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

From	ebiederm@xmission.com (Eric W. Biederman)
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand_struct
Date	2017-04-05 19:50 +0200
Message-ID	<tsXe9-5FW-9@gated-at.bofh.it> (permalink)
References	(6 earlier) <tqDtg-3qZ-17@gated-at.bofh.it> <trjC9-6Er-3@gated-at.bofh.it> <trWDv-6PH-3@gated-at.bofh.it> <trWDw-6PH-7@gated-at.bofh.it> <tsVYK-4Y7-27@gated-at.bofh.it>
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Oleg Nesterov <oleg@redhat.com> writes:

> 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.

I agree that changing userspace semantics is something to be very
careful with.  But at least for purposes of discussion I think this is a
good patch.

I can avoid this change but it requires moving sighand->siglock
into signal_struct and introducing a new spinlock into sighand_struct
to just guard the signal handlers.

However I think the change to move siglock would be a distraction from
the larger issues of this patchset.

Once we address the core issues I will be happy to revisit this.

>> 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.

That would be a better comment.

Eric

Thread

Re: [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped. ebiederm@xmission.com (Eric W. Biederman) - 2017-03-30 10:20 +0200
  [RFC][PATCH 0/2] exec: Fixing ptrace'd mulit-threaded hang ebiederm@xmission.com (Eric W. Biederman) - 2017-04-01 07:20 +0200
    [RFC][PATCH 1/2] sighand: Count each thread group once in sighand_struct ebiederm@xmission.com (Eric W. Biederman) - 2017-04-01 07:20 +0200
    [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped ebiederm@xmission.com (Eric W. Biederman) - 2017-04-01 07:30 +0200
      Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced  threads to be reaped Oleg Nesterov <oleg@redhat.com> - 2017-04-02 17:40 +0200
        Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped ebiederm@xmission.com (Eric W. Biederman) - 2017-04-02 21:00 +0200
          Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced  threads to be reaped Oleg Nesterov <oleg@redhat.com> - 2017-04-03 20:20 +0200
            Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 23:20 +0200
              Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced         threads to be reaped Oleg Nesterov <oleg@redhat.com> - 2017-04-05 18:50 +0200
    Re: [RFC][PATCH 0/2] exec: Fixing ptrace'd mulit-threaded hang Oleg Nesterov <oleg@redhat.com> - 2017-04-02 17:40 +0200
    [RFC][PATCH v2 4/5] exec: If possible don't wait for ptraced threads to be reaped ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 01:00 +0200
      Re: [RFC][PATCH v2 4/5] exec: If possible don't wait for ptraced         threads to be reaped Oleg Nesterov <oleg@redhat.com> - 2017-04-05 18:20 +0200
    [RFC][PATCH v2 1/5] ptrace: Don't wait in PTRACE_O_TRACEEXIT for exec or coredump ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 01:00 +0200
      Re: [RFC][PATCH v2 1/5] ptrace: Don't wait in PTRACE_O_TRACEEXIT         for exec or coredump Oleg Nesterov <oleg@redhat.com> - 2017-04-05 18:30 +0200
    [RFC][PATCH v2 0/5] exec: Fixing ptrace'd mulit-threaded hang ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 01:00 +0200
      [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand_struct ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 01:00 +0200
        Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a         shared sighand_struct Oleg Nesterov <oleg@redhat.com> - 2017-04-05 18:30 +0200
          Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand_struct ebiederm@xmission.com (Eric W. Biederman) - 2017-04-05 19:50 +0200
            Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a         shared sighand_struct Oleg Nesterov <oleg@redhat.com> - 2017-04-05 20:20 +0200
      [RFC][PATCH v2 2/5] sighand: Count each thread group once in sighand_struct ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 01:00 +0200
      [RFC][PATCH v2 5/5] signal: Don't allow accessing signal_struct by old threads after exec ebiederm@xmission.com (Eric W. Biederman) - 2017-04-03 01:10 +0200
        Re: [RFC][PATCH v2 5/5] signal: Don't allow accessing         signal_struct by old threads after exec Oleg Nesterov <oleg@redhat.com> - 2017-04-05 18:20 +0200
          Re: [RFC][PATCH v2 5/5] signal: Don't allow accessing signal_struct by old threads after exec ebiederm@xmission.com (Eric W. Biederman) - 2017-04-05 20:30 +0200
            Re: [RFC][PATCH v2 5/5] signal: Don't allow accessing signal_struct  by old threads after exec Oleg Nesterov <oleg@redhat.com> - 2017-04-06 18:00 +0200
  Re: [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped. Oleg Nesterov <oleg@redhat.com> - 2017-04-02 18:20 +0200
    Re: [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped. ebiederm@xmission.com (Eric W. Biederman) - 2017-04-02 23:20 +0200
      Re: [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped. Oleg Nesterov <oleg@redhat.com> - 2017-04-03 20:40 +0200
        scope of cred_guard_mutex. ebiederm@xmission.com (Eric W. Biederman) - 2017-04-04 01:00 +0200
          Re: scope of cred_guard_mutex. Oleg Nesterov <oleg@redhat.com> - 2017-04-05 18:10 +0200
            Re: scope of cred_guard_mutex. Kees Cook <keescook@chromium.org> - 2017-04-05 18:20 +0200
            Re: scope of cred_guard_mutex. ebiederm@xmission.com (Eric W. Biederman) - 2017-04-05 20:10 +0200
              Re: scope of cred_guard_mutex. Oleg Nesterov <oleg@redhat.com> - 2017-04-05 20:20 +0200
          Re: scope of cred_guard_mutex. Oleg Nesterov <oleg@redhat.com> - 2017-04-06 18:00 +0200
            Re: scope of cred_guard_mutex. Kees Cook <keescook@chromium.org> - 2017-04-08 00:10 +0200
        Re: [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped. ebiederm@xmission.com (Eric W. Biederman) - 2017-04-04 01:00 +0200

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