Develop Reference

How to connect android application to local domun

I am using esp32 to bring up a tcp server. In order not to access this server by ip, I use mDNS on the esp32 side. I can successfully contact the tcp server from the PC at esp32.local. Now I want to do the same from android application. I wrote a little c ++ code which I run on android.
int sockfd, connfd;
struct sockaddr_in servaddr, cli;
// socket create and varification
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1) {
hello ="socket creation failed...";
return env->NewStringUTF(hello.c_str());
}
else
hello="Socket successfully created..\n";
bzero(&servaddr, sizeof(servaddr));
// assign IP, PORT
servaddr.sin_family = AF_INET;
std::string url = "esp32.local";
servaddr.sin_addr.s_addr = inet_addr(url.c_str());
servaddr.sin_port = htons(1234);
struct hostent *result;
result = gethostbyname(url.c_str());
// destAddr.sin_addr.s_addr = ((in_addr*)hosten->h_addr_list[0])->s_addr;
if (!result)
{
hello ="gethostbyname...";
return env->NewStringUTF(hello.c_str());
}
// puts(result->h_name);
memmove(&(servaddr.sin_addr.s_addr), result->h_addr, result->h_length);
// connect the client socket to server socket
if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) != 0) {
hello="connection with the server failed..";
return env->NewStringUTF(hello.c_str());
}
else
printf("connected to the server..\n");
// function for chat
char buff = 0xA;
write(sockfd, &buff, sizeof(buff));
// close the socket
close(sockfd);
When trying to connect from android application, I get an error in function gethostbyname. . What do I need to do to access the .local domain?

std::string url = "esp32.local";
servaddr.sin_addr.s_addr = inet_addr(url.c_str());
inet_addr() does not support parsing hostnames like "sp32.local", only IP addresses. You need to use gethostbyname() or better getaddrinfo() instead.
struct hostent *result;
result = gethostbyname(url.c_str());
...
memmove(&(servaddr.sin_addr.s_addr), result->h_addr, result->h_length);
You are not copying the result of gethostbyname() into the sin_addr.s_addr correctly. Your commented-out code was doing it correctly:
servaddr.sin_addr.s_addr = ((in_addr*)(hosten->h_addr_list[0]))->s_addr;
Which can be simplified to:
servaddr.sin_addr = *(in_addr*)(hosten->h_addr_list[0]);
Or just:
servaddr.sin_addr = *(in_addr*)(hosten->h_addr);
But, getaddrinfo() would be easier to use than populating a sockaddr_in manually. And it supports IPv6, whereas gethostbyname() only supports IPv4:
std::string url = "esp32.local";
int sockfd = -1;
addrinfo hints = {};
addrinfo *result;
hints.ai_family = AF_INET; // AF_UNSPEC
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
// assign IP, PORT
int res = getaddrinfo(url.c_str(), "1234", &hints, &result);
if (res != 0) {
return env->NewStringUTF("getaddrinfo failed...");
}
for(addrinfo *addr = result; addr; addr = addr->ai_next) {
// socket create and varification
sockfd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
if (sockfd == -1) {
continue;
}
// connect the client socket to server socket
if (connect(sockfd, addr->ai_addr, addr->ai_addrlen) != 0) {
close(sockfd);
sockfd = -1;
continue;
}
break;
}
if (sockfd == -1) {
freeaddrinfo(result);
return env->NewStringUTF("socket creation/connect failed...");
}
freeaddrinfo(result);
printf("Connected to the server..\n");
// function for chat
char buff = 0xA;
write(sockfd, &buff, sizeof(buff));
// close the socket
close(sockfd);

Kernel (Android) to Userspace message multicast error: netlink_broadcast_filtered+0x24/0x3d4

I am trying to develop a function which would enable the Kernel (Android kernel: 4.9.59) to send a message to an/many userspace application and I have followed this example: Kernel to userspace application communication
However, when I am trying to call the message conveying function from the scheduler I am receiving the following error:
Fatal exception
PC is at netlink_broadcast_filtered+0x24/0x3d4
LR is at netlink_broadcast+0x14/0x20
Inside the kernel scheduler (kernel/sched) I have created a header (custom_code.h) which holds the function to send message from the kernel. I am not using Kernel module to inject this because Android does not support modules. The code inside custom_code.h is as follows:
#include <linux/sched.h>
#include <net/sock.h>
#include <linux/netlink.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#define MY_GROUP 1 //For netlink socket
struct sock* socket; //For netlink socket
struct sk_buff* socket_buff; //For netlink socket
static inline void nl_receive_callback (struct sk_buff *skb)
{
nlmsg_free(skb);
}
struct netlink_kernel_cfg cfg = {
.input = nl_receive_callback,
.groups = 1,
};
static inline int kernel_send_nl_msg(void)
{
struct nlmsghdr *nlsk_mh;
char* msg = "hello from kernel";
socket = netlink_kernel_create(&init_net, NETLINK_USERSOCK, &cfg);
socket_buff = nlmsg_new(256, GFP_KERNEL);
nlsk_mh = nlmsg_put(socket_buff, 0, 0, NLMSG_DONE, strlen(msg), 0);
//NETLINK_CB(socket_buff).pid = 0; // kernel pid pid is deprecated
NETLINK_CB(socket_buff).portid = 0;
NETLINK_CB(socket_buff).dst_group = MY_GROUP;
strcpy(nlmsg_data(nlsk_mh), msg);
nlmsg_multicast(socket, socket_buff, 0, MY_GROUP, GFP_KERNEL);
pr_info("%s", msg);//Print out the message to kernel
return 0;
}
I am calling the kernel_send_nl_msg from the sugov_start(struct cpufreq_policy *policy) function inside the cpufreq_schedutil.c (kernel/sched/cpufreq_schedutil.c), and I have built the whole kernel and flashed it on an Android device.
My modified code inside the kernel/sched/cpufreq_schedutil.c as follows:
static int sugov_start(struct cpufreq_policy *policy)
{
struct sugov_policy *sg_policy = policy->governor_data;
unsigned int cpu;
sg_policy->up_rate_delay_ns =
sg_policy->tunables->up_rate_limit_us * NSEC_PER_USEC;
sg_policy->down_rate_delay_ns =
sg_policy->tunables->down_rate_limit_us * NSEC_PER_USEC;
update_min_rate_limit_us(sg_policy);
sg_policy->last_freq_update_time = 0;
sg_policy->next_freq = UINT_MAX;
sg_policy->work_in_progress = false;
sg_policy->need_freq_update = false;
sg_policy->cached_raw_freq = 0;
for_each_cpu(cpu, policy->cpus) {
struct sugov_cpu *sg_cpu = &per_cpu(sugov_cpu, cpu);
memset(sg_cpu, 0, sizeof(*sg_cpu));
sg_cpu->sg_policy = sg_policy;
sg_cpu->flags = 0;
sugov_start_slack(cpu);
sg_cpu->iowait_boost_max = policy->cpuinfo.max_freq;
cpufreq_add_update_util_hook(cpu, &sg_cpu->update_util,
policy_is_shared(policy) ?
sugov_update_shared :
sugov_update_single);
}
if(kernel_send_nl_msg() != 0)
pr_info("Error sending message from Kernel using socket");
return 0;
}
After flashing the kernel image to the device and trying to boot the aformentioned error is conveyed by the device (even without booting).
My question on the error is as follows:
1) What might be the issue that is causing the error?
2) How can I send messages successfully from Android kernel to an/many userspace application? Any suggestion would be really helpful.

Kernel to userspace application communication

I am trying to make Kernel (Android, kernel 4.9.59) communicate with userspace applications. I found a solution using Netlink sockets: https://stackoverflow.com/a/25071310/4190159
The first issue with the solution is that struct netlink_skb_parms used in the solution does not have a member named 'pid', instead has a member named 'portid', which I believe is not the same as pid. Anyway, to compile my kernel side code/solution I used 'portid' member of struct netlink_skb_parms instead for initialization. However, now I am getting a different error.
My Kernel side Netlink socket code as follows:
#include <linux/sched.h>
//For netlink socket -->
#include <net/sock.h>
//#include <net/netlink.h>
#include <linux/netlink.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#define MY_GROUP 1 //For netlink socket
struct sock* socket; //For netlink socket
struct sk_buff* socket_buff; //For netlink socket
static void nl_receive_callback (struct sk_buff *skb)
{
nlmsg_free(skb);
}
static void kernel_send_nl_msg(void)
{
struct nlmsghdr *nlsk_mh;
char* msg = "hello from kernel";
socket = netlink_kernel_create(&init_net, NETLINK_USERSOCK, 1, nl_receive_callback, NULL, THIS_MODULE);
socket_buff = nlmsg_new(256, GFP_KERNEL);
nlsk_mh = nlmsg_put(socket_buff, 0, 0, NLMSG_DONE, strlen(msg), 0);
//NETLINK_CB(socket_buff).pid = 0; // kernel pid is deprecated
NETLINK_CB(socket_buff).portid = 0;
NETLINK_CB(socket_buff).dst_group = MY_GROUP;
strcpy(nlmsg_data(nlsk_mh), msg);
nlmsg_multicast(socket, socket_buff, 0, MY_GROUP, GFP_KERNEL);
pr_info("%s", msg);//Print out the message to kernel
return;
}
My userspace application side code to intercept the message from the kernel as follows:
#include <sys/socket.h>
#include <linux/netlink.h>
#define MY_GROUP 1
void user_recieve_nl_msg(void)
{
int sock_fd;
struct sockaddr_nl user_sockaddr;
struct nlmsghdr *nl_msghdr;
struct msghdr msghdr;
struct iovec iov;
char* kernel_msg;
sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USERSOCK);
memset(&user_sockaddr, 0, sizeof(user_sockaddr));
user_sockaddr.nl_family = AF_NETLINK;
user_sockaddr.nl_pid = getpid();
user_sockaddr.nl_groups = MY_GROUP;
bind(sock_fd, (struct sockaddr*)&user_sockaddr, sizeof(user_sockaddr));
while (1) {
nl_msghdr = (struct nlmsghdr*) malloc(NLMSG_SPACE(256));
memset(nl_msghdr, 0, NLMSG_SPACE(256));
iov.iov_base = (void*) nl_msghdr;
iov.iov_len = NLMSG_SPACE(256);
msghdr.msg_name = (void*) &user_sockaddr;
msghdr.msg_namelen = sizeof(user_sockaddr);
msghdr.msg_iov = &iov;
msghdr.msg_iovlen = 1;
recvmsg(sock_fd, &msghdr, 0);
kernel_msg = (char*)NLMSG_DATA(nl_msghdr);
print("Kernel message: %s\n", kernel_msg); // print to android logs
}
close(sock_fd);
}
When I am trying to build the android kernel I am receiving the fllowing error:
kernel/sched/custom_code.h:34:65: error: passing argument 3 of
'netlink_kernel_create' makes pointer from integer without a cast
[-Werror]
kernel/sched/custom_code.h:34:14: error: too many arguments to
function 'netlink_kernel_create'
Note the code for the Kernel side is written in custom_code.h.
My questions are as follows:
I have checked the function 'netlink_kernel_create' and I am sending the right number of arguments then why is the aformentioned error coming up? How this error could be resolved?
What should I do to establish a valid communication between the kernel and the userspace application so that messages could be passed (to and fro) between them?

1.
Let's check netlink_kernel_create function in linux kernel:
static inline struct sock *
netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)
{
return __netlink_kernel_create(net, unit, THIS_MODULE, cfg);
}
from here https://elixir.bootlin.com/linux/v4.9.59/source/include/linux/netlink.h#L60
Notice, that this function takes only 3 arguments ( instead of 6 in your code )
This function have been changed in kernel 3.6 ( from 6 parameters to 4 )
https://elixir.bootlin.com/linux/v3.6/source/include/linux/netlink.h#L185
And then renamed to __netlink_kernel_create in kernel 3.7
netlink_kernel_create function from 3.7 accepts 3 arguments
https://elixir.bootlin.com/linux/v3.7/source/include/linux/netlink.h#L48
Try change this
socket = netlink_kernel_create(&init_net, NETLINK_USERSOCK, 1, nl_receive_callback, NULL, THIS_MODULE);
to this
struct netlink_kernel_cfg cfg = {
.input = nl_receive_callback,
.groups = 1,
};
socket = netlink_kernel_create(&init_net, NETLINK_USERSOCK, &cfg);
Now you can send data in direction "kernel => application".
When you start your application, it will bind socket with user_sockaddr.nl_groups = MY_GROUP; bind(sock_fd, (struct sockaddr*)&user_sockaddr, sizeof(user_sockaddr));.
After this you can send data from kernel to application with NETLINK_CB(socket_buff).dst_group = MY_GROUP; nlmsg_multicast(socket, socket_buff, 0, MY_GROUP, GFP_KERNEL); and it will be received by application with recvmsg(sock_fd, &msghdr, 0);
How can I call kernel_send_nl_msg() function to actually communicate with the userspace?
You can call it from kernel module, which you write, compile and insmod into kernel. Or you can call it directly from kernel, but for this you will need to rebuild whole kernel.
If you want to send data in direction "application = > kernel", then you need to do things in reverse: bind new socket with another MY_GROUP2 in kernel and send data from application with nlmsg_multicast

Control a relay using an Android by Wi-Fi

How can I turn on or turn off a switch using Android and a Wi-Fi connection?
I have used SparkFuns IOIO to control relays. But how do I do it wirelessly?

I have a project just like this. Mine is sending position data for a steering system, but the idea is the same. I'll finish uploading it to Google Code soon. You can check it out at PowerWheelino.
The basic structure is this:
Touch event on Android sends data (over UDP) to the server.
The UDP server (WRT54G router in this case) receives the data and forwards it over serial to the Arduino.
The Arduino decides what to do with the data from the serial connection.
Keep in mind that the Arduino automatically resets when receiving data over serial (outside of the IDE Serial interface). See my post here on this topic and ways to get around it. Knowing this previously would have saved me a lot of troubleshooting.
Disclaimer:
This code requires some minor modification to accomplish what was requested by the OP. Since you've already made a working Android program with IOIO and an Arduino sketch, I assume this is within your abilities.
Here's the Android UDP client code:
Execute UdpClient::sendData() on touch event or button press.
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import android.util.Log;
public class UdpClient {
String messageStr;
DatagramSocket s;;
int server_port;
InetAddress local;
int msg_length;
byte[] message;
public UdpClient (String ipAddress, int port){
server_port = port;
try {
local = InetAddress.getByName(ipAddress);
s = new DatagramSocket();
}
catch (Exception e) {
e.printStackTrace();
Log.d("Powerwheelino",e.getStackTrace() + "error");
}
}
public boolean sendData(byte drive, byte steering){
byte drvByte = (byte) (drive & 0xFF);
byte steerByte = (byte) (steering & 0xFF);
message = new byte[2];
message[0] = drvByte;
message[1] = steerByte;
msg_length = message.length;
//message = messageStr.getBytes();
try {
DatagramPacket p = new DatagramPacket(message, msg_length,local,server_port);
s.send(p);
}
catch (Exception e) {
// TODO Auto-generated catch block
Log.d("Powerwheelino", e.getStackTrace() +"ERROR ");
e.printStackTrace();
return false;
}
return true;
}
}
Here's the listening UDP server (C++) code
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <string>
#include <SerialStream.h>
using namespace std;
class udp_server {
int sock;
int bytes_read;
socklen_t addr_len;
struct sockaddr_in server_addr , client_addr;
public:
udp_server(int portNum)
{
if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("Socket");
exit(1);
}
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(portNum);
server_addr.sin_addr.s_addr = INADDR_ANY;
bzero(&(server_addr.sin_zero),8);
if (bind(sock,(struct sockaddr *)&server_addr,
sizeof(struct sockaddr)) == -1)
{
perror("Bind");
exit(1);
}
addr_len = sizeof(struct sockaddr);
printf("\nUDPServer Waiting for client on port %d", portNum);
fflush(stdout);
}
int listen(char recv_data[]) {
while (1)
{
bytes_read = recvfrom(
sock,
recv_data,
1024,
0,
(struct sockaddr *)&client_addr,
&addr_len
);
recv_data[bytes_read] = '\0';
printf("\n(%s , %d) said : ",inet_ntoa(client_addr.sin_addr),
ntohs(client_addr.sin_port));
printf("%s", recv_data);
string drive;
string direction;
int speed, angle;
if ((recv_data[0] & 128) > 0) {
drive = "Fwd";
}
else {
drive = "Rev";
}
if ((recv_data[1] & 128) > 0) {
direction = "Left";
}
else {
direction = "Right";
}
speed = recv_data[0] & 127;
angle = recv_data[1] & 127;
printf("\t %s # %d and %s # %d",
drive.c_str(),
speed,
direction.c_str(),
angle);
fflush(stdout);
}
return 0;
}
};
Here's a snippet of the serial communication to the Arduino using LibSerial:
LibSerial::SerialStream myss;
SerialComm(int argc, char** argv) {
myss = new LibSerial::SerialStream("/dev/ttyS0", ios_base::out);
myss.SetBaudRate(LibSerial::SerialStreamBuf::BAUD_57600);
myss.SetCharSize(LibSerial::SerialStreamBuf::CHAR_SIZE_8);
myss.SetFlowControl(LibSerial::SerialStreamBuf::FLOW_CONTROL_NONE);
myss.SetParity(LibSerial::SerialStreamBuf::PARITY_NONE);
myss.SetNumOfStopBits(1);
const int Dsize = 2;
char buffer[1];
buffer[0] = 125; //0b00000001;
buffer[1] = '\0';
bitset(buffer[0]);
//myss << buffer;
myss.write(buffer,1);
//myss.Close();
}

You could use an Arduino with an Ethernet Shield - or possibly a Netduino. Basically, any device with wireless internet capabilities, since that is the only wireless protocol Android uses - besides Bluetooth (or NFC). When the user presses a button, you could open a Socket or a BluetoothSocket to communicate to the second device that it needs to open the switch. Fairly simple - if you have a wireless home network, then your device could be plugged in to your router with a physical wire - as long as your Android device and your microprocessor are on the same network. There might be other wireless options you could use - these are just the simplest I could thing of. Hope this helps!

That's why how I did it with my iPhone (should be the same on Android):
run a TCP server on a computer connected to the same network as your phone and by USB/serial to the Arduino.
This server should forward all incoming data coming through Wi-Fi from your Android phone through USB to the Arduino.
The phone should run a TCP client which sends a simple one-byte (maybe zero and non-zero) command
The Arduino shall be programmed so it listens for incoming serial data via interrupts; if a byte arrives it decides if it should switch the I/O pin on or off.

You can also use a Rugged Circuits Yellowjacket. It has a Wifi on board and can serve simple web pages and control inputs/outputs.

Trying to produce an exploitable Android Server

I'm trying to produce a simple server that will allow me test the Androids security features. I need to develop an application that will open a socket.
I've produced something similar in C, but I am having no look with java. Here's the application in C
// simpleserver3.c
#define MY_PORT 9999
#define MAXBUF 99
void indata(int clientfd, struct sockaddr_in client_addr)
{
char buffer[12];
printf("%s:%d connected\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
recv(clientfd, buffer, MAXBUF, 0); //this is will overflow the buffer
printf("%X \n", &buffer);
}
int main(int Count, char *Strings[])
{
struct sockaddr_in self, client_addr;
int sockfd,clientfd;
/*---Create streaming socket---*/
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 ) //socketfd = handle for socket
{
perror("Socket");
exit(errno);
}
/*---Initialize address/port structure---*/
bzero(&self, sizeof(self));
self.sin_family = AF_INET;
self.sin_port = htons(MY_PORT);
self.sin_addr.s_addr = INADDR_ANY;
/*---Bind the structure to the socket handle ---*/
if ( bind(sockfd, (struct sockaddr*)&self, sizeof(self)) != 0 )
{
perror("socket--bind");
exit(errno);
}
/*---Make it a "listening socket"---*/
if ( listen(sockfd, 20) != 0 )
{
perror("socket--listen");
exit(errno);
}
//set socklen_t to length of client address
socklen_t addrlen=sizeof(client_addr);
/*---accept a connection (creating a data pipe)---*/
clientfd = accept(sockfd, (struct sockaddr*)&client_addr, &addrlen); //create handle for communicating
indata(clientfd, client_addr);
close(clientfd);
close(sockfd);
return;
}
Any sugguestion would be great, Aneel

It's been a while since I used C, so I can't comment on your C code, but you should probably take a look at the Android documentation for the Socket class:
http://developer.android.com/reference/java/net/Socket.html

Check out this example: http://thinkandroid.wordpress.com/2010/03/27/incorporating-socket-programming-into-your-applications/