I am new in UNIX and new in Programming on it using C language.
What I want to do is the simple implementation for telnet
.
I made all required connection on both sides(Server & Client).
On the server: any request I receive, I fork
a new process to handle it
void createProcess() {
int pid = fork();
if( pid == CHILD ) {
transferHandling(s);
close(s);
_exit(0);
}
}
This method for handling commands that come from the client side:
int transferHandling(int socket) {
char buf[20];
char command[1024];
int n, pid, fd[2];
char *shell, *ps1;
if( checkLogin(socket) == 0 ) { // Used to check user account
send(socket, "Login Succeeded\n", 16, 0);
if( setupENV(info->name) == 0 ) { // setuid and setgid for the user
if( pipe(fd) == ERROR ) {
send(socket, "Server Busy\n", 12, 0);
return 1;
}
// Here I make a process to run the default shell for the user
// and make pipe between them
if((pid = fork()) > 0) {
dup2(fd[0], STDOUT_FILENO);
close(fd[1]);
//read commands from socket
while(1) {
n = recv(socket, command, 1024, 0);
// send the commands received to the child which contains the default shell
write(fd[0], command, n);
}
} else {
dup2(fd[1], STDIN_FILENO);
dup2(socket, STDOUT_FILENO);
dup2(socket, STDERR_FILENO);
close(fd[0]);
//run default shell
shell = getpwnam(info->name)->pw_shell;
execlp(shell, shell, NULL);
}
} else {
return 1; // setup ENV error
}
} else {
send(socket, "Login Failed\n", 13, 0);
}
}
This program runs successfully with any command, but when the client write any command like: wc, cd, bash (to run any other shell)
. The program is hanged.
This is the client side after the connection is setup.
if(login(soc)) { // send the user information for the server
char cmd[2024], cc[1024];
int n;
while(1) {
printf("Reading\n");
write(1, "username@hostname> ", 19);
n = read(0, cmd, 2024); // read the command from the STDIN, and send it to server
send(soc, cmd, n, 0);
printf("Receiving Now\n");
n = recv(soc, cmd, 2024, 0); // getting back the command output
write(1, cmd, n);
}
}