Configurable SO_RCVBUF/SO_SNDBUF for the UDP socket

doc/tinc.conf.5.in

@@ -356,6 +356,14 @@ and will only allow connections with nodes for which host config files are prese
 .Pa @sysconfdir@/tinc/ Ns Ar NETNAME Ns Pa /hosts/
 directory.
 Setting this options also implicitly sets StrictSubnets.
+
+.It Va UDPRcvBuf Li = Ar bytes Pq OS default
+Sets the socket receive buffer size for the UDP socket, in bytes.
+If unset, the default buffer size will be used by the operating system.
+
+.It Va UDPSndBuf Li = Ar bytes Pq OS default
+Sets the socket send buffer size for the UDP socket, in bytes.
+If unset, the default buffer size will be used by the operating system.
 .El
 
 .Sh HOST CONFIGURATION FILES

src/net.h

@@ -111,6 +111,8 @@ extern listen_socket_t listen_socket[MAXSOCKETS];
 extern int listen_sockets;
 extern int keyexpires;
 extern int keylifetime;
+extern int udp_rcvbuf;
+extern int udp_sndbuf;
 extern bool do_prune;
 extern bool do_purge;
 extern char *myport;

src/net_setup.c

@@ -405,6 +405,20 @@ bool setup_myself(void) {
 	} else
 		maxtimeout = 900;
 
+	if(get_config_int(lookup_config(config_tree, "UDPRcvBuf"), &udp_rcvbuf)) {
+		if(udp_rcvbuf <= 0) {
+			logger(LOG_ERR, "UDPRcvBuf cannot be negative!");
+			return false;
+		}
+	}
+
+	if(get_config_int(lookup_config(config_tree, "UDPSndBuf"), &udp_sndbuf)) {
+		if(udp_sndbuf <= 0) {
+			logger(LOG_ERR, "UDPSndBuf cannot be negative!");
+			return false;
+		}
+	}
+
 	if(get_config_string(lookup_config(config_tree, "AddressFamily"), &afname)) {
 		if(!strcasecmp(afname, "IPv4"))
 			addressfamily = AF_INET;

src/net_socket.c

@@ -44,6 +44,8 @@
 int addressfamily = AF_UNSPEC;
 int maxtimeout = 900;
 int seconds_till_retry = 5;
+int udp_rcvbuf = 0;
+int udp_sndbuf = 0;
 
 listen_socket_t listen_socket[MAXSOCKETS];
 int listen_sockets;
@@ -261,6 +263,12 @@ int setup_vpn_in_socket(const sockaddr_t *sa) {
 	option = 1;
 	setsockopt(nfd, SOL_SOCKET, SO_REUSEADDR, (void *)&option, sizeof(option));
 
+	if(udp_rcvbuf && setsockopt(nfd, SOL_SOCKET, SO_RCVBUF, (void *)&udp_rcvbuf, sizeof(udp_rcvbuf)))
+		logger(LOG_WARNING, "Can't set UDP SO_RCVBUF to %i: %s", option, strerror(errno));
+
+	if(udp_sndbuf && setsockopt(nfd, SOL_SOCKET, SO_SNDBUF, (void *)&udp_sndbuf, sizeof(udp_sndbuf)))
+		logger(LOG_WARNING, "Can't set UDP SO_SNDBUF to %i: %s", option, strerror(errno));
+
 #if defined(IPPROTO_IPV6) && defined(IPV6_V6ONLY)
 	if(sa->sa.sa_family == AF_INET6)
 		setsockopt(nfd, IPPROTO_IPV6, IPV6_V6ONLY, (void *)&option, sizeof option);