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-rw-r--r--ffvisd/ffvisd.c23
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++)