Fix PMTU discovery via datagram SPTPS.

[tinc] / src / net_packet.c

diff --git a/src/net_packet.c b/src/net_packet.c
index 012085e..ecdcfe2 100644 (file)
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -767,7 +767,7 @@ bool send_sptps_data(void *handle, uint8_t type, const char *data, size_t len) {
 
        /* Send it via TCP if it is a handshake packet, TCPOnly is in use, or this packet is larger than the MTU. */
 
-       if(type >= SPTPS_HANDSHAKE || ((myself->options | to->options) & OPTION_TCPONLY) || (type != PKT_PROBE && len > to->minmtu)) {
+       if(type >= SPTPS_HANDSHAKE || ((myself->options | to->options) & OPTION_TCPONLY) || (type != PKT_PROBE && (len - SPTPS_DATAGRAM_OVERHEAD) > to->minmtu)) {
                char buf[len * 4 / 3 + 5];
                b64encode(data, buf, len);
                /* If no valid key is known yet, send the packets using ANS_KEY requests,
@@ -792,6 +792,8 @@ bool send_sptps_data(void *handle, uint8_t type, const char *data, size_t len) {
 
        if(sendto(listen_socket[sock].udp.fd, data, len, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
                if(sockmsgsize(sockerrno)) {
+                       // Compensate for SPTPS overhead
+                       len -= SPTPS_DATAGRAM_OVERHEAD;
                        if(to->maxmtu >= len)
                                to->maxmtu = len - 1;
                        if(to->mtu >= len)