linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Aaron Tomlin <atomlin@redhat.com>,
	Pavel Emelyanov <xemul@parallels.com>,
	Serge Hallyn <serge.hallyn@ubuntu.com>,
	Sterling Alexander <stalexan@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] exit: pidns: alloc_pid() leaks pid_namespace if child_reaper is exiting
Date: Tue, 25 Nov 2014 18:07:18 +0100	[thread overview]
Message-ID: <20141125170718.GA29360@redhat.com> (raw)
In-Reply-To: <87vbm4ff0r.fsf@x220.int.ebiederm.org>

On 11/24, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > --- a/kernel/pid.c
> > +++ b/kernel/pid.c
> > @@ -320,7 +320,6 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> >  			goto out_free;
> >  	}
> >
> > -	get_pid_ns(ns);
> >  	atomic_set(&pid->count, 1);
> >  	for (type = 0; type < PIDTYPE_MAX; ++type)
> >  		INIT_HLIST_HEAD(&pid->tasks[type]);
> > @@ -336,7 +335,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> >  	}
> >  	spin_unlock_irq(&pidmap_lock);
> >
> > -out:
> > +	get_pid_ns(ns);
>
> Moving the label and changing the goto out logic is gratuitous confusing
> and I think it probably even generates worse code.
>
> Furthermore multiple exits make adding debugging code more difficult.

Oh, I strongly disagree but I am not going to argue ;) cleanups are
always subjective, and I do believe in "maintainer is always right"
mantra. I can make v2 without this change.

> Moving get_pid_ns down does close a leak in the error handling path.

OK, good.

> However at the moment my I can't figure out if it is safe to move
> get_pid_ns elow hlist_add_head_rcu.  Because once we are on the rcu list
> the pid is findable, and being publicly visible with a bad refcount could cause
> problems.

The caller has a reference, this ns can't go away. Obviously, otherwise
get_pid_ns(ns) is not safe.

We need this get_pid_ns() to balance put_pid()->put_pid_ns() which obviously
won't be called until we return this pid, otherwise everything is wrong.

So I think this should be safe?

Oleg.


  reply	other threads:[~2014-11-25 17:07 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-11-07 20:14 [PATCH 0/4] proc: deuglify task_state() Oleg Nesterov
2014-11-07 20:14 ` [PATCH 1/4] proc: task_state: read cred->group_info outside of task_lock() Oleg Nesterov
2014-11-07 20:14 ` [PATCH 2/4] proc: task_state: deuglify the max_fds calculation Oleg Nesterov
2014-11-07 20:14 ` [PATCH 3/4] proc: task_state: move the main seq_printf() outside of rcu_read_lock() Oleg Nesterov
2014-11-13 18:04   ` Paul E. McKenney
2014-11-07 20:14 ` [PATCH 4/4] proc: task_state: ptrace_parent() doesn't need pid_alive() check Oleg Nesterov
2014-11-10 21:59 ` [PATCH 0/5] exit: reparent zombie fix + cleanups/optimizations Oleg Nesterov
2014-11-10 22:00   ` [PATCH 1/5] sched_show_task: fix unsafe usage of ->real_parent Oleg Nesterov
2014-11-11 10:39     ` Peter Zijlstra
2014-11-10 22:00   ` [PATCH 2/5] exit: reparent: use ->ptrace_entry rather than ->sibling for EXIT_DEAD tasks Oleg Nesterov
2014-11-10 22:00   ` [PATCH 3/5] exit: reparent: cleanup the changing of ->parent Oleg Nesterov
2014-11-10 22:00   ` [PATCH 4/5] exit: reparent: cleanup the usage of reparent_leader() Oleg Nesterov
2014-11-10 22:00   ` [PATCH 5/5] exit: ptrace: shift "reap dead" code from exit_ptrace() to forget_original_parent() Oleg Nesterov
2014-11-14  1:37 ` [PATCH 0/5] exit: more cleanups/optimizations Oleg Nesterov
2014-11-14  1:38   ` [PATCH 1/5] exit: wait: cleanup the ptrace_reparented() checks Oleg Nesterov
2014-11-14  1:38   ` [PATCH 2/5] exit: wait: don't use zombie->real_parent Oleg Nesterov
2014-11-14  1:38   ` [PATCH 3/5] exit: wait: drop tasklist_lock before psig->c* accounting Oleg Nesterov
2014-11-14  1:38   ` [PATCH 4/5] exit: release_task: fix the comment about group leader accounting Oleg Nesterov
2014-11-14  1:38   ` [PATCH 5/5] exit: proc: don't try to flush /proc/tgid/task/tgid Oleg Nesterov
2014-11-18 21:29 ` [PATCH 0/6] exit: find_new_reaper() fixes/cleanups Oleg Nesterov
2014-11-18 21:30   ` [PATCH 1/6] exit: reparent: fix the dead-parent PR_SET_CHILD_SUBREAPER reparenting Oleg Nesterov
2014-11-18 21:30   ` [PATCH 2/6] exit: reparent: fix the cross-namespace " Oleg Nesterov
2014-11-18 21:30   ` [PATCH 3/6] exit: reparent: s/while_each_thread/for_each_thread/ in find_new_reaper() Oleg Nesterov
2014-11-18 21:30   ` [PATCH 4/6] exit: reparent: document the ->has_child_subreaper checks Oleg Nesterov
2014-11-18 21:30   ` [PATCH 5/6] exit: reparent: introduce find_child_reaper() Oleg Nesterov
2014-11-18 21:30   ` [PATCH 6/6] exit: reparent: introduce find_alive_thread() Oleg Nesterov
2014-11-20 18:34 ` [PATCH 0/3] exit: avoid O(n ** 2) thread-list scan on group-exit if possible Oleg Nesterov
2014-11-20 18:34   ` [PATCH -mm 1/3] exit: reparent: avoid find_new_reaper() if no children Oleg Nesterov
2014-11-20 22:37     ` Andrew Morton
2014-11-21 20:01       ` Oleg Nesterov
2014-11-20 18:34   ` [PATCH -mm 2/3] exit: reparent: call forget_original_parent() under tasklist_lock Oleg Nesterov
2014-11-20 18:34   ` [PATCH -mm 3/3] exit: exit_notify: re-use "dead" list to autoreap current Oleg Nesterov
2014-11-24 20:06 ` [PATCH 0/2] exit/pid_ns: comments + simple fix Oleg Nesterov
2014-11-24 20:06   ` [PATCH 1/2] exit: reparent: fix/update the comments in zap_pid_ns_processes() Oleg Nesterov
2014-11-24 20:14     ` Oleg Nesterov
2014-11-24 22:07     ` Eric W. Biederman
2014-11-25 16:57       ` Oleg Nesterov
2014-11-25 17:17         ` Oleg Nesterov
2014-11-24 20:06   ` [PATCH 2/2] exit: pidns: alloc_pid() leaks pid_namespace if child_reaper is exiting Oleg Nesterov
2014-11-24 21:46     ` Eric W. Biederman
2014-11-25 17:07       ` Oleg Nesterov [this message]
2014-11-25 17:50         ` Eric W. Biederman
2014-11-25 18:15           ` Oleg Nesterov
2014-11-25 18:43             ` Eric W. Biederman
2014-11-25 18:59               ` Oleg Nesterov
2014-11-24 21:27   ` [PATCH 0/2] exit/pid_ns: comments + simple fix Eric W. Biederman
2014-11-24 21:38     ` Oleg Nesterov
2014-11-24 21:48   ` Eric W. Biederman
2014-11-25 16:57     ` Oleg Nesterov
2014-11-26 23:54   ` [PATCH v2 " Oleg Nesterov
2014-11-26 23:54     ` [PATCH v2 1/2] exit: pidns: alloc_pid() leaks pid_namespace if child_reaper is exiting Oleg Nesterov
2014-11-27 15:44       ` Eric W. Biederman
2014-11-26 23:54     ` [PATCH v2 2/2] exit: pidns: fix/update the comments in zap_pid_ns_processes() Oleg Nesterov
2014-12-01 22:39       ` Andrew Morton
2014-12-01 23:24         ` Oleg Nesterov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20141125170718.GA29360@redhat.com \
    --to=oleg@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=atomlin@redhat.com \
    --cc=ebiederm@xmission.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=serge.hallyn@ubuntu.com \
    --cc=stalexan@redhat.com \
    --cc=xemul@parallels.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).