rdo/rdo.c

#include <pwd.h>
#include <shadow.h>
#include <crypt.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <termios.h>

void getpwd(char* password){
	struct termios raw;
        tcgetattr(STDIN_FILENO, &raw);
        raw.c_lflag &= ~ECHO;
        tcsetattr(STDIN_FILENO, 0, &raw);
        
        printf("Password: ");
        fgets(password, 128, stdin);
        password[strcspn(password, "\n")] = 0;  
        
        raw.c_lflag |= ECHO;
        tcsetattr(STDIN_FILENO, 0, &raw);
        printf("\n");
}

void runprog(int argc, char** argv) {
        for(int i=0; i<argc; i++)
                argv[i] = argv[i + 1];
        setuid(0);
        setgid(0);
        if (execvp(argv[0], argv) != 0) perror(argv[0]);
}

int main(int argc, char** argv) {
	if (argc < 2) {
		fprintf(stderr, "Please specify a program to run.\n");
		return -1;
	}

	FILE* fp = fopen("/etc/rdo/username", "r");
	
	if (fp == NULL) {
		fprintf(stderr, "The file /etc/rdo/username could not be read.\n");
		return -2;
	}

	int ruid = getuid();
	if (ruid == 0) {
		fclose(fp);
                runprog(argc, argv);    
                return 0;
        }

	char username[64];
	fgets(username, 64, fp);
	fclose(fp);
	username[strcspn(username, "\n")] = 0;

	struct passwd* p = getpwnam(username);
	if (!p) {
		fprintf(stderr, "The user in the username file does not exist.\n");
		return -3;
	}

	int uid = p->pw_uid;
	if (uid != ruid && ruid != 0) {
		fprintf(stderr, "You are not in the username file.\n");
		return -4;
	}

	struct spwd* shadowEntry = getspnam(username);

	if (!shadowEntry) {
		fprintf(stderr, "Could not get shadow entry, suid bit not set or username invalid?\n");
		return -5;
	}

	int tries = 0;
	char password[128];
	while (tries < 3) {
		getpwd(password);	
		if (strcmp(shadowEntry->sp_pwdp, crypt(password, shadowEntry->sp_pwdp)) == 0) {
			runprog(argc, argv);    
                	return 0;		
		}
		fprintf(stderr, "Wrong password.\n");
		tries++;	
	}
        return -5;
}