linux-kernel - Re: [PATCH 2/3] pidns: kill the unnecessary CLONE_NEWPID in copy

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Date:	Thu, 22 Aug 2013 11:05:21 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brad Spengler <spender@...ecurity.net>,
	Colin Walters <walters@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] pidns: kill the unnecessary CLONE_NEWPID in copy_process()

On Thu, Aug 22, 2013 at 10:10 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> 8382fcac "pidns: Outlaw thread creation after unshare(CLONE_NEWPID)"
> nacks CLONE_NEWPID if the forking process unshared pid_ns. This is
> correct but unnecessary, copy_pid_ns() does the same check.
>
> Test-case (needs root or CLONE_NEWUSER should be added):
>
>         static int child(void *arg)
>         {
>                 return 0;
>         }
>
>         static char stack[16 * 1024];
>
>         int main(void)
>         {
>                 pid_t pid;
>
>                 assert(unshare(CLONE_NEWPID) == 0);
>
>                 pid = clone(child, stack + sizeof(stack) / 2,
>                                 CLONE_NEWPID | SIGCHLD, NULL);
>                 assert(pid < 0 && errno == EINVAL);
>
>                 return 0;
>         }
>
> clone(CLONE_NEWPID) correctly fails with or without this change.

Acked-by: Andy Lutomirski <luto@...capital.net>

>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/fork.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 86f5376..8d56338 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1176,7 +1176,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>          * If the new process will be in a different pid namespace don't
>          * allow the creation of threads, or share the signal handlers.
>          */
> -       if ((clone_flags & (CLONE_SIGHAND | CLONE_NEWPID)) &&
> +       if ((clone_flags & CLONE_SIGHAND) &&
>             (task_active_pid_ns(current) != current->nsproxy->pid_ns))
>                 return ERR_PTR(-EINVAL);
>
> --
> 1.5.5.1
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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