What is the best possible way to send packets coming on an interface back to the same interface without changing anything in the packet. I want to have a loopback effect for the actual traffic coming on one of my interfaces e.g eth0
I think you can easily achieve this with Python/Scapy. Something like
sniff(iface="eth0", prn=lambda x: sendp(x, iface="eth0"))
should do it.
I don't think you can do this easily with a physical interface. I used the tap module for this purpose, though. It's quite simple: I create a new tap interface, and my program writes back everything that is read from the device. I used this to test a proprietary network protocol - so it might or might not work for what you intend to do. The code is quite simple:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <linux/if_tun.h>
#define DEVNAME "gnlo0"
static int tun_alloc(char *dev)
{
struct ifreq ifr;
int fd, ret;
if ((fd = open("/dev/net/tun", O_RDWR)) < 0) {
perror("open");
return -1;
}
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP;
if (*dev)
strncpy(ifr.ifr_name, dev, IFNAMSIZ);
ret = ioctl(fd, TUNSETIFF, (void *)&ifr);
if (ret < 0) {
close(fd);
perror("ioctl TUNSETIFF");
return ret;
}
strcpy(dev, ifr.ifr_name);
return fd;
}
int main(int argc, char **argv)
{
int fd = -1;
int ret = 1;
char dev[IFNAMSIZ];
strncpy(dev, DEVNAME, IFNAMSIZ - 1);
printf("opening %s\n", dev);
fd = tun_alloc(dev);
if (fd < 0)
goto out;
char buf[512];
snprintf(buf, sizeof(buf) - 1,
"ip addr flush dev %s; ip link set dev %s up", dev, dev);
if (system(buf) < 0) {
perror("system");
goto out;
}
while (1) {
unsigned char packet[65535];
int len = read(fd, packet, sizeof(packet));
if (len < 0) {
perror("read");
goto out;
}
printf("incoming packet [%d octets]\n", len);
len = write(fd, packet, len);
printf("fed back packet [%d octets]\n", len);
}
ret = 0;
out:
if (fd >= 0)
close(fd);
return ret;
}
Related
Is it possible to change TCP congestion control algorithm from Cubic to Reno or vice versa using setsockopt call from C++ code in linux?
I am looking for an example code of doing so.
You can use the TCP_CONGESTION socket option to get or set the congestion control algorithm for a socket to one of the values listed in /proc/sys/net/ipv4/tcp_allowed_congestion_control or to any one of the values in /proc/sys/net/ipv4/tcp_available_congestion_control if your process is privileged.
C example:
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char **argv)
{
char buf[256];
socklen_t len;
int sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == -1)
{
perror("socket");
return -1;
}
len = sizeof(buf);
if (getsockopt(sock, IPPROTO_TCP, TCP_CONGESTION, buf, &len) != 0)
{
perror("getsockopt");
return -1;
}
printf("Current: %s\n", buf);
strcpy(buf, "reno");
len = strlen(buf);
if (setsockopt(sock, IPPROTO_TCP, TCP_CONGESTION, buf, len) != 0)
{
perror("setsockopt");
return -1;
}
len = sizeof(buf);
if (getsockopt(sock, IPPROTO_TCP, TCP_CONGESTION, buf, &len) != 0)
{
perror("getsockopt");
return -1;
}
printf("New: %s\n", buf);
close(sock);
return 0;
}
For me outputs:
Current: cubic
New: reno
I am doing some testing with Unix domain sockets and I can communicate over them without an issue, however, when I call accept() on the server side of my test program, the returned struct sockaddr_un doesn't contain a sun_path.
I am pretty sure that Inet sockets have their address and port properly filled out after an accept() call, so am I doing something wrong in my test program or am I expecting the wrong outcome?
I am running CentOS 6.2 and gcc 4.4.6.
Sample Code:
server.c
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define NAME "socket"
int main(int argc, char **argv)
{
int sock, msgsock, rval;
struct sockaddr_un server, client;
char buf[1024];
sock = socket(AF_UNIX, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
server.sun_family = AF_UNIX;
strcpy(server.sun_path, NAME);
if (bind(sock, (struct sockaddr *) &server, sizeof(struct sockaddr_un))) {
perror("binding stream socket");
exit(1);
}
printf("Socket has name %s\n", server.sun_path);
listen(sock, 5);
for (;;) {
socklen_t len = sizeof(client);
msgsock = accept(sock, (struct sockaddr *)&client, &len);
if (msgsock == -1)
perror("accept");
else do {
printf("strlen(sun_path) = %zu\n", strlen(client.sun_path));
bzero(buf, sizeof(buf));
if ((rval = read(msgsock, buf, 1024)) < 0)
perror("reading stream message");
else if (rval == 0)
printf("Ending connection\n");
else
printf("-->%s\n", buf);
} while (rval > 0);
close(msgsock);
}
close(sock);
unlink(NAME);
return 0;
}
client.c
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define DATA "Half a league, half a league . . ."
int main(int argc, char **argv)
{
int sock;
struct sockaddr_un server;
if (argc < 2) {
printf("usage:%s <pathname>", argv[0]);
exit(1);
}
sock = socket(AF_UNIX, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
server.sun_family = AF_UNIX;
strcpy(server.sun_path, argv[1]);
if (connect(sock, (struct sockaddr *) &server,
sizeof(struct sockaddr_un)) < 0) {
close(sock);
perror("connecting stream socket");
exit(1);
}
if (write(sock, DATA, sizeof(DATA)) < 0)
perror("writing on stream socket");
close(sock);
return 0;
}
Just to reiterate the question:
Why isn't sun_path filled out after the accept() call on the server?
I am really not sure if this is an answer at all. Probably it's more like musings about some research, though maybe still worth while reading.
The value filled by accept(2) seems to be quite protocol agnostic at least in Linux 3.16.0, NetBSD 6.1.4 and Darwin 13.1.0 kernels. In practice this means that the second parameter to accept(2), struct sockaddr * gets filled only up to what is shared between all protocols. So what you have in your hands after a successful acccept(2) is far from being a complete struct sockaddr_un.
Probably nobody thought it would be of much importance at the time first implementations of accept(2) were done and now we're stuck with this. Fortunately there is a way around that, in case one has lost the pathname used for socket with call to bind(2), and would now like to find it again.
With struct sockaddr_storage and getsockname(2) the member sun_path is accessible. So, to make sure you are getting all juicy details, call getsockname(2) after a successful call to accept(2) (this would be put after line number 40 in your server.c):
struct sockaddr_storage ss;
socklen_t sslen = sizeof(struct sockaddr_storage);
if (getsockname(msgsock, (struct sockaddr *)&ss, &sslen) == 0) {
struct sockaddr_un *un = (struct sockaddr_un *)&ss;
printf("socket name is: %s\n", un->sun_path);
}
Or just use this:
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define NAME "socket"
int main(int argc, char **argv)
{
int sock, msgsock, rval;
struct sockaddr_un server, client;
char buf[1024];
sock = socket(AF_UNIX, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
server.sun_family = AF_UNIX;
strcpy(server.sun_path, NAME);
if (bind(sock, (struct sockaddr *) &server, sizeof(struct sockaddr_un))) {
perror("binding stream socket");
exit(1);
}
printf("Socket has name %s\n", server.sun_path);
listen(sock, 5);
for (;;) {
socklen_t len = sizeof(client);
msgsock = accept(sock, (struct sockaddr *)&client, &len);
if (msgsock == -1)
perror("accept");
else do {
printf("strlen(sun_path) = %zu\n", strlen(client.sun_path));
struct sockaddr_storage ss;
socklen_t sslen = sizeof(struct sockaddr_storage);
if (getsockname(msgsock, (struct sockaddr *)&ss, &sslen) == 0) {
struct sockaddr_un *un = (struct sockaddr_un *)&ss;
printf("socket name is: %s\n", un->sun_path);
}
bzero(buf, sizeof(buf));
if ((rval = read(msgsock, buf, 1024)) < 0)
perror("reading stream message");
else if (rval == 0)
printf("Ending connection\n");
else
printf("-->%s\n", buf);
} while (rval > 0);
close(msgsock);
}
close(sock);
unlink(NAME);
return 0;
}
This has been tested, ie. it compiles and produces expected results, to work on a GNU/Linux system running kernel 3.16.0, a NetBSD system running 6.1.4 kernel, and a system equipped with OS/X Mavericks, running 13.1.0 kernel. In all of these behaviour of accept(2) is consistent: sun_path is nowhere to be found in the structure filled. The behaviour of getsockname(2) is consistent between different operating environments too, making all protocol specific details available.
You haven't bound your client socket to an address.
You don't need to bind your client socket to an address for connect() to work; but, if you expect to access your client address in your server, then you do have to bind().
Make sense?
Just setup a call to bind() before you connect in your client. Make sure you the path you use for you client is valid and check for errors as normal.
Hi am trying to implement net link user code and kernel code every thing works fine for unicast (src_addr.nl_groups = 0;). For mulicast, user code bind call always fails for non zero src_addr.nl_groups value. Really am not sure what value to put for multicast and how to proceed further. I checked the usage of netlink_broadcast in kernel source tree, so I put the same group Id value (RTMGRP_LINK) here. For unicast I found good number of help in internet but for multicast I don't think so . So Please help me to proceed further.
Error am getting is:
bind: No such file or directory
./a.out: can't bind socket (3)and err : -1: No such file or directory
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <stdio.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#define NETLINK_TEST 28
#define GROUP_IB 1
#define MAX_PAYLOAD 1024
struct sockaddr_nl src_addr, dst_addr;
struct nlmsghdr *nlh = NULL;
struct msghdr msg;
struct iovec iov;
int sock_fd;
int main(int argc, char ** argv)
{
int err;
sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
if (sock_fd<0) {
char s[BUFSIZ];
sprintf( s, "%s: can't assign fd for socket", argv[0] );
perror(s);
return -1;
}
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
src_addr.nl_groups = 0; // Unicast
//src_addr.nl_groups = RTMGRP_LINK; /* Multicast, bind call always fails for non zero values */
err = bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));
perror("bind");
if (err<0) {
char s[BUFSIZ];
sprintf( s, "%s: can't bind socket (%d)and err : %d", argv[0], sock_fd,err );
perror(s);
return -1;
}
memset(&dst_addr, 0, sizeof(dst_addr));
nlh = (struct nlhmsghdr *) malloc(NLMSG_SPACE(MAX_PAYLOAD));
memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
iov.iov_base = (void *)nlh;
iov.iov_len = NLMSG_SPACE(MAX_PAYLOAD);
msg.msg_name = (void *)&dst_addr;
msg.msg_namelen = sizeof(dst_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf("pid : %d\n Waiting for messages from kernel...\n",getpid());
recvmsg(sock_fd, &msg, 0);
printf("Message : %s\n", NLMSG_DATA(nlh));
close(sock_fd);
return 0;
}
Netlink socket binds are sensitive to what USER you are- I've seen them reliably fail if you are not running the program in question as 'root', at least on RedHat 6.
Try running as root 1st, before changing your logic. If you get the same failure as you do in normal operation, then you know it isn't (necessarily) a permissions issue.
The issue is
sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
Does you kernel module define the NETLINK_TEST family? your own family might must be supported at kernel module and it should post the message in the proper group using nlmsg_multicast()
RTMGRP_LINK is group defined in NETLINK_ROUTE.
This sample code is example for multicast
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <unistd.h>
#define MYPROTO NETLINK_USERSOCK
#define MYMGRP 21
int open_netlink(void)
{
int sock;
struct sockaddr_nl addr;
int group = MYMGRP;
sock = socket(AF_NETLINK, SOCK_RAW, MYPROTO);
if (sock < 0) {
printf("sock < 0.\n");
return sock;
}
memset((void *) &addr, 0, sizeof(addr));
addr.nl_family = AF_NETLINK;
addr.nl_pid = getpid();
/* addr.nl_groups = MYMGRP; */
if (bind(sock, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
printf("bind < 0.\n");
return -1;
}
if (setsockopt(sock, 270, NETLINK_ADD_MEMBERSHIP, &group, sizeof(group)) < 0) {
printf("setsockopt < 0\n");
return -1;
}
return sock;
}
void read_event(int sock)
{
struct sockaddr_nl nladdr;
struct msghdr msg;
struct iovec iov;
char buffer[65536];
int ret;
iov.iov_base = (void *) buffer;
iov.iov_len = sizeof(buffer);
msg.msg_name = (void *) &(nladdr);
msg.msg_namelen = sizeof(nladdr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf("Ok, listening.\n");
ret = recvmsg(sock, &msg, 0);
if (ret < 0)
printf("ret < 0.\n");
else
printf("Received message payload: %s\n", NLMSG_DATA((struct nlmsghdr *) &buffer));
}
int main(int argc, char *argv[])
{
int nls;
nls = open_netlink();
if (nls < 0)
return nls;
while (1)
read_event(nls);
return 0;
}
kernel module:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/netlink.h>
#include <net/netlink.h>
#include <net/net_namespace.h>
#define MYPROTO NETLINK_USERSOCK
#define MYGRP 21
static struct sock *nl_sk = NULL;
static void send_to_user(void)
{
struct sk_buff *skb;
struct nlmsghdr *nlh;
char *msg = "Hello from kernel";
int msg_size = strlen(msg) + 1;
int res;
pr_info("Creating skb.\n");
skb = nlmsg_new(NLMSG_ALIGN(msg_size + 1), GFP_KERNEL);
if (!skb) {
pr_err("Allocation failure.\n");
return;
}
nlh = nlmsg_put(skb, 0, 1, NLMSG_DONE, msg_size + 1, 0);
strcpy(nlmsg_data(nlh), msg);
pr_info("Sending skb.\n");
res = nlmsg_multicast(nl_sk, skb, 0, MYGRP, GFP_KERNEL);
if (res < 0)
pr_info("nlmsg_multicast() error: %d\n", res);
else
pr_info("Success.\n");
}
static int __init hello_init(void)
{
pr_info("Inserting hello module.\n");
nl_sk = netlink_kernel_create(&init_net, MYPROTO, NULL);
if (!nl_sk) {
pr_err("Error creating socket.\n");
return -10;
}
send_to_user();
netlink_kernel_release(nl_sk);
return 0;
}
static void __exit hello_exit(void)
{
pr_info("Exiting hello module.\n");
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");
We are trying to communicate with the server listening on Linux loopback interface via raw socket and it seems like the server does not get a single packet from us. The packets we send are visible in Wireshark.
Is raw socket on loopback possible at all? (Please, don't ask why we need it: it's too complicated to explain here)
EDIT: this is how we open it
_I_RawSocket = socket( PF_PACKET, SOCK_RAW, htons(ETH_P_ALL)))
memset( &ifr, 0, sizeof( ifr ) );
strcpy( ifr.ifr_ifrn.ifrn_name, _InterfaceName);
ioctl( _I_RawSocket, SIOCGIFINDEX, &ifr )
memset( &sll, 0, sizeof( sll ) );
sll.sll_family = AF_PACKET;
sll.sll_ifindex = ifr.ifr_ifindex;
sll.sll_protocol = htons( ETH_P_ALL );
bind( _I_RawSocket, (struct sockaddr *) &sll, sizeof( sll ))
The server is lighttpd and it's reachable via normal socket on localhost.
netstat --raw prints empty table but I'm absolutely sure we have two functional raw sockets on normal eth devices.
Raw sockets behave particularly fizzy with bind() and connect(), but I can't confirm that your issue lies with them. I suggest you follow a more straightforward approach:
Sender
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define DEST "127.0.0.1"
int main(int argc, char **argv)
{
int s;
struct sockaddr_in dst_addr;
char packet[50];
struct iphdr *ip = (struct iphdr *)packet;
if((s = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}
dst_addr.sin_family = AF_INET;
dst_addr.sin_port = 0; /* not needed in SOCK_RAW */
inet_pton(AF_INET, DEST, (struct in_addr *)&dst_addr.sin_addr.s_addr);
memset(dst_addr.sin_zero, 0, sizeof(dst_addr.sin_zero));
memset(packet, 'A', sizeof(packet)); /* payload will be all As */
ip->ihl = 5;
ip->version = 4;
ip->tos = 0;
ip->tot_len = htons(40);
ip->frag_off = 0; /* NF */
ip->ttl = 64;
ip->protocol = IPPROTO_RAW; /* this has to be IPPROTO_RAW */
ip->check = 0;
ip->saddr = dst_addr.sin_addr.s_addr;
ip->daddr = dst_addr.sin_addr.s_addr;
while(42) {
sleep(5);
if (sendto(s, packet, sizeof(packet), 0,
(struct sockaddr *)&dst_addr, (socklen_t)sizeof(dst_addr)) < 0)
perror("uh oh:");
}
return(0);
}
Receiver
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
int s;
struct sockaddr_in src_addr;
char packet[50];
if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0) {
perror("error:");
exit(EXIT_FAILURE);
}
memset(packet, 0, sizeof(packet));
socklen_t *len = (socklen_t *)sizeof(src_addr);
int fromlen = sizeof(src_addr);
while(42) {
if (recvfrom(s, &packet, sizeof(packet), 0,
(struct sockaddr *)&src_addr, &fromlen) < 0)
perror("uh oh:");
int i = sizeof(struct iphdr); /* print the payload */
for(; i < sizeof(packet); i++) {
printf("%c", packet[i]);
}
printf("\n");
}
return(0);
}
I hope these behave exactly like you want them to. Read man 7 raw for the gory details of why this works and more importantly man 7 packet if you want to extend it. Also, take note that IPPROTO_RAW implies the IP_HDRINCL socket option, which is why we're constructing the ip header ourselves - although the IP checksum and total length are computed and filled in by the kernel, still.
edit: In addition, if you wanted a raw socket with which to send valid data to an application like lighttpd, you'd have to match the protocol argument to socket() as well as provide valid values for the IP header fields. A proper ethernet header is not mandatory - the only important field will be filled for you by the kernel stack.
Please make sure bind to if_index
if (ioctl(sock, SIOCGIFINDEX, &stEthReq ) < 0 )
{
printf( "failed to get IF index!" );
return -1;
}
memset(&client_addr, 0, sizeof(client_addr));
client_addr.sll_family = AF_PACKET;
client_addr.sll_ifindex = stEthReq.ifr_ifru.ifru_ivalue;
client_addr.sll_protocol = VOS_HTONS(usEthType);
ret = bind(sock,(struct sockaddr *)(&client_addr), sizeof(client_addr));
How to UDP Broadcast with C in Linux?
In many IP stack, such as Linux, this code does not work. Your socket must have broadcast permissions. Try this:
bcast_sock = socket(AF_INET, SOCK_DGRAM, 0);
int broadcastEnable=1;
int ret=setsockopt(bcast_sock, SOL_SOCKET, SO_BROADCAST, &broadcastEnable, sizeof(broadcastEnable));
/* Add other code, sockaddr, sendto() etc. */
Unwind has it right, except you should use 'sendto'
Here is an example, that assumes you already have a socket. It was taken from clamav
static void
broadcast(const char *mess)
{
#define BROADCAST_PORT 30000u
struct sockaddr_in s;
int broadcastSock = socket(AF_INET, SOCK_DGRAM, 0);
if(broadcastSock < 0)
return;
memset(&s, '\0', sizeof(struct sockaddr_in));
s.sin_family = AF_INET;
s.sin_port = htons(BROADCAST_PORT)
s.sin_addr.s_addr = INADDR_BROADCAST; /* This is not correct : htonl(INADDR_BROADCAST); */
cli_dbgmsg("broadcast %s to %d\n", mess, broadcastSock);
if(sendto(broadcastSock, mess, strlen(mess), 0, (struct sockaddr *)&s, sizeof(struct sockaddr_in)) < 0)
perror("sendto");
}
Typically using the Berkeley sockets API, to sendto() one or more datagrams to a known broadcast-class IP address.
I wrote udp multicast server recently for testing. To subscribe to multicast you would subscribe your client to Multicast group 225.0.0.37 port 12346 and port 12345 (2 feeds - one feeds sends "Hello, World!" the other one "Bye, Office!").
I've been using it for testing my client, both client and server run on the same box so there might be bits that may not work but give it a try first.
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#define BYE_OFFICE 12346
#define HELLO_PORT 12345
#define HELLO_GROUP "225.0.0.37"
int main(int argc, char *argv[])
{
struct sockaddr_in addr;
struct sockaddr_in addr2;
int fd;
int fd2;
char *message = "Hello, World!";
char *message2 = "Bye, Office!";
if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket");
exit(1);
}
if ((fd2 = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket");
exit(1);
}
/* set up destination address */
memset(&addr,0,sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(HELLO_GROUP);
addr.sin_port=htons(HELLO_PORT);
memset(&addr2,0,sizeof(addr2));
addr2.sin_family = AF_INET;
addr2.sin_addr.s_addr = inet_addr(HELLO_GROUP);
addr2.sin_port=htons(BYE_OFFICE);
while (1)
{
if (sendto(fd, message, strlen(message), 0,(struct sockaddr *) &addr, sizeof(addr)) < 0)
{
perror("sendto");
exit(1);
}
sleep(3);
if (sendto(fd2, message2, strlen(message2), 0,(struct sockaddr *) &addr2, sizeof(addr2)) < 0)
{
perror("sendto2");
exit(1);
}
sleep(3);
}
}