#define _POSIX_C_SOURCE 200809L

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

static void usage (void);
static int perm_set (uid_t);

int main (int argc, char *argv[])
{
	if (argc < 2) {
		usage();
		exit(1);
	}

	uid_t ruid = getuid();

	// Copy argv and argc
	int c_argc = argc - 1;
	char **c_argv = malloc((c_argc + 1) * sizeof(char *));
	if (!c_argv) {
		fprintf(stderr, "malloc: %s\n", strerror(errno));
		goto fail_end;
	}
	for (int i = 0; i < c_argc; i++)
		c_argv[i] = strdup(argv[i+1]);
	c_argc[c_argv] = NULL;

	if (perm_set(0) == -1) { // 0 = root
		fprintf(stderr, "perm_set: %s\n", strerror(errno));
		goto fail_end;
	}
	if (execvp(*c_argv, c_argv) == -1) // execvp searches in path
		fprintf(stderr, "execv: %s\n", strerror(errno));
	// if exec fails reset the permissions
	if (perm_set(ruid) == -1) { // 0 = root
		fprintf(stderr, "perm_set: %s\n", strerror(errno));
		goto fail_end;
	}

	fail_end:
	return 0;
}

static inline void usage (void)
{
	printf("usage: us [command]\n");
}

static inline int perm_set (uid_t id)
{
	return seteuid(id);	
}