linux-kernel - Re: [PATCH 1/3] pidns: fix vfork() after unshare(CLONE

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Date:	Thu, 22 Aug 2013 10:59:58 -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 1/3] pidns: fix vfork() after unshare(CLONE_NEWPID)

On Thu, Aug 22, 2013 at 10:09 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> 8382fcac "pidns: Outlaw thread creation after unshare(CLONE_NEWPID)"
> nacks CLONE_VM if the forking process unshared pid_ns, this obviously
> breaks vfork:
>
>         int main(void)
>         {
>                 assert(unshare(CLONE_NEWUSER | CLONE_NEWPID) == 0);
>                 assert(vfork() >= 0);
>                 _exit(0);
>                 return 0;
>         }
>
> fails without this patch.
>
> Change this check to use CLONE_SIGHAND instead. This also forbids
> CLONE_THREAD automatically, and this is what the comment implies.
>
> We could probably even drop CLONE_SIGHAND and use CLONE_THREAD,
> but it would be safer to not do this. The current check denies
> CLONE_SIGHAND implicitely and there is no reason to change this.

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

although...

>
> Reported-by: Colin Walters <walters@...hat.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/fork.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index e23bb19..86f5376 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1173,10 +1173,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>                 return ERR_PTR(-EINVAL);
>
>         /*
> -        * If the new process will be in a different pid namespace
> -        * don't allow the creation of threads.
> +        * If the new process will be in a different pid namespace don't
> +        * allow the creation of threads, or share the signal handlers.

...how about "If the new process will be in a different pid namespace,
don't allow it to share a thread group or signal handlers with the
parent"?

--Andy
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