/* chowntty.c - control ownership of your own tty

**

** v2 by Pegasus Epsilon <pegasus@pimpninjas.org>

** (C) 2013 Distribute Unmodified

** http://pegasus.pimpninjas.org/license

**

** rationale: if you're connected to it, it's yours, do what you want with it.

**

** known issues:

** you can use this to take ownership of /dev/tty and /dev/ptmx

** possibly other special "tty devices" as well. not sure how to stop this

** without making assumptions about the system.

**

** the redirected() function is my feeble attempt at avoiding this, but it

** still fails if you're clever.

*/

#define _XOPEN_SOURCE 500

/* >= 500, snprintf(), strdup(), readlink() */

#include <linux/limits.h> /* PATH_MAX */

#include <stdio.h> /* printf(), fileno(), puts(), snprintf() */

#include <string.h> /* strdup(), strcmp() */

#include <stdlib.h> /* exit(), free() */

#include <unistd.h> /* isatty(), ttyname(), chown(), readlink() */

#include <sys/types.h> /* getpwnam() */

#include <pwd.h> /* getpwnam() */

void usage (char *myself) {

printf("Usage: %s [LOGIN]\n", myself);

exit(-1);

}

int redirected (void) {

int i;

ssize_t len;

char link[PATH_MAX + 1], *last = NULL;

for (i = 0; i < 256; i++) {

snprintf(link, PATH_MAX + 1, "/proc/self/fd/%d", i);

len = readlink(link, link, PATH_MAX);

if (0 <= len) {

link[len] = 0;

if (!last) last = strdup(link);

else if (strcmp(last, link)) return 1;

}

}

if (last) free(last);

return 0;

}

int main (int argc, char **argv) {

struct passwd *pwd;

if (argc != 2 || NULL == (pwd = getpwnam(argv[1]))) usage(argv[0]);

if (isatty(fileno(stdin)) && !redirected())

chown(ttyname(fileno(stdin)), pwd->pw_uid, -1);

else puts("Nice try. No dice.");

return 0;

}