Socket permissions ubuntu - c

Question

Hi I am new to Linux and have a project related to sockets. The problem I'm facing is that when I run the code with inputs eth0 for interface and ip address of my router i.e
./mycode eth0 192.168.1.1 it gives an error
You don't have permission to capture on that device (socket: Operation not permitted)
The code I took from a link is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pcap.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <net/ethernet.h>
#include <netinet/if_ether.h>
#include <sys/ioctl.h>
int main(int argc,const char* argv[]) {
// Get interface name and target IP address from command line.
if (argc<2) {
fprintf(stderr,"usage: send_arp <interface> <ipv4-address>\n");
exit(1);
}
const char* if_name=argv[1];
const char* target_ip_string=argv[2];
// Construct Ethernet header (except for source MAC address).
// (Destination set to broadcast address, FF:FF:FF:FF:FF:FF.)
struct ether_header header;
header.ether_type=htons(ETH_P_ARP);
memset(header.ether_dhost,0xff,sizeof(header.ether_dhost));
// Construct ARP request (except for MAC and IP addresses).
struct ether_arp req;
req.arp_hrd=htons(ARPHRD_ETHER);
req.arp_pro=htons(ETH_P_IP);
req.arp_hln=ETHER_ADDR_LEN;
req.arp_pln=sizeof(in_addr_t);
req.arp_op=htons(ARPOP_REQUEST);
memset(&req.arp_tha,0,sizeof(req.arp_tha));
// Convert target IP address from string, copy into ARP request.
struct in_addr target_ip_addr={0};
if (!inet_aton(target_ip_string,&target_ip_addr)) {
fprintf(stderr,"%s is not a valid IP address",target_ip_string);
exit(1);
}
memcpy(&req.arp_tpa,&target_ip_addr.s_addr,sizeof(req.arp_tpa));
// Write the interface name to an ifreq structure,
// for obtaining the source MAC and IP addresses.
struct ifreq ifr;
size_t if_name_len=strlen(if_name);
if (if_name_len<sizeof(ifr.ifr_name)) {
memcpy(ifr.ifr_name,if_name,if_name_len);
ifr.ifr_name[if_name_len]=0;
} else {
fprintf(stderr,"interface name is too long");
exit(1);
}
// Open an IPv4-family socket for use when calling ioctl.
int fd=socket(AF_INET,SOCK_DGRAM,0);
if (fd==-1) {
perror(0);
exit(1);
}
// Obtain the source IP address, copy into ARP request
if (ioctl(fd,SIOCGIFADDR,&ifr)==-1) {
perror(0);
close(fd);
exit(1);
}
struct sockaddr_in* source_ip_addr = (struct sockaddr_in*)&ifr.ifr_addr;
memcpy(&req.arp_spa,&source_ip_addr->sin_addr.s_addr,sizeof(req.arp_spa));
// Obtain the source MAC address, copy into Ethernet header and ARP request.
if (ioctl(fd,SIOCGIFHWADDR,&ifr)==-1) {
perror(0);
close(fd);
exit(1);
}
if (ifr.ifr_hwaddr.sa_family!=ARPHRD_ETHER) {
fprintf(stderr,"not an Ethernet interface");
close(fd);
exit(1);
}
const unsigned char* source_mac_addr=(unsigned char*)ifr.ifr_hwaddr.sa_data;
memcpy(header.ether_shost,source_mac_addr,sizeof(header.ether_shost));
memcpy(&req.arp_sha,source_mac_addr,sizeof(req.arp_sha));
close(fd);
// Combine the Ethernet header and ARP request into a contiguous block.
unsigned char frame[sizeof(struct ether_header)+sizeof(struct ether_arp)];
memcpy(frame,&header,sizeof(struct ether_header));
memcpy(frame+sizeof(struct ether_header),&req,sizeof(struct ether_arp));
// Open a PCAP packet capture descriptor for the specified interface.
char pcap_errbuf[PCAP_ERRBUF_SIZE];
pcap_errbuf[0]='\0';
pcap_t* pcap=pcap_open_live(if_name,96,0,0,pcap_errbuf);
if (pcap_errbuf[0]!='\0') {
fprintf(stderr,"%s\n",pcap_errbuf);
}
if (!pcap) {
exit(1);
}
// Write the Ethernet frame to the interface.
if (pcap_inject(pcap,frame,sizeof(frame))==-1) {
pcap_perror(pcap,0);
pcap_close(pcap);
exit(1);
}
// Close the PCAP descriptor.
pcap_close(pcap);
return 0;
}

Answer 1

You need root permissions to do that. Trying running your program as root.