setuid.c

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

int main(int argc,char **argv) {
	uid_t uid;
	char *end;
	int status;

	if (argc<3) {
		fprintf(stderr,"usage: %s uid cmd...\n",argv[0]);
		exit(1);
	}
	uid=strtoul(argv[1],&end,10);
	if (end==argv[1] || *end != '\0') {
		fprintf(stderr,"%s: %s: invalid uid\n",argv[0],argv[1]);
		exit(1);
	}
	status=setuid(uid);
	if (status==-1) {
		perror(argv[0]);
		exit(1);
	}

	status=execvp(argv[2],&argv[2]);
	if (status==-1) {
		perror(argv[0]);
		exit(1);
	}
	exit(0);
}