From e76468266a677537f1dbbe76e81aa87be60c67e3 Mon Sep 17 00:00:00 2001
From: Joel Grunbaum <joelgrun@gmail.com>
Date: Tue, 31 May 2022 09:40:08 +0000
Subject: [PATCH] Initial support for reachability
---
dns.c | 90 +++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 90 insertions(+), 0 deletions(-)
diff --git a/dns.c b/dns.c
index fb89c3a..3708389 100644
--- a/dns.c
+++ b/dns.c
@@ -1,4 +1,6 @@
#include <arpa/inet.h>
+#include <asm-generic/socket.h>
+#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -9,9 +11,12 @@
#include "dns.h"
#include <time.h>
#include <unistd.h>
+#include <errno.h>
void change_to_DNS_name_format(unsigned char* dns, unsigned char* host);
char* read_name(unsigned char* reader, unsigned char* buffer, int* count);
+void fill_ICMP_data(unsigned char* icmp_data, int datasize);
+unsigned short icmp_checksum(unsigned short* buf, int size);
// DNS code copied from
// https://gist.github.com/fffaraz/9d9170b57791c28ccda9255b48315168
@@ -64,6 +69,60 @@
char* rdata;
};
+#define ICMP_ECHO 8
+#define ICMP_ECHOREPLY 0
+
+struct ICMP_HEADER {
+ unsigned char type;
+ unsigned char code;
+ short checksum;
+ short id;
+ short seq;
+ long timestamp;
+};
+
+// Test if an IP address is hosting a DNS server
+int reachable(unsigned char* buf, char* dns_ip)
+{
+ int s, r;
+ int datasize = 64;
+ struct sockaddr_in dest;
+ struct timespec timeout;
+ timeout.tv_sec = 1;
+ timeout.tv_nsec = 0;
+
+ dest.sin_family = AF_INET;
+ dest.sin_port = htons(53);
+ dest.sin_addr.s_addr = inet_addr(dns_ip);
+
+ if (0) {
+ s = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
+ if (s < 0) {
+ printf("%d, %s\n", s, strerror(errno));
+ return -1;
+ }
+ setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(struct timespec));
+
+ fill_ICMP_data(buf, datasize);
+ ((struct ICMP_HEADER*)buf)->checksum = icmp_checksum((unsigned short*)buf, datasize);
+
+ r = sendto(s, buf, datasize, 0, (struct sockaddr*)&dest, sizeof(dest));
+ printf("%d\n", r);
+ }
+
+ s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+ if (s < 0) {
+ printf("%d, %s\n", s, strerror(errno));
+ return -1;
+ }
+ setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(struct timespec));
+
+ r = connect(s, (struct sockaddr*)&dest, sizeof(dest));
+ printf("%d", r);
+
+ return 1;
+}
+
// Test server dns_ip as IPv4 string for hostname
// Writes received packet to buf, which is supplied and returns time for request
struct timespec resolve(unsigned char* buf, char* hostname, char* dns_ip,
@@ -321,3 +380,34 @@
name[i - 1] = '\0';
return name;
}
+
+// Populate the sending ICMP packet with data
+void fill_ICMP_data(unsigned char* icmp_data, int datasize)
+{
+ struct ICMP_HEADER* h = (struct ICMP_HEADER*)icmp_data;
+ unsigned char* d = icmp_data + sizeof(struct ICMP_HEADER);
+
+ h->type = ICMP_ECHO;
+ h->code = 0;
+ h->id = getpid();
+ h->checksum = 0;
+ h->seq = 0;
+
+ memset(d, 'A', datasize - sizeof(struct ICMP_HEADER));
+}
+
+// Calculate the ICMP checksum
+unsigned short icmp_checksum(unsigned short* buf, int size)
+{
+ unsigned long checksum = 0;
+ while (size > 1) {
+ checksum += *buf++;
+ size -= sizeof(unsigned short);
+ }
+ if (size) {
+ checksum += *buf;
+ }
+ checksum = (checksum >> 16) + (checksum & 0xffff);
+ checksum += checksum >> 16;
+ return (unsigned short)~checksum;
+}
--
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