IPv6 address assignment & bind() issues

IPv6 address assignment & bind() issues

The C program given below assigns an IPv6 address to a specified network interface.

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>

#define IPV6_BINARY_LEN 128

int32_t set_ip_addr(const char *dev, const char *ip, int32_t prefix_len);

int main(int argc, char *argv[])
{
        struct sockaddr_in6 sa;
        int32_t size;
        int32_t sd;
        int32_t ret;

        if (argc != 4) {
                fprintf(stderr, "Usage: %s <dev> <ip address> <prefix Length>.\n",
                        argv[0]);
                goto out1;
        }

        ret = set_ip_addr(argv[1], argv[2], atoi(argv[3]));
        if (ret == -1) {
                fprintf(stderr, "Unable to set IP address.\n");
                goto out1;
        }

        sd = socket(AF_INET6, SOCK_DGRAM, 0);
        if (sd == -1) {
                perror("socket");
                goto out1;
        }

        memset(&sa, 0, sizeof(sa));
        sa.sin6_family = AF_INET6;
        sa.sin6_port = htons(49153);
        sa.sin6_scope_id = 0;
        ret = inet_pton(AF_INET6, argv[2], sa.sin6_addr.s6_addr);
        if (ret != 1) {
                perror("inet_pton");
                goto out2;
        }

        ret = bind(sd, (struct sockaddr *)&sa, sizeof(sa));
        if (ret == -1) {
                perror("bind");
                goto out2;
        }

        printf("Bind success!\n");

        close(sd);

        exit(0);
out2:
        close(sd);
out1:
        exit(1);
}

struct in6_ifreq {
        struct in6_addr ifr6_addr;
        uint32_t        ifr6_prefixlen;
        int32_t         ifr6_ifindex;
};

int32_t set_ip_addr(const char *dev, const char *ip, int32_t prefix_len)
{
        struct in6_ifreq in6_ifreq;
        struct ifreq ifreq;
        uint8_t ip_bin[IPV6_BINARY_LEN];
        int32_t sd;
        int32_t ret;

        if ((dev == NULL) || (ip == NULL) || (prefix_len < 0)) {
                fprintf(stderr, "%s: Invalid arguments.\n", __func__);
                goto out1;
        }

        ret = inet_pton(AF_INET6, ip, ip_bin);
        if (ret != 1) {
                perror("inet_pton");
                goto out1;
        }

        sd = socket(AF_INET6, SOCK_DGRAM, 0);
        if (sd == -1) {
                perror("socket");
                goto out1;
        }

        memset(&ifreq, 0, sizeof(ifreq));
        strncpy(ifreq.ifr_name, dev, IFNAMSIZ - 1);
        ret = ioctl(sd, SIOCGIFINDEX, &ifreq);
        if (ret == -1) {
                perror("ioctl");
                goto out2;
        }

        memset(&in6_ifreq, 0, sizeof(in6_ifreq));
        ret = inet_pton(AF_INET6, ip, &in6_ifreq.ifr6_addr.s6_addr);
        if (ret != 1) {
                perror("inet_pton");
                goto out2;
        }

        in6_ifreq.ifr6_ifindex = ifreq.ifr_ifindex;
        in6_ifreq.ifr6_prefixlen = prefix_len;

        ret = ioctl(sd, SIOCSIFADDR, &in6_ifreq);
        if (ret == -1) {
                perror("ioctl");
                goto out2;
        }

        close(sd);

        return 0;
out2:
        close(sd);
out1:
        return -1;
}

Compile and execute the program as shown below:

$ gcc -Wall set_ipv6_addr.c -oset_ipv6_addr
$ ./set_ipv6_addr eth0 2001:db8:0:145::243 64

The bind() system call in the above program fails and errno is set to EADDRNOTAVAIL.

To solve this issue (a workaround rather than a correct fix :-() follow the instructions given below:

1. Open the file net/ipv6/addrconf.c in the Linux kernel.
2. In the function ipv6_add_addr(), replace the following line

ifa->flags = flags | IFA_F_TENTATIVE;

with

ifa->flags = flags | IFA_F_NODAD;

Recompile the kernel and execute the previously listed program after booting into the new kernel.

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