Reacting to exceeded TTL/HL

src/icmp.c

@@ -353,3 +353,157 @@ int icmp_ndp(struct s_ethernet *ethq, struct s_ipv6 *ipq,
 
 	return 0;
 }
+
+/**
+ * Sends ICMPv4 error.
+ *
+ * @param	ip_dest	Destination IPv4 address
+ * @param	type	Type of ICMP error
+ * @param	code	Code of ICMP error
+ * @param	data	Original packet
+ * @param	length	Length of the original packet
+ *
+ * @return	0 for success
+ * @return	1 for failure
+ */
+int icmp4_error(struct s_ipv4_addr ip_dest, unsigned char type,
+		unsigned char code, unsigned char *data, unsigned short length)
+{
+	unsigned char *packet, *payload;
+	struct s_ipv4 *ip4;
+	struct s_icmp *icmp;
+
+	/* 4 = unused space after ICMP header */
+	unsigned short payload_size = length > 1500 - sizeof(struct s_ipv4) -
+					       sizeof(struct s_icmp) - 4 ?
+		1500 - sizeof(struct s_ipv4) - sizeof(struct s_icmp) - 4 :
+		length;
+
+	if ((packet = (unsigned char *) malloc(sizeof(struct s_ipv4) +
+	    sizeof(struct s_icmp) + 4 + payload_size)) == NULL) {
+		log_error("Lack of free memory");
+		return 1;
+	}
+
+	ip4 = (struct s_ipv4 *) packet;
+	icmp = (struct s_icmp *) (packet + sizeof(struct s_ipv4));
+	payload = (unsigned char *) (packet + sizeof(struct s_ipv4) +
+				     sizeof(struct s_icmp) + 4);
+
+	/* build IPv4 packet */
+	ip4->ver_hdrlen	  = 0x45;		/* ver 4, header length 20 B */
+	ip4->tos	  = 0x0;
+	ip4->len	  = htons(sizeof(struct s_ipv4) +
+				  sizeof(struct s_icmp) + 4 + payload_size);
+	ip4->id		  = 0x0;
+	ip4->flags_offset = htons(IPV4_FLAG_DONT_FRAGMENT);
+	ip4->ttl	  = 255;
+	ip4->proto	  = IPPROTO_ICMP;
+	ip4->ip_src	  = host_ipv4_addr;
+	ip4->ip_dest	  = ip_dest;
+
+	/* build ICMP header */
+	icmp->type = type;
+	icmp->code = code;
+	icmp->checksum = 0x0;
+
+	/* copy the payload data */
+	memcpy(payload, data, payload_size);
+
+	/* compute ICMP checksum */
+	icmp->checksum = checksum((unsigned char *) icmp,
+				  payload_size + 4 + sizeof(struct s_icmp));
+
+	/* compute IPv4 checksum */
+	ip4->checksum = checksum_ipv4(ip4->ip_src, ip4->ip_dest,
+				      htons(ip4->len), IPPROTO_ICMP,
+				      (unsigned char *) icmp);
+
+	/* send packet */
+	transmit_ipv4(&ip4->ip_dest, packet, htons(ip4->len));
+
+	/* clean-up */
+	free(packet);
+
+	return 0;
+}
+
+/**
+ * Sends ICMPv6 error.
+ *
+ * @param	mac_dest Destination MAC address
+ * @param	ip_dest	Destination IPv6 address
+ * @param	type	Type of ICMP error
+ * @param	code	Code of ICMP error
+ * @param	data	Original packet
+ * @param	length	Length of the original packet
+ *
+ * @return	0 for success
+ * @return	1 for failure
+ */
+int icmp6_error(struct s_mac_addr mac_dest, struct s_ipv6_addr ip_dest,
+		unsigned char type, unsigned char code, unsigned char *data,
+		unsigned short length)
+{
+	unsigned char *packet, *payload;
+	struct s_ethernet *eth;
+	struct s_ipv6 *ip6;
+	struct s_icmp *icmp;
+
+	/* 4 = unused space after ICMP header */
+	unsigned short payload_size = length > 1280 - sizeof(struct s_ipv6) -
+					       sizeof(struct s_icmp) - 4 ?
+		1280 - sizeof(struct s_ipv6) - sizeof(struct s_icmp) - 4 :
+		length;
+
+	if ((packet = (unsigned char *) malloc(sizeof(struct s_ethernet) +
+	    sizeof(struct s_ipv6) + sizeof(struct s_icmp) + 4 +
+	    payload_size)) == NULL) {
+		log_error("Lack of free memory");
+		return 1;
+	}
+
+	eth	= (struct s_ethernet *)	packet;
+	ip6	= (struct s_ipv6 *)	(packet + sizeof(struct s_ethernet));
+	icmp	= (struct s_icmp *)	(packet + sizeof(struct s_ethernet) +
+					 sizeof(struct s_ipv6));
+	payload	= (unsigned char *)	(packet + sizeof(struct s_ethernet) +
+					 sizeof(struct s_ipv6) +
+					 sizeof(struct s_icmp) + 4);
+
+	/* ethernet */
+	eth->dest = mac_dest;
+	eth->src  = mac;
+	eth->type = htons(ETHERTYPE_IPV6);
+
+	/* IPv6 */
+	ip6->ver	 = 0x60;
+	ip6->len	 = htons(sizeof(struct s_icmp) + 4 + payload_size);
+	ip6->next_header = IPPROTO_ICMPV6;
+	ip6->hop_limit	 = 255;
+	ip6->ip_src	 = host_ipv6_addr;
+	ip6->ip_dest	 = ip_dest;
+
+	/* ICMP */
+	icmp->type = type;
+	icmp->code = code;
+	icmp->checksum = 0x0;
+
+	/* copy the payload data */
+	memcpy(payload, data, payload_size);
+
+	/* compute ICMP checksum */
+	icmp->checksum = checksum_ipv6(host_ipv6_addr, ip_dest,
+				       sizeof(struct s_icmp) + 4 + payload_size,
+				       IPPROTO_ICMPV6,
+				       (unsigned char *) icmp);
+
+	/* send packet */
+	transmit_raw(packet, sizeof(struct s_ethernet) + sizeof(struct s_ipv6) +
+		     sizeof(struct s_icmp) + 4 + payload_size);
+
+	/* clean-up */
+	free(packet);
+
+	return 0;
+}

src/icmp.h

@@ -1,6 +1,6 @@
 /*
  *  WrapSix
- *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *  Copyright (C) 2008-2013  Michal Zima <xhire@mujmalysvet.cz>
  *
  *  This program is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -25,6 +25,7 @@
 /* ICMP types */
 #define ICMPV4_ECHO_REPLY	0x0
 #define ICMPV4_ECHO_REQUEST	0x8
+#define ICMPV4_TIME_EXCEEDED	0xb
 
 /* ICMPv6 types */
 #define ICMPV6_DST_UNREACHABLE	0x1
@@ -80,4 +81,10 @@ int icmp_ipv6(struct s_ethernet *eth, struct s_ipv6 *ip6, char *payload);
 int icmp_ndp(struct s_ethernet *ethq, struct s_ipv6 *ipq,
 	     struct s_icmp_ndp_ns *ndp_ns);
 
+int icmp4_error(struct s_ipv4_addr ip_dest, unsigned char type,
+		unsigned char code, unsigned char *data, unsigned short length);
+int icmp6_error(struct s_mac_addr mac_dest, struct s_ipv6_addr ip_dest,
+		unsigned char type, unsigned char code, unsigned char *data,
+		unsigned short length);
+
 #endif /* ICMP_H */

src/ipv4.c

@@ -1,6 +1,6 @@
 /*
  *  WrapSix
- *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *  Copyright (C) 2008-2013  Michal Zima <xhire@mujmalysvet.cz>
  *
  *  This program is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -55,6 +55,21 @@ int ipv4(struct s_ethernet *eth, char *packet)
 	data_size = htons(ip->len) - header_size;
 	payload = packet + header_size;
 
+	/* check and decrease TTL */
+	if (ip->ttl <= 1) {
+		/* deny this error for ICMP (except ping/pong)
+		 * and for non-first fragments */
+		if ((ip->proto != IPPROTO_ICMP || payload[0] & 0x0 ||
+		    payload[0] & 0x08) && !(ip->flags_offset & htons(0x1fff))) {
+			/* code 0 = ttl exceeded in transmit */
+			icmp4_error(ip->ip_src, ICMPV4_TIME_EXCEEDED, 0,
+				    (unsigned char *) packet, htons(ip->len));
+		}
+		return 1;
+	} else {
+		ip->ttl--;
+	}
+
 	switch (ip->proto) {
 		case IPPROTO_TCP:
 			log_debug("IPv4 Protocol: TCP");

src/ipv6.c

@@ -1,6 +1,6 @@
 /*
  *  WrapSix
- *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *  Copyright (C) 2008-2013  Michal Zima <xhire@mujmalysvet.cz>
  *
  *  This program is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -50,6 +50,20 @@ int ipv6(struct s_ethernet *eth, char *packet)
 		return 1;
 	}
 
+	/* check and decrease hop limit */
+	if (ip->hop_limit <= 1) {
+		/* deny this error for error ICMP messages */
+		if (ip->next_header != IPPROTO_ICMPV6 || payload[0] & 0x80) {
+			/* code 0 = hl exceeded in transmit */
+			icmp6_error(eth->src, ip->ip_src, ICMPV6_TIME_EXCEEDED,
+				    0, (unsigned char *) packet,
+				    htons(ip->len) + sizeof(struct s_ipv6));
+		}
+		return 1;
+	} else {
+		ip->hop_limit--;
+	}
+
 	switch (ip->next_header) {
 		case IPPROTO_TCP:
 			log_debug("IPv6 Protocol: TCP");

src/wrapper.c

@@ -41,6 +41,8 @@
 #define INTERFACE	"eth0"	/* be sure to turn off generic-segmentation-offload! */
 #define PREFIX		"64:ff9b::"
 #define IPV4_ADDR	"192.168.0.111"
+#define HOST_IPV6_ADDR	"fd77::1:0:1"
+#define HOST_IPV4_ADDR	"192.168.0.19"
 /* --- CONFIGURATION --- */
 
 
@@ -49,6 +51,8 @@ struct s_mac_addr	mac;
 struct s_ipv6_addr	ndp_multicast_addr;
 struct s_ipv6_addr	wrapsix_ipv6_prefix;
 struct s_ipv4_addr	wrapsix_ipv4_addr;
+struct s_ipv6_addr	host_ipv6_addr;
+struct s_ipv4_addr	host_ipv4_addr;
 
 int process(char *packet);
 
@@ -115,6 +119,12 @@ int main(int argc, char **argv)
 	/* compute binary IPv4 address of WrapSix */
 	inet_pton(AF_INET, IPV4_ADDR, &wrapsix_ipv4_addr);
 
+	/* compute binary IPv6 address of WrapSix host */
+	inet_pton(AF_INET6, HOST_IPV6_ADDR, &host_ipv6_addr);
+
+	/* compute binary IPv4 address of WrapSix host */
+	inet_pton(AF_INET, HOST_IPV4_ADDR, &host_ipv4_addr);
+
 	/* initiate sending socket */
 	if (transmission_init()) {
 		log_error("Unable to initiate sending socket");

src/wrapper.h

@@ -32,6 +32,8 @@ extern struct s_mac_addr	mac;
 extern struct s_ipv6_addr	ndp_multicast_addr;
 extern struct s_ipv6_addr	wrapsix_ipv6_prefix;
 extern struct s_ipv4_addr	wrapsix_ipv4_addr;
+extern struct s_ipv6_addr	host_ipv6_addr;
+extern struct s_ipv4_addr	host_ipv4_addr;
 
 void ipv6_to_ipv4(struct s_ipv6_addr *ipv6_addr, struct s_ipv4_addr *ipv4_addr);
 void ipv4_to_ipv6(struct s_ipv4_addr *ipv4_addr, struct s_ipv6_addr *ipv6_addr);