fuzz: test NDisc packet with more low level functions

Also, test send back the test packet.

Co-authored-by: Evgeny Vereshchagin <evvers@ya.ru>

src/libsystemd-network/fuzz-ndisc-rs.c

@@ -9,22 +9,19 @@
 #include "alloc-util.h"
 #include "fd-util.h"
 #include "fuzz.h"
+#include "icmp6-packet.h"
 #include "icmp6-util-unix.h"
 #include "ndisc-internal.h"
+#include "ndisc-option.h"
 #include "socket-util.h"
 
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+static void test_with_sd_ndisc(const uint8_t *data, size_t size) {
         struct ether_addr mac_addr = {
                 .ether_addr_octet = {'A', 'B', 'C', '1', '2', '3'}
         };
         _cleanup_(sd_event_unrefp) sd_event *e = NULL;
         _cleanup_(sd_ndisc_unrefp) sd_ndisc *nd = NULL;
 
-        if (outside_size_range(size, 0, 2048))
-                return 0;
-
-        fuzz_setup_logging();
-
         assert_se(sd_event_new(&e) >= 0);
         assert_se(sd_ndisc_new(&nd) >= 0);
         assert_se(sd_ndisc_attach_event(nd, e, 0) >= 0);
@@ -35,6 +32,46 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         (void) sd_event_run(e, UINT64_MAX);
         assert_se(sd_ndisc_stop(nd) >= 0);
         close(test_fd[1]);
+}
 
+static void test_with_icmp6_packet(const uint8_t *data, size_t size) {
+        static const struct sockaddr_in6 dst = {
+                .sin6_family = AF_INET6,
+                .sin6_addr = IN6ADDR_ALL_ROUTERS_MULTICAST_INIT,
+        };
+
+        _cleanup_close_pair_ int fd_pair[2] = EBADF_PAIR;
+        _cleanup_(icmp6_packet_unrefp) ICMP6Packet *packet = NULL;
+        _cleanup_set_free_ Set *options = NULL;
+
+        assert_se(socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, fd_pair) >= 0);
+        assert_se(write(fd_pair[1], data, size) == (ssize_t) size);
+
+        if (icmp6_packet_receive(fd_pair[0], &packet) < 0)
+                return;
+
+        if (ndisc_parse_options(packet, &options) < 0)
+                return;
+
+        if (ndisc_send(fd_pair[1], &dst, icmp6_packet_get_header(packet), options) < 0)
+                return;
+
+        packet = icmp6_packet_unref(packet);
+        options = set_free(options);
+
+        if (icmp6_packet_receive(fd_pair[0], &packet) < 0)
+                return;
+
+        (void) ndisc_parse_options(packet, &options);
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        if (outside_size_range(size, 0, 2048))
+                return 0;
+
+        fuzz_setup_logging();
+
+        test_with_sd_ndisc(data, size);
+        test_with_icmp6_packet(data, size);
         return 0;
 }