Checksum computation

src/Makefile.am

@@ -2,6 +2,7 @@ sbin_PROGRAMS = wrapsix-dnsproxy wrapsix-wrapper
 wrapsix_dnsproxy_SOURCES = dnsproxy.c
 wrapsix_wrapper_SOURCES = \
 			  arp.c arp.h \
+			  checksum.c checksum.h \
 			  ipv6.c ipv6.h \
 			  ipv4.h \
 			  nat.c nat.h \

src/checksum.c

@@ -0,0 +1,149 @@
+/*
+ *  WrapSix
+ *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as
+ *  published by the Free Software Foundation, either version 3 of the
+ *  License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <netinet/in.h>		/* htonl */
+#include <stdio.h>
+#include <stdlib.h>		/* malloc */
+#include <string.h>		/* memcpy */
+
+#include "checksum.h"
+#include "ipv4.h"
+#include "ipv6.h"
+
+/**
+ * General checksum computation function
+ *
+ * @param	data	Pointer to data of which to compute the checksum
+ * @param	length	Length of the data (in bytes)
+ *
+ * @return		Checksum
+ */
+unsigned short checksum(const void *data, int length)
+{
+	const unsigned short *buf = data;
+	unsigned int sum = 0;
+
+	while (length >= 2) {
+		sum += *buf++;
+
+		if (sum & 0x80000000) {
+			sum = (sum & 0xffff) + (sum >> 16);
+		}
+
+		length -= 2;
+	}
+
+	if (length) {
+		unsigned char temp[2];
+
+		temp[0] = *(unsigned char *) buf;
+		temp[1] = 0;
+
+		sum += *(unsigned short *) temp;
+	}
+
+	while (sum >> 16) {
+		sum = (sum & 0xffff) + (sum >> 16);
+	}
+
+	return ~sum;
+}
+
+/**
+ * IPv4 checksum computation function
+ *
+ * @param	ip_src	Source IPv4 address
+ * @param	ip_dest	Destination IPv4 address
+ * @param	length	Length of the payload (in bytes)
+ * @param	proto	Protocol in the payload
+ * @param	payload	Pointer to payload data
+ *
+ * @return		Checksum
+ */
+unsigned short checksum_ipv4(struct s_ipv4_addr ip_src,
+			     struct s_ipv4_addr ip_dest,
+			     unsigned short length, unsigned char proto,
+			     unsigned char *payload)
+{
+	unsigned char		*buffer;
+	struct s_ipv4_pseudo	*header;
+	unsigned short		 sum;
+
+	if ((buffer = malloc(sizeof(struct s_ipv4_pseudo) + length)) == NULL) {
+		fprintf(stderr, "[Error] Lack of free memory\n");
+		return 0;
+	}
+
+	header = (struct s_ipv4_pseudo *) buffer;
+
+	header->ip_src	= ip_src;
+	header->ip_dest = ip_dest;
+	header->zeros	= 0x0;
+	header->proto	= proto;
+	header->len	= htonl((unsigned int) length);
+
+	memcpy(buffer + sizeof(struct s_ipv4_pseudo), payload, (int) length);
+
+	sum = checksum(buffer, sizeof(struct s_ipv6_pseudo) + (int) length);
+
+	free(buffer);
+
+	return sum;
+}
+
+/**
+ * IPv6 checksum computation function
+ *
+ * @param	ip_src	Source IPv6 address
+ * @param	ip_dest	Destionation IPv6 address
+ * @param	length	Length of the payload (in bytes)
+ * @param	proto	Protocol in the payload
+ * @param	payload	Pointer to payload data
+ *
+ * @return		Checksum
+ */
+unsigned short checksum_ipv6(struct s_ipv6_addr ip_src,
+			     struct s_ipv6_addr ip_dest,
+			     unsigned short length, unsigned char proto,
+			     unsigned char *payload)
+{
+	unsigned char		*buffer;
+	struct s_ipv6_pseudo	*header;
+	unsigned short		 sum;
+
+	if ((buffer = malloc(sizeof(struct s_ipv6_pseudo) + length)) == NULL) {
+		fprintf(stderr, "[Error] Lack of free memory\n");
+		return 0;
+	}
+
+	header = (struct s_ipv6_pseudo *) buffer;
+
+	header->ip_src	    = ip_src;
+	header->ip_dest	    = ip_dest;
+	header->len	    = htonl((unsigned int) length);
+	header->zeros	    = 0x0;
+	header->next_header = proto;
+
+	memcpy(buffer + sizeof(struct s_ipv6_pseudo), payload, (int) length);
+
+	sum = checksum(buffer, sizeof(struct s_ipv6_pseudo) + (int) length);
+
+	free(buffer);
+
+	return sum;
+}

src/checksum.h

@@ -0,0 +1,33 @@
+/*
+ *  WrapSix
+ *  Copyright (C) 2008-2012  Michal Zima <xhire@mujmalysvet.cz>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as
+ *  published by the Free Software Foundation, either version 3 of the
+ *  License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef CHECKSUM_H
+#define CHECKSUM_H
+
+#include "ipv4.h"
+#include "ipv6.h"
+
+unsigned short checksum(const void *data, int length);
+unsigned short checksum_ipv4(struct s_ipv4_addr ip_src,
+			     struct s_ipv4_addr ip_dest, unsigned short length,
+			     unsigned char proto, unsigned char *payload);
+unsigned short checksum_ipv6(struct s_ipv6_addr ip_src,
+			     struct s_ipv6_addr ip_dest, unsigned short length,
+			     unsigned char proto, unsigned char *payload);
+
+#endif /* CHECKSUM_H */