No IP_ORIGDSTADDR header - linux-kernel

Question

I'm trying to get the original destination of UDP packet using IP_ORIGDSTADDR. On older kernel that mine, it seems to work (I'm running the currently debian testing kernel, 4.7.0-1-amd64).
#define _DEFAULT_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#define DEFAULT_ADDR "127.0.0.1"
#define DEFAULT_PORT 6666
int main(int ac, char **av)
{
int sock;
struct sockaddr_in sin;
memset(&sin, 0, sizeof sin);
sin.sin_family = AF_INET;
if (inet_aton(ac >= 2 ? av[1] : DEFAULT_ADDR, &sin.sin_addr) < 0) {
fprintf(stderr, "Invalid address\n");
goto err;
}
sin.sin_port = htons(ac >= 3 ? atoi(av[2]) : DEFAULT_PORT);
sock = socket(AF_INET, SOCK_DGRAM, 0);
if (sock < 0) {
perror("socket");
goto err;
}
if (bind(sock, (struct sockaddr *) &sin, sizeof sin) < 0) {
perror("bind");
goto close_err;
}
#define SOCK_OPT(l, n, v) do { \
int _v = v; \
socklen_t _s; \
if (setsockopt(sock, l, n, &_v, sizeof _v) < 0) { \
perror("setsockopt "# l "/" # n); \
goto close_err; \
} \
\
_s = sizeof (_v); \
if (getsockopt(sock, l, n, &_v, &_s) < 0) { \
perror("getsockopt "# l "/" # n); \
goto close_err; \
} \
\
if (_v != v) { \
fprintf(stderr, "Unexpected sockopt (expected %d, found %d)\n", v, _v); \
goto close_err; \
} \
\
printf(#l "/" #n " is set to %d\n", _v); \
\
} while (0)
SOCK_OPT(SOL_IP, IP_RECVORIGDSTADDR, 1);
SOCK_OPT(SOL_IP, IP_RECVOPTS, 1);
SOCK_OPT(SOL_IP, IP_PKTINFO, 1);
#undef SOCK_OPT
printf("Reading on %s:%d\n", inet_ntoa(sin.sin_addr), htons(sin.sin_port));
for (;;) {
ssize_t n;
char buf[1024];
char tmp[80];
struct iovec iovec[] = {
{
.iov_base = buf,
.iov_len = sizeof buf - 1,
}
};
struct msghdr msghdr;
struct cmsghdr *cmsg_ptr;
struct sockaddr_storage from = { 0 };
int port;
union cmsg_data {
struct sockaddr_in sin;
struct in_pktinfo pktinfo;
};
char msg_control[CMSG_SPACE(sizeof(union cmsg_data)) * 10] = { 0 };
int found;
memset(&msghdr, 0, sizeof msghdr);
msghdr.msg_name = &from;
msghdr.msg_namelen = sizeof from;
msghdr.msg_iov = iovec;
msghdr.msg_iovlen = sizeof iovec / sizeof iovec[0];
msghdr.msg_control = msg_control;
msghdr.msg_controllen = sizeof msg_control;
msghdr.msg_flags = MSG_EOR | MSG_TRUNC | MSG_CTRUNC | MSG_OOB | MSG_ERRQUEUE;
n = recvmsg(sock, &msghdr, MSG_OOB);
if (n < 0) {
perror("recvmsg");
continue;
}
if (buf[n - 1] == '\n')
n--;
buf[n] = 0;
switch (from.ss_family) {
default:
tmp[0] = 0;
break;
case AF_INET:
inet_ntop(AF_INET, &((struct sockaddr_in *) &from)->sin_addr, tmp, sizeof tmp);
port = htons(((struct sockaddr_in *) &from)->sin_port);
break;
case AF_INET6:
inet_ntop(AF_INET6, &((struct sockaddr_in6 *) &from)->sin6_addr, tmp, sizeof tmp);
port = htons(((struct sockaddr_in6 *) &from)->sin6_port);
break;
}
printf("%s:%d Rx %ldb: %.*s, msg_control = %zdb\n", tmp, port, n, (int) n, buf, sizeof msg_control);
found = 0;
for (cmsg_ptr = CMSG_FIRSTHDR(&msghdr); cmsg_ptr != NULL; cmsg_ptr = CMSG_NXTHDR(&msghdr, cmsg_ptr)) {
union cmsg_data *cmsg_data = (union cmsg_data *) CMSG_DATA(cmsg_ptr);
switch (cmsg_ptr->cmsg_level) {
default:
fprintf(stderr, "Unexecpted level : %d\n", cmsg_ptr->cmsg_level);
break;
case SOL_IP:
switch (cmsg_ptr->cmsg_type) {
default:
fprintf(stderr, "Unexecpted type : %d\n", cmsg_ptr->cmsg_type);
break;
case IP_ORIGDSTADDR:
printf("IP_ORIGDSTADDR: sin_addr = %s, sin_port = %d\n", inet_ntoa(cmsg_data->sin.sin_addr), htons(cmsg_data->sin.sin_port));
found++;
break;
case IP_PKTINFO:
snprintf(tmp, sizeof tmp, "%s", inet_ntoa(cmsg_data->pktinfo.ipi_spec_dst));
printf("IP_PKTINFO: ifindex = %u, spec_dst = %s, addr = %s\n", cmsg_data->pktinfo.ipi_ifindex, tmp, inet_ntoa(cmsg_data->pktinfo.ipi_addr));
break;
}
}
}
if (found != 1)
fprintf(stderr, "*** Warning: No SOL_IP / IP_ORIGDSTADDR found\n");
}
close_err:
close(sock);
err:
return 1;
}
When trying this bunch of code (eg. sending packets using netcat), I dont have any IP_ORIGDSTADDR, but only IP_PKTINFO : I need to have UDP port, only IP_ORIGDSTADDR can provide it.
Does anyone have met this strange behaviour ?