How to resolve the \'EINVAL\' error when entering the mount namespace in Go?

Entering the Mount Namespace in Go

Issue:

In Go, the setns call returns EINVAL (invalid argument) when attempting to enter the mount namespace for a container.

Explanation:

To enter a namespace using setns, the call must be made from a single-threaded context before the Go runtime threads start.

Solution:

There are two approaches to解决this issue:

1. Using Constructor Trick:

• Add the __attribute__((constructor)) macro to a C function that calls setns before Go starts.
• Modified Go code:

<code class="go">/*
#include <sched.h>
#include <stdio.h>
#include <fcntl.h>

__attribute__((constructor)) void enter_namespace(void) {
   setns(open("/proc/<PID>/ns/mnt", O_RDONLY, 0644), 0);
}
*/
import "C"</code>

2. Using syscall.RawSyscall:

• Ensure that the setns call is made in the main thread before starting the Go runtime threads.
• Use runtime.LockOSThread to lock the main thread if necessary.

<code class="go">package main

import (
    "fmt"
    "os"
    "path/filepath"
    "syscall"
    "runtime"
)

func main() {
    if syscall.Geteuid() != 0 {
        fmt.Println("abort: you want to run this as root")
        os.Exit(1)
    }

    if len(os.Args) != 2 {
        fmt.Println("abort: you must provide a PID as the sole argument")
        os.Exit(2)
    }

    // Lock the main thread to the OS thread
    runtime.LockOSThread()

    namespaces := []string{"ipc", "uts", "net", "pid", "mnt"}

    for i := range namespaces {
        fd, _ := syscall.Open(filepath.Join("/proc", os.Args[1], "ns", namespaces[i]), syscall.O_RDONLY, 0644)
        err, _, msg := syscall.RawSyscall(308, uintptr(fd), 0, 0) // 308 == setns

        if err != 0 {
            fmt.Println("setns on", namespaces[i], "namespace failed:", msg)
        } else {
            fmt.Println("setns on", namespaces[i], "namespace succeeded")
        }

    }
}</code>

Note:

• Make sure your kernel supports multiple namespaces by checking /proc/sys/kernel/namespaces_allowed.
• The kernel patch quoted in the documentation specifies that the process must have CAP_SYS_ADMIN in the target mount namespace. Ensure that these conditions are met before attempting to call setns.

The above is the detailed content of How to resolve the \'EINVAL\' error when entering the mount namespace in Go?. For more information, please follow other related articles on the PHP Chinese website!