
+#include "zebra/kernel_netlink.h"
+#endif
+
 #define ZEBRA_PTM_SUPPORT
 
 /* Zebra instance */
@@ -213,7 +217,8 @@ int main(int argc, char **argv)
 	struct sockaddr_storage dummy;
 	socklen_t dummylen;
 #if defined(HANDLE_ZAPI_FUZZING)
-	char *fuzzing = NULL;
+	char *zapi_fuzzing = NULL;
+	char *netlink_fuzzing = NULL;
 #endif
 
 	vrf_configure_backend(VRF_BACKEND_VRF_LITE);
@@ -227,7 +232,7 @@ int main(int argc, char **argv)
 		"s:n"
 #endif
 #if defined(HANDLE_ZAPI_FUZZING)
-		"c:"
+		"c:w:"
 #endif
 		,
 		longopts,
@@ -244,7 +249,8 @@ int main(int argc, char **argv)
 		"      --v6-rr-semantics Use v6 RR semantics\n"
 #endif /* HAVE_NETLINK */
 #if defined(HANDLE_ZAPI_FUZZING)
-		"  -c <file>             Bypass normal startup and use this file for testing of zapi"
+		"  -c <file>             Bypass normal startup and use this file for testing of zapi\n"
+		"  -w <file>             Bypass normal startup and use this file for testing of netlink input"
 #endif
 	);
 
@@ -306,7 +312,16 @@ int main(int argc, char **argv)
 #endif /* HAVE_NETLINK */
 #if defined(HANDLE_ZAPI_FUZZING)
 		case 'c':
-			fuzzing = optarg;
+			zapi_fuzzing = optarg;
+			set_netlink_read(1);
+			break;
+		case 'w':
+			netlink_fuzzing = optarg;
+			/* This ensures we are aren't writing any of the
+			 * startup netlink messages that happen when we
+			 * just want to read.
+			 */
+			set_netlink_read(1);
 			break;
 #endif
 		default:
@@ -349,6 +364,7 @@ int main(int argc, char **argv)
 /* For debug purpose. */
 /* SET_FLAG (zebra_debug_event, ZEBRA_DEBUG_EVENT); */
 
+
 	/* Process the configuration file. Among other configuration
 	*  directives we can meet those installing static routes. Such
 	*  requests will not be executed immediately, but queued in
@@ -385,8 +401,11 @@ int main(int argc, char **argv)
 	zebra_rnh_init();
 
 #if defined(HANDLE_ZAPI_FUZZING)
-	if (fuzzing) {
+	if (zapi_fuzzing) {
-		zserv_read_file(fuzzing);
+		zserv_read_file(zapi_fuzzing);
+		exit(0);
+	} else if (netlink_fuzzing) {
+		netlink_read_init(netlink_fuzzing);
 		exit(0);
 	}
 #endif