diff options
| -rw-r--r-- | ffvisd/ffvisd.c | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/ffvisd/ffvisd.c b/ffvisd/ffvisd.c index 93e9b1b..d8ecf3d 100644 --- a/ffvisd/ffvisd.c +++ b/ffvisd/ffvisd.c @@ -133,6 +133,12 @@ static struct timespec now; static ffvisd_announce_t *announcements = NULL; +/* ones' complement add */ +static inline u_int16_t add16(u_int16_t a, u_int16_t b) { + a += b; + return a + (a < b); +} + static inline bool is_eth_addr_unspec(const eth_addr_t *address) { const uint8_t *a = address->address; @@ -447,6 +453,16 @@ static void maintenance() { } } +static uint16_t do_checksum(void *data, unsigned n_words) { + uint16_t ret = 0; + uint16_t *words = data; + + while(n_words) + ret = add16(ret, words[--n_words]); + + return ~ret; +} + static void send_announcement(const char *ifname, unsigned ifindex, void *arg) { char *if_mesh = iface_get_mesh(ifname); @@ -488,6 +504,8 @@ static void send_announcements() { packet->n_servers = htons(n_servers); + packet->csum = do_checksum(packet, (sizeof(ffvisd_packet_announce_t) + n_servers*sizeof(ffvisd_packet_server_announce_t))/2); + ffvisd_iface_foreach(send_announcement, packet); } @@ -513,6 +531,11 @@ static void receive_announcement() { return; } + if (do_checksum(packet, (sizeof(ffvisd_packet_announce_t) + n_servers*sizeof(ffvisd_packet_server_announce_t))/2)) { + fprintf(stderr, "warning: invalid checksum"); + return; + } + puts("Received announcements:"); int i; for(i = 0; i < n_servers; i++) |