RootExec: extremely dumb and insecure sudo replacement

rootexec.c

/* MIT License */

/* Copyright (c) 2016 Jajauma's GitHub */

/* Permission is hereby granted, free of charge, to any person obtaining a copy */
/* of this software and associated documentation files (the "Software"), to deal */
/* in the Software without restriction, including without limitation the rights */
/* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell */
/* copies of the Software, and to permit persons to whom the Software is */
/* furnished to do so, subject to the following conditions: */

/* The above copyright notice and this permission notice shall be included in all */
/* copies or substantial portions of the Software. */

/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR */
/* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, */
/* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE */
/* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER */
/* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, */
/* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE */
/* SOFTWARE. */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

/* # gcc -Wall -O2 -o RootExec rootexec.c */
/* # chown root RootExec */
/* # chmod u+s RootExec */

    int
main(int argc, char *argv[])
{
    if (argc < 2)
    {
        fprintf(stderr, "Usage: %s <command [args]>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    const char* this = argv[0];
    const char* program = argv[1];
    int narg = 1;
    for (; narg < argc; narg++)
    {
        argv[narg-1] = argv[narg];
    }
    argv[argc-1] = NULL;

    if (setreuid(0, -1) == -1)
    {
        perror("setreuid");
        fprintf(stderr,
                "\nNote that this program requires root ownership and set-user-ID \n"
                "mode to work, e.g. `chown root %s && chmod u+s %s'\n", this, this);
        exit(EXIT_FAILURE);
    }

    execvp(program, argv);
    perror("execvp");
    exit(EXIT_FAILURE);
}