How to remove elevated privileges?

Hi,

I created a program that needs to be run as root or with `sudo`. In the program, I need to use `execv` to run another program, after forking a new process. I have the following:

Code:

---

// Fork the process.
    switch((pid = fork()))
    {
        case -1: // Error.
            fprintf(stderr, "%s: %s error: fork failed (%s)\n", program_name, __func__, strerror(errno));
            exit(EXIT_FAILURE);
        case 0: // Child.
// Remove root privileges.
            if(setuid(atoi(getenv("SUDO_UID"))) == -1)
            {
                fprintf(stderr, "%s: %s error: setuid failed (%s)\n", program_name, __func__, strerror(errno));
                exit(EXIT_FAILURE);
            }

// Proof the UID changed.
printf("2ID: %d\n", atoi(getenv("SUDO_UID")));

// Execute external program.
            if(execl(program, program, (char  *) NULL) == -1)
            {
                fprintf(stderr, "%s: %s error: execl failed (%s)\n", program_name, __func__, strerror(errno));
                exit(EXIT_FAILURE);
            }
    }

---

But the program that is executed lists a bunch of errors because it is not supposed to be run as root.

How can I execute an external program with the original users UID?

**EDIT:
Upon further investigation, it seems it is changing the UID to the original user. The problem seems to stem from the $HOME directory the external program tries to use for reading/writing files. It is trying to use the files under root instead of the user.

Looks like it was using $HOME which was set when sudo was used. The following fixed the problem:

Code:

---

// Get the users home directory.
    pw = getpwuid(atoi(getenv("SUDO_UID")));
// Change home directory back to the user and not root.
    setenv("HOME", pw->pw_dir, 1);

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