X-Git-Url: https://tinc-vpn.org/git/browse?a=blobdiff_plain;f=src%2Fnet_packet.c;h=8a5460cbad326ca170f583a63f47dd32eeecbcbf;hb=6779e381e59092b317a63356180db9a832ffb47d;hp=25d3efb861047cbea812a83f5b1f686224a577b0;hpb=9eb34ebfbe763e50b6efb1168dec52331559f7d1;p=tinc

diff --git a/src/net_packet.c b/src/net_packet.c
index 25d3efb8..8a5460cb 100644
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -1085,14 +1085,14 @@ static void try_sptps(node_t *n) {
 
 static void send_udp_probe_packet(node_t *n, int len) {
 	vpn_packet_t packet;
-	packet.offset = DEFAULT_PACKET_OFFSET;
-	memset(DATA(&packet), 0, 14);
 
 	if(len > sizeof(packet.data)) {
 		logger(DEBUG_TRAFFIC, LOG_INFO, "Truncating probe length %d to %s (%s)", len, n->name, n->hostname);
 		len = sizeof(packet.data);
 	}
 
+	packet.offset = DEFAULT_PACKET_OFFSET;
+	memset(DATA(&packet), 0, 14);
 	randomize(DATA(&packet) + 14, len - 14);
 	packet.len = len;
 	packet.priority = 0;
@@ -1333,14 +1333,19 @@ static void try_mtu(node_t *n) {
 			const length_t minmtu = MAX(n->minmtu, 512);
 			const float interval = n->maxmtu - minmtu;
 
-			/* The core of the discovery algorithm is this exponential.
-			   It produces very large probes early in the cycle, and then it very quickly decreases the probe size.
-			   This reflects the fact that in the most difficult cases, we don't get any feedback for probes that
-			   are too large, and therefore we need to concentrate on small offsets so that we can quickly converge
-			   on the precise MTU as we are approaching it.
-			   The last probe of the cycle is always 1 byte in size - this is to make sure we'll get at least one
-			   reply per cycle so that we can make progress. */
-			const length_t offset = powf(interval, multiplier * cycle_position / (probes_per_cycle - 1));
+			length_t offset = 0;
+
+			/* powf can be underflowed if n->maxmtu is less than 512 due to the minmtu MAX bound */
+			if(interval > 0) {
+				/* The core of the discovery algorithm is this exponential.
+				        It produces very large probes early in the cycle, and then it very quickly decreases the probe size.
+				        This reflects the fact that in the most difficult cases, we don't get any feedback for probes that
+				        are too large, and therefore we need to concentrate on small offsets so that we can quickly converge
+				        on the precise MTU as we are approaching it.
+				        The last probe of the cycle is always 1 byte in size - this is to make sure we'll get at least one
+				        reply per cycle so that we can make progress. */
+				offset = powf(interval, multiplier * cycle_position / (probes_per_cycle - 1));
+			}
 
 			length_t maxmtu = n->maxmtu;
 			send_udp_probe_packet(n, minmtu + offset);