runtime: Process.Start() stuck forever on Alpine Linux when UserName is set in StartInfo

Code example:

using System;
using System.Diagnostics;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            var p = new Process
            {
                StartInfo = new ProcessStartInfo
                {
                    FileName = "/bin/sh",
                    UserName = "root",
                    RedirectStandardInput = true,
                    RedirectStandardOutput = true,
                    RedirectStandardError = true,
                    UseShellExecute = false
                },
                EnableRaisingEvents = true
            };

            Console.WriteLine("Trying to start /bin/sh");
            p.Start();
            Console.WriteLine("/bin/sh started successfully");
        }
    }
}

Publish the project with dotnet publish -c Release -r linux-musl-x64 --self-contained and copy the output to a fresh-installed Alpine Linux VM.

localhost:~/test# ./test
Trying to start /bin/sh

(output stuck here)

The process tree looks like this

localhost:~# cat /proc/2421/stack
[<0>] _do_fork+0x21c/0x2fe
[<0>] do_syscall_64+0x50/0xeb
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[<0>] 0xffffffffffffffff
localhost:~# cat /proc/2429/stack
[<0>] futex_wait_queue_me+0xbc/0x101
[<0>] futex_wait+0xd7/0x1f1
[<0>] do_futex+0x131/0x9a5
[<0>] __se_sys_futex+0x139/0x15e
[<0>] do_syscall_64+0x50/0xeb
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[<0>] 0xffffffffffffffff

It seems that the parent process already called vfork() but child has not yet exec or exit, leaving the parent in the uninterruptible sleep state. Related framework code could possibly be here

Environment info .NET Core SDK version: 3.0.100 OS: Alpine Linux 3.10 latest