Re: [PATCH 3/3] fork: unify and tighten up CLONE_NEWUSER/CLONE_NEWPID checks

[Andy Lutomirski]

On Thu, Aug 22, 2013 at 10:10 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> do_fork() denies CLONE_THREAD | CLONE_PARENT if NEWUSER | NEWPID.
>
> Then later copy_process() denies CLONE_SIGHAND if the new process
> will be in a different pid namespace (task_active_pid_ns() doesn't
> match current->nsproxy->pid_ns).
>
> This looks confusing and inconsistent. CLONE_NEWPID is very similar
> to the case when ->pid_ns was already unshared, we want the same
> restrictions so copy_process() should also nack CLONE_PARENT.
>
> And it would be better to deny CLONE_NEWUSER && CLONE_SIGHAND as
> well just for consistency.
>
> Kill the "CLONE_NEWUSER | CLONE_NEWPID" check in do_fork() and
> change copy_process() to the same check along with nsproxy->pid_ns
> we already have.

Did the old code actually prevent clone(CLONE_PARENT | CLONE_NEWPID)?
The new code explicitly does, and that looks like a good thing.

>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
>  kernel/fork.c |   22 ++++++++--------------
>  1 files changed, 8 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 8d56338..fae2ff7 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1173,12 +1173,15 @@ 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, or share the signal handlers.
> +        * If the new process will be in a different pid or user namespace
> +        * don't allow the creation of threads, or share the signal handlers,
> +        * or share the parent.
>          */
> -       if ((clone_flags & CLONE_SIGHAND) &&
> -           (task_active_pid_ns(current) != current->nsproxy->pid_ns))
> -               return ERR_PTR(-EINVAL);
> +       if (clone_flags & (CLONE_SIGHAND | CLONE_PARENT)) {
> +               if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
> +                   (task_active_pid_ns(current) != current->nsproxy->pid_ns))
> +                       return ERR_PTR(-EINVAL);
> +       }
>
>         retval = security_task_create(clone_flags);
>         if (retval)
> @@ -1575,15 +1578,6 @@ long do_fork(unsigned long clone_flags,
>         long nr;
>
>         /*
> -        * Do some preliminary argument and permissions checking before we
> -        * actually start allocating stuff
> -        */
> -       if (clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) {
> -               if (clone_flags & (CLONE_THREAD|CLONE_PARENT))
> -                       return -EINVAL;
> -       }
> -
> -       /*
>          * Determine whether and which event to report to ptracer.  When
>          * called from kernel_thread or CLONE_UNTRACED is explicitly
>          * requested, no event is reported; otherwise, report if the event
> --
> 1.5.5.1
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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