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From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: serge@hallyn.com, ebiederm@xmission.com, agruenba@redhat.com,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
	paul@paul-moore.com, viro@zeniv.linux.org.uk, avagin@openvz.org,
	linux-fsdevel@vger.kernel.org, mtk.manpages@gmail.com,
	akpm@linux-foundation.org, luto@amacapital.net,
	gorcunov@openvz.org, mingo@kernel.org, keescook@chromium.org
Subject: Re: [PATCH 2/2] pid_ns: Introduce ioctl to set vector of ns_last_pid's on ns hierarhy
Date: Thu, 27 Apr 2017 19:17:51 +0300	[thread overview]
Message-ID: <fdd61d9c-6f88-1669-4d12-31748395fe99@virtuozzo.com> (raw)
In-Reply-To: <20170427161255.GA19350@redhat.com>

On 27.04.2017 19:12, Oleg Nesterov wrote:
> On 04/26, Kirill Tkhai wrote:
>>
>> On 26.04.2017 18:53, Oleg Nesterov wrote:
>>>
>>>> +static long set_last_pid_vec(struct pid_namespace *pid_ns,
>>>> +			     struct pidns_ioc_req *req)
>>>> +{
>>>> +	char *str, *p;
>>>> +	int ret = 0;
>>>> +	pid_t pid;
>>>> +
>>>> +	read_lock(&tasklist_lock);
>>>> +	if (!pid_ns->child_reaper)
>>>> +		ret = -EINVAL;
>>>> +	read_unlock(&tasklist_lock);
>>>> +	if (ret)
>>>> +		return ret;
>>>
>>> why do you need to check ->child_reaper under tasklist_lock? this looks pointless.
>>>
>>> In fact I do not understand how it is possible to hit pid_ns->child_reaper == NULL,
>>> there must be at least one task in this namespace, otherwise you can't open a file
>>> which has f_op == ns_file_operations, no?
>>
>> Sure, it's impossible to pick a pid_ns, if there is no the pid_ns's tasks. I added
>> it under impression of
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=dfda351c729733a401981e8738ce497eaffcaa00
>> but here it's completely wrong. It will be removed in v2.
> 
> Hmm. But if I read this commit correctly then we really need to check
> pid_ns->child_reaper != NULL ?
> 
> Currently we can't pick an "empty" pid_ns. But after the commit above a task
> can do sys_unshare(CLONE_NEWPID), another (or the same) task can open its
> /proc/$pid/ns/pid_for_children and call ns_ioctl() before the 1st alloc_pid() ?

Another task can't open /proc/$pid/ns/pid_for_children before the 1st alloc_pid(),
because pid_for_children is available to open only after the 1st alloc_pid().
So, it's impossible to call ioctl() on it.
 
> Or I am totally confused?

  reply	other threads:[~2017-04-27 16:17 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-17 17:34 [PATCH 0/2] nsfs: Introduce ioctl to set vector of ns_last_pid's on pid ns hierarhy Kirill Tkhai
     [not found] ` <149245014695.17600.12640895883798122726.stgit-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2017-04-17 17:36   ` [PATCH 1/2] nsfs: Add namespace-specific ioctl (NS_SPECIFIC_IOC) Kirill Tkhai
2017-04-17 17:36 ` [PATCH 2/2] pid_ns: Introduce ioctl to set vector of ns_last_pid's on ns hierarhy Kirill Tkhai
     [not found]   ` <149245057248.17600.1341652606136269734.stgit-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2017-04-19 20:27     ` Serge E. Hallyn
2017-04-24 19:03     ` Cyrill Gorcunov
2017-04-26 15:53     ` Oleg Nesterov
     [not found]       ` <20170426155352.GA12131-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-04-26 16:11         ` Kirill Tkhai
     [not found]           ` <785e1986-da03-72aa-06c0-234ed2dbc0fd-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
2017-04-26 16:33             ` Kirill Tkhai
     [not found]               ` <005f52d9-efbe-9eaa-7f36-19945c8b06c3-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
2017-04-26 16:32                 ` Eric W. Biederman
     [not found]                   ` <87h91bcep5.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-04-26 16:43                     ` Kirill Tkhai
2017-04-26 17:01                       ` Eric W. Biederman
2017-04-27 16:12             ` Oleg Nesterov
2017-04-27 16:17               ` Kirill Tkhai [this message]
     [not found]                 ` <fdd61d9c-6f88-1669-4d12-31748395fe99-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
2017-04-27 16:22                   ` Oleg Nesterov
2017-04-28  9:17                     ` Kirill Tkhai
2017-05-02 16:33                       ` Oleg Nesterov
     [not found]                         ` <20170502163324.GA25036-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-05-02 17:22                           ` Eric W. Biederman
2017-05-02 17:33                           ` Kirill Tkhai
     [not found]                             ` <de392430-18b8-d296-b868-82fdedcd0c0e-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
2017-05-02 21:13                               ` Eric W. Biederman
     [not found]                                 ` <8737cngdxi.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-05-03 10:20                                   ` Kirill Tkhai
2017-04-27 16:39                   ` Eric W. Biederman
     [not found]                     ` <87o9vhztwv.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-04-28  9:22                       ` Kirill Tkhai
2017-04-27 16:16           ` Oleg Nesterov

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