linux-kernel - BUG: vfork() returns EINVAL after unshare(CLONE

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Message-ID: <CAEmTpZGJxtTuq8LDTLDK4V8to_Z30WEmo=p_2umboHvZaDr=Xg@mail.gmail.com>
Date:   Thu, 31 Mar 2022 13:36:42 +0500
From:   Марк Коренберг 
        <socketpair@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: BUG: vfork() returns EINVAL after unshare(CLONE_NEWTIME)

test:
----------------------------------------
#define _GNU_SOURCE 1
#include <stdio.h>
#include <sched.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <err.h>

#ifndef CLONE_NEWTIME
#define CLONE_NEWTIME   0x00000080
#endif

int main (void)
{
  if (unshare (CLONE_NEWTIME))  err (EXIT_FAILURE, "UNSHARE_NEWTIME");

  pid_t pid;
  switch (pid=vfork ())
  {
  case 0:
    _exit(0);
  case -1:
    err(EXIT_FAILURE, "vfork BUG");
  default:
    waitpid(pid, NULL, 0);
  }
  return 0;
}
-----------------------------------------------

Seems the bug in kernel/fork.c. It does not check for CLONE_VFORK

if (clone_flags & (CLONE_THREAD | CLONE_VM)) {
    if (nsp->time_ns != nsp->time_ns_for_children)
        return ERR_PTR(-EINVAL);
}

-----------------------------------
Changing vfork() to fork() in the program works ok.
The bug has been found during regression in our system because Python
3.10 runs subprocesses using vfork()+execve().

-- 
Segmentation fault