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Add checksum calculation and verification

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This commit is contained in:
Matthias Schiffer 2012-08-30 02:08:02 +02:00
parent de3da7a6e4
commit da750868b5
1 changed files with 23 additions and 0 deletions
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23
ffvisd/ffvisd.c
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@ -133,6 +133,12 @@ static struct timespec now;
static ffvisd_announce_t *announcements = NULL; 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) { static inline bool is_eth_addr_unspec(const eth_addr_t *address) {
const uint8_t *a = address->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) { static void send_announcement(const char *ifname, unsigned ifindex, void *arg) {
char *if_mesh = iface_get_mesh(ifname); char *if_mesh = iface_get_mesh(ifname);
@ -488,6 +504,8 @@ static void send_announcements() {
packet->n_servers = htons(n_servers); 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); ffvisd_iface_foreach(send_announcement, packet);
} }
@ -513,6 +531,11 @@ static void receive_announcement() {
return; 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:"); puts("Received announcements:");
int i; int i;
for(i = 0; i < n_servers; i++) for(i = 0; i < n_servers; i++)