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Re: [PATCH v2] unshare: Unsharing a thread does not require unsharing a vm

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On 08/13, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > On 08/12, Eric W. Biederman wrote:
> >>
> >> +	if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
> >> +		if (atomic_read(&current->sighand->count) > 1)
> >> +			return -EINVAL;
> >> +	}
> >
> > I am still not sure we want this... please the the previous email.
>
> Reading your other email I did not see why you thought this check was
> unnecessary.
>
> > But perhaps I missed something.
>
> In short:
> clone(VM) --> mm_users > 1 && sighand_struct->count == 1
> followed by:
> unshare(SIGHAND)
> the unshare should succeed.
>
> Meanwhile:
> clone(VM|SIGHAND) --> mm_users > 1 && sighand_struct->count > 1
> followed by:
> unshare(SIGHAND)
> the unshare should fail.

Yes, yes, yes.

But once again, I meant we can remove this sighand->count check
if unshare(SIGHAND) checks current_is_single_threaded(). That is
why I suggested to do

	if (unshare_flags & CLONE_SIGHAND)
		unshare_flags |= CLONE_VM;

in sys_unshare(), or change check_unshare_flags() to check
"unshare_flags & (CLONE_VM | CLONE_SIGHAND)" before
current_is_single_threaded().



Damn. And this discussion makes me think that another cleanup makes
sense too. Can't we move all these unshare_flags manipulations into
check_unshare_flags? So that sys_unshare() will only do

	err = check_unshare_flags(&unshare_flags);

and the reader of this code won't need to read 2 functions to understand
whats going on.

Oleg.

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Re: [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov <oleg@redhat.com> - 2015-08-05 19:30 +0200
  Re: [PATCH] user_ns: use correct check for single-threadedness ebiederm@xmission.com (Eric W. Biederman) - 2015-08-05 20:10 +0200
    Re: [PATCH] user_ns: use correct check for single-threadedness ebiederm@xmission.com (Eric W. Biederman) - 2015-08-05 21:00 +0200
      Re: [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov <oleg@redhat.com> - 2015-08-06 16:10 +0200
        [PATCH 0/2] userns: Creation logic fixes ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 03:30 +0200
          [PATCH 2/2] userns,pidns: Force thread group sharing, not signal handler sharing ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 03:40 +0200
            Re: [PATCH 2/2] userns,pidns: Force thread group sharing, not  signal handler sharing Oleg Nesterov <oleg@redhat.com> - 2015-08-12 19:30 +0200
          [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 03:40 +0200
            Re: [PATCH 1/2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-12 20:00 +0200
              Re: [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 20:50 +0200
                Re: [PATCH 1/2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-13 15:00 +0200
                Re: [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-13 17:50 +0200
                Re: [PATCH 1/2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-13 18:20 +0200
                Re: [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-13 18:40 +0200
                Re: [PATCH 1/2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-13 19:00 +0200
                Re: [PATCH 1/2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-14 20:10 +0200
              [PATCH v2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 22:10 +0200
                Re: [PATCH v2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-13 15:00 +0200
                Re: [PATCH v2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-13 18:10 +0200
                Re: [PATCH v2] unshare: Unsharing a thread does not require  unsharing a vm Oleg Nesterov <oleg@redhat.com> - 2015-08-13 18:40 +0200
                Re: [PATCH v2] unshare: Unsharing a thread does not require unsharing a vm ebiederm@xmission.com (Eric W. Biederman) - 2015-08-13 18:50 +0200
          Re: [PATCH 0/2] userns: Creation logic fixes Kees Cook <keescook@chromium.org> - 2015-08-12 08:30 +0200
        Re: [PATCH] user_ns: use correct check for single-threadedness ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 03:30 +0200
          Re: [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov <oleg@redhat.com> - 2015-08-12 16:50 +0200
            Re: [PATCH] user_ns: use correct check for single-threadedness ebiederm@xmission.com (Eric W. Biederman) - 2015-08-12 17:20 +0200
      Re: [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov <oleg@redhat.com> - 2015-08-06 17:20 +0200
        Re: [PATCH] user_ns: use correct check for single-threadedness ebiederm@xmission.com (Eric W. Biederman) - 2015-08-06 23:30 +0200
      Re: [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov <oleg@redhat.com> - 2015-08-07 04:50 +0200

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