linux-kernel - Re: [PATCH 1/1] pid_ns: move pid_ns_release_proc() from proc_flush_task() to zap_pid_ns

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Date:	Thu, 24 Jun 2010 00:06:57 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Louis Rilling <louis.rilling@...labs.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/1] pid_ns: move pid_ns_release_proc() from proc_flush_task() to zap_pid_ns_processes()

Oleg Nesterov <oleg@...hat.com> writes:

> This is mostly cleanup and optimization, but also fixes the bug.

Oleg with respect to your other patches I think they are some of
the best ones we have on the table.

> proc_flush_task() checks upid->nr == 1 to detect the case when
> a sub-namespace exits. However, this doesn't work in case when
> a multithreaded init execs and calls release_task(old_leader),
> the old leader has the same pid 1.
>
> Move pid_ns_release_proc() to zap_pid_ns_processes(), it is called
> when we know for sure that init is exiting.

This actually guarantees a use after free for the namespace init:

do_exit()
   exit_notify()
      forget_original_parent()
         find_new_reaper()
            zap_pid_ns_processes()
release_task()
   proc_flush_task()

> Note: with or without this change this mntput() can happen before the
> EXIT_DEAD tasks not visible to do_wait() have passed proc_flush_task().
> We need more fixes.

I agree.

Eric


> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>
>  fs/proc/base.c         |    4 ----
>  kernel/pid_namespace.c |    2 ++
>  2 files changed, 2 insertions(+), 4 deletions(-)
>
> --- 35-rc3/fs/proc/base.c~PNS_5_MOVE_MNTPUT_TO_ZAP	2010-06-23 22:06:01.000000000 +0200
> +++ 35-rc3/fs/proc/base.c	2010-06-23 22:10:26.000000000 +0200
> @@ -2745,10 +2745,6 @@ void proc_flush_task(struct task_struct 
>  		proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
>  					tgid->numbers[i].nr);
>  	}
> -
> -	upid = &pid->numbers[pid->level];
> -	if (upid->nr == 1)
> -		pid_ns_release_proc(upid->ns);
>  }
>  
>  static struct dentry *proc_pid_instantiate(struct inode *dir,
> --- 35-rc3/kernel/pid_namespace.c~PNS_5_MOVE_MNTPUT_TO_ZAP	2010-06-23 22:13:07.000000000 +0200
> +++ 35-rc3/kernel/pid_namespace.c	2010-06-23 22:13:55.000000000 +0200
> @@ -189,6 +189,8 @@ void zap_pid_ns_processes(struct pid_nam
>  	} while (rc != -ECHILD);
>  
>  	acct_exit_ns(pid_ns);
> +	pid_ns_release_proc(pid_ns);
> +
>  	return;
>  }
>  
--
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