1 files changed, 112 insertions, 0 deletions
diff --git a/sbin/natd/icmp.c b/sbin/natd/icmp.c
new file mode 100644
index 0000000..40464ff
--- /dev/null
+++ b/sbin/natd/icmp.c
@@ -0,0 +1,112 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <ctype.h>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <errno.h>
+#include <signal.h>
+
+#include <netdb.h>
+
+#include <netinet/in.h>
+#include <netinet/in_systm.h>
+#include <netinet/ip.h>
+#include <netinet/ip_icmp.h>
+#include <machine/in_cksum.h>
+
+#include <alias.h>
+
+#include "natd.h"
+
+int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
+{
+	char			icmpBuf[IP_MAXPACKET];
+	struct ip*		ip;
+	struct icmp*		icmp;
+	int			icmpLen;
+	int			failBytes;
+	int			failHdrLen;
+	struct sockaddr_in	addr;
+	int			wrote;
+	struct in_addr		swap;
+/*
+ * Don't send error if packet is
+ * not the first fragment.
+ */
+	if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
+		return 0;
+/*
+ * Dont respond if failed datagram is ICMP.
+ */
+	if (failedDgram->ip_p == IPPROTO_ICMP)
+		return 0;
+/*
+ * Start building the message.
+ */
+	ip   = (struct ip*) icmpBuf;
+	icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
+/*
+ * Complete ICMP part.
+ */
+	icmp->icmp_type  	= ICMP_UNREACH;
+	icmp->icmp_code		= ICMP_UNREACH_NEEDFRAG;
+	icmp->icmp_cksum	= 0;
+	icmp->icmp_void		= 0;
+	icmp->icmp_nextmtu	= htons (mtu);
+/*
+ * Copy header + 64 bits of original datagram.
+ */
+	failHdrLen = (failedDgram->ip_hl << 2);
+	failBytes  = failedDgram->ip_len - failHdrLen;
+	if (failBytes > 8)
+		failBytes = 8;
+
+	failBytes += failHdrLen;
+	icmpLen    = ICMP_MINLEN + failBytes;
+
+	memcpy (&icmp->icmp_ip, failedDgram, failBytes);
+/*
+ * Calculate checksum.
+ */
+	icmp->icmp_cksum = InternetChecksum ((u_short*) icmp, icmpLen);
+/*
+ * Add IP header using old IP header as template.
+ */
+	memcpy (ip, failedDgram, sizeof (struct ip));
+
+	ip->ip_v	= 4;
+	ip->ip_hl	= 5;
+	ip->ip_len	= htons (sizeof (struct ip) + icmpLen);
+	ip->ip_p	= IPPROTO_ICMP;
+	ip->ip_tos	= 0;
+
+	swap = ip->ip_dst;
+	ip->ip_dst = ip->ip_src;
+	ip->ip_src = swap;
+
+	PacketAliasIn ((char*) ip, IP_MAXPACKET);
+
+	addr.sin_family		= AF_INET;
+	addr.sin_addr		= ip->ip_dst;
+	addr.sin_port		= 0;
+/*
+ * Put packet into processing queue.
+ */
+	wrote = sendto (sock, 
+		        icmp,
+	    		icmpLen,
+	    		0,
+	    		(struct sockaddr*) &addr,
+	    		sizeof addr);
+	
+	if (wrote != icmpLen)
+		Warn ("Cannot send ICMP message.");
+
+	return 1;
+}
+
+