Fix minimum packet size

1 files changed, 4 insertions, 1 deletions

diff --git a/ffvisd/ffvisd.c b/ffvisd/ffvisd.c
index d1b36f0..93e9b1b 100644
--- a/ffvisd/ffvisd.c
+++ b/ffvisd/ffvisd.c
@@ -462,7 +462,8 @@ static void send_announcement(const char *ifname, unsigned ifindex, void *arg) {
 		sa.sll_halen = ETH_ALEN;
 		memcpy(sa.sll_addr, ffd_addr.address, ETH_ALEN);
 
-		sendto(sockfd, packet, sizeof(ffvisd_packet_announce_t) + ntohs(packet->n_servers)*sizeof(ffvisd_packet_server_announce_t), 0, (struct sockaddr*)&sa, sizeof(sa));
+		unsigned len = sizeof(ffvisd_packet_announce_t) + ntohs(packet->n_servers)*sizeof(ffvisd_packet_server_announce_t);
+		sendto(sockfd, packet, len > 46 ? len : 46, 0, (struct sockaddr*)&sa, sizeof(sa));
 	}
 	free(if_mesh);
 }
@@ -470,6 +471,8 @@ static void send_announcement(const char *ifname, unsigned ifindex, void *arg) {
 static void send_announcements() {
 	ffvisd_packet_announce_t *packet = alloca(sizeof(ffvisd_packet_announce_t) + 75*sizeof(ffvisd_packet_server_announce_t));
 
+	memset(packet, 0, 46); /* minimum ethernet packet size is 46 bytes */
+
 	packet->magic = htons(FFD_MAGIC);
 	packet->version = htons(FFVISD_VERSION);
 	packet->csum = 0;