Add support for non-interactive shell to nasl_ssh_shell_open().

[jjnicola]

What:
Add support for non-interactive shell to nasl_ssh_shell_open().

Why:
Currently there are two options:

• an interactive shell with pty enabled, which responses are quite verbose (cmds, prompt, etc).
• one shot cmd exec which close the channel, with the response of the command only.

The new option allows to run multiple commands and only get the answer of this command, whitout the extra data like prompts and commands sent to the target.

How:

## This script uses a non-interactive (non pty) shell to elevate privileges
## in an ssh session.

include("ssh_func.inc");
include("misc_func.inc");

port = 22;
user = 'some_user';
pass = 'some_pass';
priv_pass = 'root_pass';

function clean_buffer(sess) {
  while( TRUE ) {
    c = ssh_shell_read(sess);
    if( strlen( c ) <= 0 ) break;
  }
};


#socket
soc = open_sock_tcp( port );
if( ! soc ) exit( 0 );
display (soc); 

#session
display("Open connection");
sess = ssh_connect( socket:soc );
display("User Auth");
prompt = ssh_userauth(sess, login:user, password:pass);

display("Open shell");
sess = ssh_shell_open (sess, pty:0);
sleep(2);
clean_buffer (sess);


cmd1 = "whoami" + '\n';
sh_wr = ssh_shell_write(sess, cmd:cmd1);
 
sleep(1);
ret = "";
while( TRUE ) {
   c = ssh_shell_read(sess);
   if( strlen( c ) <= 0 ) break;
   else {
     ret = ret + c;
     display("Return whoami before priv login: ", ret);
   }
}

display("Changing to root");
cmd1 = 'su -' + '\n';
sh_wr = ssh_shell_write(sess, cmd:cmd1);
 
sleep(2);
ret = "";
# This is optional, to print the promt and clean the buffer
while( TRUE ) {
   c = ssh_shell_read(sess);
   if( strlen( c ) <= 0 ) break;
   else {
   ret = ret + c;
   display(ret);
   }
}

if (strstr(ret, "Password")){
   cmd1 = priv_pass + '\n';
   sh_wr = ssh_shell_write(sess, cmd:cmd1);
   clean_buffer(sess);
}

cmd1 = "whoami" + '\n';
sh_wr = ssh_shell_write(sess, cmd:cmd1);
 
sleep(1);
ret = "";
while( TRUE ) {
   c = ssh_shell_read(sess);
   if( strlen( c ) <= 0 ) break;
   else {
     ret = ret + c;
     display("Return whoami after priv login: ", ret);
   }
}
 
ssh_shell_close(sess);
ssh_disconnect(sess);
display("Finished, close, disconnect script 1");

Checklist:

• Tests
• CHANGELOG Entry