From: Guus Sliepen <guus@tinc-vpn.org>
Date: Fri, 1 Apr 2022 12:28:45 +0000 (+0200)
Subject: Prevent underflow when sending UDP probes.
X-Git-Url: https://tinc-vpn.org/git/browse?p=tinc;a=commitdiff_plain;h=ca7502b6de1e1ae49a62ad6b7a7ae8b760fa51ff

Prevent underflow when sending UDP probes.

Make sure send_udp_probe_packet() never tries to send a packet smaller
than MIN_PROBE_SIZE, otherwise length calculation could potentially wrap.

Fixes #351 on GitHub.
---

diff --git a/src/net_packet.c b/src/net_packet.c
index 2722fb23..5bdcb1aa 100644
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -1171,6 +1171,7 @@ static void send_udp_probe_packet(node_t *n, size_t len) {
 		len = sizeof(packet.data);
 	}
 
+	len = MAX(len, MIN_PROBE_SIZE);
 	packet.offset = DEFAULT_PACKET_OFFSET;
 	memset(DATA(&packet), 0, 14);
 	randomize(DATA(&packet) + 14, len - 14);