Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand_struct

[Oleg Nesterov]

On 04/02, Eric W. Biederman wrote:
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1515,6 +1515,13 @@ static __latent_entropy struct task_struct 
> *copy_process(
>       if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
>               return ERR_PTR(-EINVAL);
>
> +     /* Disallow CLONE_THREAD with a shared SIGHAND structure.  No
> +      * one cares

Well, can't resists... I won't argue, but we can't know if no one cares
or not. I agree that most probably this won't break something, but who
knows... I am always scared when we add the incompatible changes.

> and supporting it leads to unnecessarily complex
> +      * code.
> +      */
> +     if ((clone_flags & CLONE_THREAD) && 
> (atomic_read(&current->sighand->count) > 1))
> +             return ERR_PTR(-EINVAL);

Perhaps the comment should explain why we do this and say that
sighand-unsharing in de_thread() depends on this.

Oleg.