Adding an IPv6 address to the interface USING libmnl and rtnetlink - linux

Question

I am trying to add an IPv6 address to an ethernet interface, using libmnl. After constructing a message and sending to the kernel, I saw that it was not added to the interface, even though the return codes for the kernel reply did not contain any error. Kindly can anybody have a look, and help me correct it. Am I supposed to add more attributes to the nlmsghdr or something else?
#include <assert.h>
#include <string.h>
#include <inttypes.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <libmnl/libmnl.h>
#include <linux/rtnetlink.h>
#include <net/if.h>
#include <time.h>
static struct mnl_socket *nl;
static unsigned int nlportid;
int mnl_init(void);
int mnl_init(){
nl = mnl_socket_open(NETLINK_ROUTE);
if(nl == NULL){
printf("Error: mnl_socket_open\n");
return 0;
}
if(mnl_socket_bind(nl, 0, MNL_SOCKET_AUTOPID) < 0){
printf("Error: mnl_socket_bind\n");
return 0;
}
nlportid = mnl_socket_get_portid(nl);
return 1;
}
int add_to_interface(const char* eip){
char buf[MNL_SOCKET_BUFFER_SIZE];
struct nlmsghdr *nlh;
struct ifaddrmsg *ifm;
int ret;
uint8_t seq;
nlh = mnl_nlmsg_put_header(buf);
nlh->nlmsg_type = RTM_NEWADDR;
nlh->nlmsg_flags = NLM_F_REQUEST|NLM_F_CREATE|NLM_F_EXCL;
nlh->nlmsg_seq = seq = time(NULL);
ifm = mnl_nlmsg_put_extra_header(nlh, sizeof(*ifm));
ifm->ifa_family = AF_INET6;
ifm->ifa_prefixlen = 64;
ifm->ifa_flags = IFA_F_PERMANENT;
ifm->ifa_scope = RT_SCOPE_UNIVERSE;
/* TODO get interaface name from user or configuration*/
ifm->ifa_index = if_nametoindex("eth0");
unsigned char eipn[16];
inet_pton(AF_INET6, eip, eipn);
mnl_attr_put(nlh, IFA_ADDRESS, 16,eipn);
mnl_nlmsg_fprintf(stdout, nlh, nlh->nlmsg_len, sizeof(struct ifaddrmsg));
if(mnl_socket_sendto(nl,nlh, nlh->nlmsg_len) < 0){
printf("Error: mnl_socket_sendto");
return 0;
}
ret = mnl_socket_recvfrom(nl,buf, sizeof(buf));
if(ret == -1){
printf("Error: mnl_socket_recvfrom");
return 0;
}
ret = mnl_cb_run(buf, ret, seq, nlportid, NULL, NULL);
return 0;
}
int main(int argc, char *argv[]){
if(mnl_init()){
add_to_interface("2001::20c:29ff:fe5f:13c7/64"); // for testing
}
}

Answer 1

I don't really know anything about libmnl, and the following solution is not perfect. But in case you're still stuck...
Notice that you're dropping several error codes. This one, in particular:
inet_pton(AF_INET6, eip, eipn);
Should be something in the lines of this:
ret = inet_pton(AF_INET6, eip, eipn);
if (ret != 1) {
printf("Bad address.\n");
return -22;
}
And I suppose you can tell where I'm going with this. This:
add_to_interface("2001::20c:29ff:fe5f:13c7/64"); // for testing
Should be this:
add_to_interface("2001::20c:29ff:fe5f:13c7"); // for testing
That fixes it for me. Except it hags at mnl_socket_recvfrom() because the kernel does not answer, apparently.
But do be more careful with those error codes; the ones I mentioned aren't the only ones.

Answer 2

Solution from Pablo Neira,
eipn should be 'struct in6_addr' instead.
mnl_attr_put(nlh, IFA_ADDRESS, 16,eipn);
So this looks like:
mnl_attr_put(nlh, IFA_ADDRESS, sizeof(eipn), &eipn);