How to run an exec() function as root and non-interactive?

Question

I am looking to fork() and exec with root privlages. It seems that privileges are not passed from the main thread once an exec function is called.

Now I have seen the post here that describes how to run a process as root, but when I try their solution..

char sudo[]="/usr/bin/sudo";
char pbin[]="/usr/local/bin/puppet";
execl(sudo,sudo,pbin,(char *)NULL);

The sudo command prompts for daemon's password. I am looking for non-interactive way to run the process as root. Is there anyway to do this short of removing Daemon's password?

Answer 1

To test the premise of your question that,

"It seems that privileges are not passed from the main thread once an exec function is called."

I wrote the following test code,

#include <unistd.h>
#include <stdio.h>
#include <errno.h>

int main() {
//    printf("starting");
    char sudo[]="/usr/bin/sudo";
    char pbin[]="mkdir";

//    printf("running test: %s %s",sudo,pbin);
    errno=0;

    if (fork() == 0) {
        int res = execl(sudo,sudo,pbin,"/bin/child",(char *)NULL);
//        printf("res:%d", res);
    }
    else {
        sleep(2);
        int res = execl(sudo,sudo,pbin,"/bin/parent",(char *)NULL);
//        printf("res:%d", res);
    }
}

And to my surprise, it worked without a problem, giving the following output:

$ sudo rm /bin/parent -rf ; sudo rm -rf /bin/child/
$ ls /bin/child/ -la
ls: cannot access '/bin/child/': No such file or directory
$ ls /bin/parent/ -la
ls: cannot access '/bin/parent/': No such file or directory

$ gcc main.c
$ sudo ./a.out

$ ls /bin/parent -la
total 8 drwxr-xr-x 2 root root 4096 Mar  6 11:42 . 
drwxr-xr-x 4 root root 4096 Mar  6 11:42 ..
$ ls /bin/child -la 
total 8 drwxr-xr-x 2 root root 4096 Mar  6 11:42 .
drwxr-xr-x 4 root root 4096 Mar  6 11:42 ..

As you can see there is a directory created by the parent process as well as the child process with root privileges.

---

Which got me thinking that your problem is in fact something else, as you state:

"The sudo command prompts for daemon's password. I am looking for non-interactive way to run the process as root. Is there anyway to do this short of removing Daemon's password?"

What you really want is a password-less sudo, which can be obtained by running

sudo visudo

and then adding the line:

ALL     ALL=(ALL) NOPASSWD: ALL

making your sudoers file looking like this.

#
# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/ instead of
# directly modifying this file.
#
# See the man page for details on how to write a sudoers file.
#
Defaults    env_reset
Defaults    mail_badpass
Defaults    secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin"

# Host alias specification

# User alias specification

# Cmnd alias specification

# User privilege specification
root    ALL=(ALL:ALL) ALL

# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

ALL ALL=(ALL) NOPASSWD: ALL
# See sudoers(5) for more information on "#include" directives:

#includedir /etc/sudoers.d