I'm creating a C library that manage a lot of pheripherical of my embedded device. The S.O. used, is a linux dristro compiled with yocto. I'm trying to make some functions to connect my device to a wifi (well-know) router, with netlink (using the libnl commands). With the help of this community i've developed a function able to scan the routers in the area link here . Some of you know how to use the libnl command for connect my device to a router wifi?
I've developed the following code, that try to connect to an AP called "Validator_Test" (that have no password for authentication). The software return no error, but my device still remain disconneted from the ap.
static int iw_conn() {
struct nl_msg *msg = nlmsg_alloc();
int if_index = if_nametoindex("wlan0"); // Use this wireless interface for scanning.
// Open socket to kernel.
struct nl_sock *socket = nl_socket_alloc(); // Allocate new netlink socket in memory.
genl_connect(socket); // Create file descriptor and bind socket.
int driver_id = genl_ctrl_resolve(socket, "nl80211"); // Find the nl80211 driver ID.
genlmsg_put(msg, 0, 0, driver_id, 0, (NLM_F_REQUEST | NLM_F_ACK), NL80211_CMD_CONNECT, 0);
nla_put_u32(msg, NL80211_ATTR_IFINDEX, if_index); // Add message attribute, which interface to use.
nla_put(msg, NL80211_ATTR_SSID, strlen("Validator_Test"), "Validator_Test");
nla_put(msg, NL80211_ATTR_MAC, strlen("00:1e:42:21:e4:e9"), "00:1e:42:21:e4:e9");
int ret = nl_send_auto_complete(socket, msg); // Send the message.
printf("NL80211_CMD_CONNECT sent %d bytes to the kernel.\n", ret);
ret = nl_recvmsgs_default(socket); // Retrieve the kernel's answer. callback_dump() prints SSIDs to stdout.
nlmsg_free(msg);
if (ret < 0) {
printf("ERROR: nl_recvmsgs_default() returned %d (%s).\n", ret, nl_geterror(-ret));
return ret;
}
nla_put_failure:
return -ENOSPC;
}
It seems similar to this one:
How to use libnl and netlink socket for connect devices to AP programatically?
--
Thanks for the code.
Based on your code, I modified and did the test here; it works. The source code is at: https://github.com/neojou/nl80211/blob/master/test_connect/src/test_connect_nl80211.c
Some suggestions for this:
Make sure the test environment is correct
Before test the code, maybe you can try to use iw to do the test. iw is the open source tool, which uses netlink also. you can type "sudo iw wlan0 connect Validator_Test" and then use iwconfig to see if it is connected or not first. ( Suppose there is no security setting at the AP as you said )
there are two differences between your source code and mine
(1) don't need to set NL80211_ATTR_MAC
(2) ret = nl_recvmsgs_default(socket);
not sure if there is any judgement of the return value of your ap_conn(), but it seems better to return 0 in ap_conn(), when nl_recvmsgs_default() returns 0.
Related
I'm creating a C library that manages a lot of peripherical of my embedded device. The S.O. used, is a Linux distro compiled with yocto. I'm trying to make some functions to connect my device to wifi (well-know) router, with netlink (using the libnl commands). With the help of this community, I've developed a function able to scan the routers in the area. Some of you know how to use the libnl command to connecting my device to router wifi?
I've developed the following code, that tries to connect to an AP called "Validator_Test" (that have no authentication password). The software return no error, but my device still remain disconnected from the AP. Some of you know what is wrong in my code? Unfortunately, i've not found any example or documentation for this operation.
static int ap_conn() {
struct nl_msg *msg = nlmsg_alloc();
int if_index = if_nametoindex("wlan0"); // Use this wireless interface for scanning.
// Open socket to kernel.
struct nl_sock *socket = nl_socket_alloc(); // Allocate new netlink socket in memory.
genl_connect(socket); // Create file descriptor and bind socket.
int driver_id = genl_ctrl_resolve(socket, "nl80211"); // Find the nl80211 driver ID.
genlmsg_put(msg, 0, 0, driver_id, 0, (NLM_F_REQUEST | NLM_F_ACK), NL80211_CMD_CONNECT, 0);
nla_put_u32(msg, NL80211_ATTR_IFINDEX, if_index); // Add message attribute, which interface to use.
nla_put(msg, NL80211_ATTR_SSID, strlen("Validator_Test"), "Validator_Test");
nla_put(msg, NL80211_ATTR_MAC, strlen("00:1e:42:21:e4:e9"), "00:1e:42:21:e4:e9");
int ret = nl_send_auto_complete(socket, msg); // Send the message.
printf("NL80211_CMD_CONNECT sent %d bytes to the kernel.\n", ret);
ret = nl_recvmsgs_default(socket); // Retrieve the kernel's answer. callback_dump() prints SSIDs to stdout.
nlmsg_free(msg);
if (ret < 0) {
printf("ERROR: nl_recvmsgs_default() returned %d (%s).\n", ret, nl_geterror(-ret));
return ret;
}
nla_put_failure:
return -ENOSPC;
}
Thanks to all of you!
Thanks for the code.
Based on your code, I modified and did the test here; it works.
The source code is at:
https://github.com/neojou/nl80211/blob/master/test_connect/src/test_connect_nl80211.c
Some suggestions for this:
Make sure the test environment is correct
Before test the code, maybe you can try to use iw to do the test.
iw is the open source tool, which uses netlink also.
you can type "sudo iw wlan0 connect Validator_Test"
and then use iwconfig to see if it is connected or not first.
( Suppose there is no security setting at the AP as you said )
there are two differences between your source code and mine
(1) don't need to set NL80211_ATTR_MAC
(2) ret = nl_recvmsgs_default(socket);
not sure if there is any judgement of the return value of your ap_conn(),
but it seems better to return 0 in ap_conn(), when nl_recvmsgs_default() returns 0.
So how do you do this properly?
I know how to do it by creating socket, then setting IFF_PROMISC flag using ioctl (as explained in "howto check a network devices status in C?" and elsewhere), but this looks flawed at least in theory.
you read flags via ioctl
you update flags
someone else modified flags
you set updated flags via ioctl
Is there a better way or do I simply worry too much?
Later I found that one should add interface to PACKET_MR_PROMISC via setsockopt (which also does not have a race) like this:
void set_promisc(const char *ifname, bool enable)
{
struct packet_mreq mreq = {0};
int sfd;
int action;
if ((sfd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) == -1) {
perror("unable to open socket");
return;
}
mreq.mr_ifindex = if_nametoindex(ifname);
mreq.mr_type = PACKET_MR_PROMISC;
if (mreq.mr_ifindex == 0) {
perror("unable to get interface index");
return;
}
if (enable)
action = PACKET_ADD_MEMBERSHIP;
else
action = PACKET_DROP_MEMBERSHIP;
if (setsockopt(sfd, SOL_PACKET, action, &mreq, sizeof(mreq)) != 0) {
perror("unable to enter promiscouous mode");
return;
}
close(sfd);
}
Unfortunately this has no effect whatsoever on interface, although it should, if I unserstand the doc correctly. Possibly broken since 2001 (tm)?
Comments in pcap source also complain about this.
PACKET_MR_PROMISC turns on promiscuous mode for the device. That will not be reflected in the status shown by ifconfig as it does not modify the state of the global IFF_PROMISC flag on the device. That does not mean it hasn't been done though. This is how the pcap library works now and the fact that wireshark (and a dozen other utilities) can open a device and see packets not addressed to the local system shows that it works.
There is an internal counter on each device that is incremented each time a process uses PACKET_MR_PROMISC, and decremented when that process goes away. That solves the race you originally described.
From the last link you provided:
> IFF_PROMISC is not set,
It's not supposed to be set.
The correct way to put into promiscuous mode the device to which a
PF_PACKET socket is to do a SOL_PACKET/PACKET_ADD_MEMBERSHIP
"setsockopt()" call with PACKET_MR_PROMISC as the argument (see the
"packet(7)" man page), and that's what libpcap is doing.
The old way of directly setting IFF_PROMISC had problems - to quote the
comment at the front of "pcap-linux.c":
[snipped]
I have a bluetooth device which I can control using gatttool on linux. I want to develop my own c program that can send commands to it.
I have done bluetooth programming in the past and it is relatively straightforward, similar to network programming but this time, it is a bluetooth low energy device and following the principles here results in a host is down message when I can clearly connect/disconnect from it using gatttool.
How do I create this program? I know I should be using the bluez library but I am not sure where to start with Low energy devices.
int main(int argc, char **argv)
{
struct sockaddr_rc addr = { 0 };
int s, status;
char dest[18] = "B4:99:4C:5C:EE:49";
char buf[2048];
pthread_t rthread;
setbuf(stdout, NULL);
// allocate a socket
s = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
// set the connection parameters (who to connect to)
addr.rc_family = AF_BLUETOOTH;
addr.rc_channel = (uint8_t) 1;
str2ba( dest, &addr.rc_bdaddr );
// connect to server
status = connect(s, (struct sockaddr *)&addr, sizeof(addr));
if( status < 0 ){
perror("Error connecting to host\n");
exit(1);
}
while(fgets(buf, sizeof(buf), stdin) != NULL){
status = send(s, buf, sizeof(buf), 0);
if(status < 0){
printf("Error sending.\n");
exit(1);
}
}
close(s);
return;
I've been trying to figure out how to do this too: you may want to take a look at the source code in sandeepmistry/noble:src/l2cap-ble.c on Github. (The C component was factored out in this commit, so you need to look at older versions of the source.)
After building it (requires libbluetooth-dev) and running it, the l2cap-ble example essentially creates a simple TTY-like connection to the BLE device:
$ gcc -o l2cap-ble l2cap-ble.c utility.c -lbluetooth
$ ./l2cap-ble 12:34:56:78:9A:BC [public|random]
The source code illustrates a few BLE-specific functions (hci_*) that need to be interspersed with the standard socket I/O code.
UPDATE: I wrote a much more substantial and fully-functional program starting from this code: https://github.com/dlenski/ttblue. You can use this source code as an example of how to talk to a BLE gadget using Bluez.
your program is for classic bluetooth,to support my statement i would say ON any classic bluetooth device your code work would work fine
To get lescan i suggest to go though this link.sudo ./st would scan for nearby ble divices
https://github.com/carsonmcdonald/bluez-experiments
Another project on github.com looks clean: https://github.com/edrosten/libblepp
It's been mentioned in a discussion here: https://mbientlab.com/community/discussion/2492/bluetooth-le-library-linux
It's C++ not C though.
I'm working on a system that doesn't run unix / linux / windows or any familiar OS.
Yet, there are some libraries for sockets, one of them is socket.h.
The thing is that there is setsockopt function there, and some options, but there isn't fcntl.h library. I saw that this is the only way to get and set the socket's flags (O_NONBLOCK is what i seek).
Also, I saw that It is possible to use setsockopt with so_rcvtimeo and so_sndtimeo. I tried it and it is still blocking. The connect function was stuck when I was unplugging the ethernet cable right before the execution reached the connect line (in debug mode of course).
Is there a way to do it with the socket.h library only ?
Thanks,
Edit:
I'm using a system with Texas Instruments chip.
This is my current code, which doesn't work. "connect" returns -1 and I don't have errno to check what went wrong.
if (setsockopt(s, SOL_SOCKET, SO_BLOCKING, (char *)&isBlockingOption, sizeof(isBlockingOption)) < 0) {
/* closing the socket and exiting */
}
connect(s, &controlAddressStruct, sizeof(controlAddressStruct));
FD_ZERO(&conSocketSet);
FD_SET(s, &conSocketSet);
connectTimeout.tv_sec = 5;
connectTimeout.tv_usec = 0;
selectRet = fdselect( (int)s + 1, NULL, &conSocketSet, NULL, &connectTimeout);
if (selectRet == 1) {
socketLen = sizeof(so_error);
getsockopt(s, SOL_SOCKET, SO_ERROR, &so_error, &socketLen);
if (so_error == 0) {
return s;
}
}
return INVALID_SOCKET;
now, when the ethernet cable is plugged between the two systems, so_error = 0 and s is returned. Then when I read the FTP server reply, I get error so I exit the program.
But, if I removed the setsockopt for the SO_BLOCKING, everything is fine and the FTP server sends me the requested file.
If the send() and recv() interfaces are similar to the BSD sockets interface at all, the fourth parameter should correspond to flags. If so, you may be able to pass in MSG_DONTWAIT to the fourth parameter to effect non-blocking I/O.
I want to write a real-time analysis tool for wireless traffic.
Does anyone know how to read from a promiscuous (or sniffing) device in C?
I know that you need to have root access to do it. I was wondering if anyone knows what functions are necessary to do this. Normal sockets don't seem to make sense here.
On Linux you use a PF_PACKET socket to read data from a raw device, such as an ethernet interface running in promiscuous mode:
s = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))
This will send copies of every packet received up to your socket. It is quite likely that you don't really want every packet, though. The kernel can perform a first level of filtering using BPF, the Berkeley Packet Filter. BPF is essentially a stack-based virtual machine: it handles a small set of instructions such as:
ldh = load halfword (from packet)
jeq = jump if equal
ret = return with exit code
BPF's exit code tells the kernel whether to copy the packet to the socket or not. It is possible to write relatively small BPF programs directly, using setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, ). (WARNING: The kernel takes a struct sock_fprog, not a struct bpf_program, do not mix those up or your program will not work on some platforms).
For anything reasonably complex, you really want to use libpcap. BPF is limited in what it can do, in particular in the number of instructions it can execute per packet. libpcap will take care of splitting a complex filter up into two pieces, with the kernel performing a first level of filtering and the more-capable user-space code dropping the packets it didn't actually want to see.
libpcap also abstracts the kernel interface out of your application code. Linux and BSD use similar APIs, but Solaris requires DLPI and Windows uses something else.
I once had to listen on raw ethernet frames and ended up creating a wrapper for this. By calling the function with the device name, ex eth0 I got a socket in return that was in promiscuous mode.
What you need to do is to create a raw socket and then put it into promiscuous mode. Here is how I did it.
int raw_init (const char *device)
{
struct ifreq ifr;
int raw_socket;
memset (&ifr, 0, sizeof (struct ifreq));
/* Open A Raw Socket */
if ((raw_socket = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 1)
{
printf ("ERROR: Could not open socket, Got #?\n");
exit (1);
}
/* Set the device to use */
strcpy (ifr.ifr_name, device);
/* Get the current flags that the device might have */
if (ioctl (raw_socket, SIOCGIFFLAGS, &ifr) == -1)
{
perror ("Error: Could not retrive the flags from the device.\n");
exit (1);
}
/* Set the old flags plus the IFF_PROMISC flag */
ifr.ifr_flags |= IFF_PROMISC;
if (ioctl (raw_socket, SIOCSIFFLAGS, &ifr) == -1)
{
perror ("Error: Could not set flag IFF_PROMISC");
exit (1);
}
printf ("Entering promiscuous mode\n");
/* Configure the device */
if (ioctl (raw_socket, SIOCGIFINDEX, &ifr) < 0)
{
perror ("Error: Error getting the device index.\n");
exit (1);
}
return raw_socket;
}
Then when you have your socket you can just use select to handle packets as they arrive.
You could use the pcap library (see http://www.tcpdump.org/pcap.htm) which is also used by tcpdump and Wireshark.
Why wouldn't you use something like WireShark?
It is open source, so at least you could learn a few things from it if you don't want to just use it.
WireShark on linux has the capability to capture the PLCP (physical layer convergence protocol) header information.