can't get setuid bit to work on Ubuntu 14.04

Question

I have a very simple program:

#define _GNU_SOURCE
#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>

void error(char *msg) {
  printf(msg);
  exit(-1);
}

int main(int argc, char **argv) {
    uid_t ruid, euid, suid;

    if (getresuid(&ruid, &euid, &suid) < 0)
        error("Error getting process uids");

    printf("%d %d %d\n", ruid, euid, suid);
}

Compiled as follows:

gcc -o print print.c

Its owned by root, and has the setuid bit set:

-rwsrwxr-x 1 root root 8648 Oct 8 20:10 ./print*

However when I run it, I get the following permissions:

1000 1000 1000

So both the real, effective, and saved set-uid permissions are all me (1000) and not root. Has anyone ran into this? any advice?

dimo dimo · Accepted Answer · 2014-10-09T18:39:39

Ok, figured it out. The issue was that the binary was living in on an encrypted file system. (moving it to /tmp for example fixes it). Its worth noting that in mount the encrypted file system doesn't show nosuid.

can't get setuid bit to work on Ubuntu 14.04

2 Answers