Unix setuid demo

uid.c

#include <stdio.h>

int main() {
printf("real uid: %d\n", getuid());
printf("effective uid: %d\n", geteuid());

}

command:

MacBook-Pro:security w$ gcc -o uid uid.c

MacBook-Pro:security w$ ls -l uid

-rwxr-xr-x  1 w  staff  8784 Feb  7 17:37 uid

MacBook-Pro:security w$ ./uid

real uid: 501

effective uid: 501        still all 501

MacBook-Pro:security w$ sudo chown root ./uid

MacBook-Pro:security w$ ls -l uid

-rwxr-xr-x  1 root  staff  8784 Feb  7 17:37 uid         

MacBook-Pro:security w$ ./uid

real uid: 501

effective uid: 501

MacBook-Pro:security w$ chmod u+s ./uid

chmod: Unable to change file mode on ./uid: Operation not permitted

MacBook-Pro:security w$ sudo chmod u+s ./uid

MacBook-Pro:security w$ ls -l uid

-rwsr-xr-x  1 root  staff  8784 Feb  7 17:37 uid

MacBook-Pro:security w$ ./uid

real uid: 501

effective uid: 0

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