/*

 Example for process user-IDs

 Don't forget to make the resulting
 binary setuid by executing

   chmod u+s binaryname

 where 'binaryname' is the name of
 the binary produced by your compiler.

 To see something interesting, run
 the program from a user account
 different from the owner of the binary.

*/


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

#include <stdio.h>

#include <errno.h>
#include <pwd.h>


/* get real user-ID -- who's running us? */
void printruid(){

  uid_t uid;
  struct passwd *usrInfo;

  uid = getuid();

  usrInfo = getpwuid(uid);

  if (usrInfo != NULL) {
      printf("Real uid: %s\n", usrInfo->pw_name);
  }
}




/* get effective user-ID -- what privilege do we have? */
void printeuid(){
  uid_t uid;
  struct passwd *usrInfo;

  uid = geteuid();
  usrInfo = getpwuid(uid);

  if (usrInfo != NULL) {
      printf("Effective uid: %s\n", usrInfo->pw_name);
  }

}



int main(int argc, char **argv){

  int result;
  uid_t realuid, saveduid;

  realuid = getuid();
  saveduid = geteuid();

  printruid();
  printeuid();


  printf("\n");

  /* Change uid to real uid */

  if (seteuid(realuid) != -1) {
    printf("\nChanged euid to ruid\n");
  }
  else {
    printf("\nError when changing euid to ruid: %s\n", strerror(errno));
  }

  printruid();
  printeuid();


  printf("\n");

  /* Change uid to saved uid */

  if (seteuid(saveduid) != -1) {
    printf("\nChanged euid to saved uid\n");
  }
  else {
    printf("\nError when changing euid to saved uid: %s\n", strerror(errno));
  }

  printeuid();

  return 0;
}