linux-kernel - Re: [PATCH] namespace:unmount pid_namespace's proc_mnt when copy_net

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Date:	Fri, 02 Nov 2012 15:33:15 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [PATCH] namespace:unmount pid_namespace's proc_mnt when copy_net_ns
 failed

于 2012年11月02日 15:02, Eric W. Biederman 写道:
> Gao feng <gaofeng@...fujitsu.com> writes:
> 
>> we should call pid_ns_release_proc to unmount pid_namespace's
>> proc_mnt when copy_net_ns failed in function create_new_namespaces.
>>
>> otherwise,the proc_mnt will not be freed and because the super_block
>> of proc_mnt also add the reference of the pid_namespace,so this
>> pid_namespace will never be released too.
> 
> Ouch!
> 
> Have you encountered this failure in practice or is this just from
> review?

I add some printk in pid_ns_release_proc,it's not called in above case.
when copy_net_ns failed,this pid_namespace is not used by any task,
so proc_flush_task can't call pid_ns_release_proc to umount this pidns->proc_mnt.
it's the only chance we can unmount this pindns->proc_mnt.

With this patch,everything runs well.

Thanks
Gao

> 
> I'm trying to gauge the severity of this leak.
> 
> Eric
> 
> 
>> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
>> ---
>>  kernel/nsproxy.c |    5 ++++-
>>  1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
>> index b576f7f..d536480 100644
>> --- a/kernel/nsproxy.c
>> +++ b/kernel/nsproxy.c
>> @@ -99,8 +99,11 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
>>  	return new_nsp;
>>  
>>  out_net:
>> -	if (new_nsp->pid_ns)
>> +	if (new_nsp->pid_ns) {
>> +		if (flags & CLONE_NEWPID)
>> +			pid_ns_release_proc(new_nsp->pid_ns);
>>  		put_pid_ns(new_nsp->pid_ns);
>> +	}
>>  out_pid:
>>  	if (new_nsp->ipc_ns)
>>  		put_ipc_ns(new_nsp->ipc_ns);
> --
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