CODEWITHSUNDEEP
cctrlreverse-shell
BufferInterflow
BufferInterflow

Reputation: 1

Block SIGINT from terminating program

I need some help on C program - it is a reverse shell (https://github.com/arturgontijo/remoteShell/blob/master/reverseShell.c) I made few changes, like put that all in a loop and some sleep pattern + put some argument to pass directly IP and PORT now that thing works very good it's stable (problem that cannot autocomplete stuff with TAB I don't really care) BUT what I really care is that this thing will break if on target machine I press CTRL+C the program just exits itself. Now I used this example to block CTRL+C calls:

/* Signal Handler for SIGINT */
void sigintHandler(int sig_num) 
{ 
    /* Reset handler to catch SIGINT next time. 
       Refer http://en.cppreference.com/w/c/program/signal */
    signal(SIGINT, sigintHandler); 
    printf("\n Cannot be terminated using Ctrl+C \n"); 
    fflush(stdout); 
} 

signal(SIGINT, sigintHandler);

I got this example online and put it on my loop as well, but still from client pressing ctrl+C breaks program. I wonder dup2() is responsible for that or something because on simple C program this actually worked fine.

Upvotes: 0

Views: 2095

Answers (1)

Chris Frank
Chris Frank

Reputation: 4442

You can use the sigetops family of functions to manipulate the signals sent into your application.

So for your example you could use:

#include <signal.h>
#include <unistd.h>

int main(int argc, char **argv)
{
    sigset_t block_set;

    sigemptyset(&block_set);

    sigaddset(&block_set, SIGINT);

    sigprocmask(SIG_BLOCK, &block_set, NULL);

    while(1) {
        sleep(1);
    }
}

Running Example: https://repl.it/repls/RelevantImaginarySearchservice

You can unblock the signal at a later time by calling

sigprocmask(SIG_UNBLOCK, &block_set, NULL);

Upvotes: 1

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