Demonstrate poor setuid error checking

setuid-eagain.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

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

	if (!strcmp(argv[1], "alloc")) {
		int pid = 0;
			// fork children until RLIMIT_NPROC (hopefully)
		errno = -1;
		while (!(-1 == pid && EAGAIN == errno)) {
			pid = fork();
			if (!pid) { // child
				sleep(3600); // 1 hr
				exit(0);
			}
		}
		sleep(3600); // 1 hr
	} else if (!strcmp(argv[1], "setuid")) {
		if (argc < 3) return 1;
		int uid = atoi(argv[2]);
		if (setuid(uid)) perror("setuid");
		printf("getuid() = %d\n", getuid());
	} else {
		return 1;
	}

	return 0;
}