Setuid/Getuid in golang

Session

$ go build setuid.go
$ sudo su
[sudo] password for bore: 
# chown root:root setuid
# chmod u+s setuid
$ ./setuid
Real UID: 1000
Effective UID: 0
Real UID: 1000
Effective UID: 1000
$

// But if I use ps:

$ ps -eo euser,ruser,suser,comm | grep setuid
root     bore     root     setuid

// After seven seconds it's still the same, even if golang reports changed effective UID
$ ps -eo euser,ruser,suser,comm | grep setuid
root     bore     root     setuid

// C implementation behaves as expected
$ ps -eo euser,ruser,suser,comm | grep setuid
root     bore     root     setuid

$ ps -eo euser,ruser,suser,comm | grep setuid
bore     bore     bore     setuid

setuid.c

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

void printdelay()
{
    printf("Current UID: %ld\n", (long) getuid());
    printf("Effective UID: %ld\n", (long) geteuid());
    fflush(stdout);
    sleep(7);
}

int main(int argc, char *argv[])
{
    printdelay();

    if (setuid(getuid()) == -1) {
        printf("Error setting UID");
        exit(1);
    }
    
    printdelay();

    return 0;
}

setuid.go

package main

import (
        "fmt"
        "syscall"
        "time"
        "log"
        "os"
)

func main() {
    printdelay()

    err := syscall.Setuid(syscall.Getuid())
    if err != nil {
        log.Fatal(err)
        os.Exit(1)
    }
    
    printdelay()
}

func printdelay() {
    fmt.Printf("Real UID: %d\n", syscall.Getuid())
    fmt.Printf("Effective UID: %d\n", syscall.Geteuid())
    time.Sleep(7 * time.Second)
}

As noted in that bug. This is fixed in go 1.16.