netdev - Re: [PATCH] net:ppp: replace too strict capability restriction on opening /dev/ppp

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Date:	Sun, 19 Jun 2016 12:40:49 +0200
From:	Richard Weinberger <richard@....at>
To:	Shanker Wang <miao.wang@...a.tsinghua.edu.cn>
Cc:	netdev@...r.kernel.org,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Guillaume Nault <g.nault@...halink.fr>
Subject: Re: [PATCH] net:ppp: replace too strict capability restriction on
 opening /dev/ppp

Am 19.06.2016 um 12:36 schrieb Shanker Wang:
> 
>> 在 2016年6月19日，12:13，Richard Weinberger <richard@....at> 写道：
>>
>> Am 19.06.2016 um 07:21 schrieb Shanker Wang:
>>> This patch removes the check for CAP_NET_ADMIN in the initial namespace
>>> when opening /dev/open. Instead, CAP_NET_ADMIN is checked in the user
>>> namespace the net namespace was created so that /dev/ppp cat get opened
>>> in a unprivileged container.
>>>
>>> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
>>> Cc: Richard Weinberger <richard.weinberger@...il.com>
>>> Cc: Guillaume Nault <g.nault@...halink.fr>
>>> Cc: Miao Wang <shankerwangmiao@...il.com>
>>> Signed-off-by: Miao Wang <miao.wang@...a.tsinghua.edu.cn>
>>> ---
>>> drivers/net/ppp/ppp_generic.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
>>> index f572b31..4b3b2b5 100644
>>> --- a/drivers/net/ppp/ppp_generic.c
>>> +++ b/drivers/net/ppp/ppp_generic.c
>>> @@ -380,7 +380,7 @@ static int ppp_open(struct inode *inode, struct file *file)
>>> 	/*
>>> 	 * This could (should?) be enforced by the permissions on /dev/ppp.
>>> 	 */
>>> -	if (!capable(CAP_NET_ADMIN))
>>> +	if (!ns_capable(current->nsproxy->net_ns->user_ns, CAP_NET_ADMIN))
>>> 		return -EPERM;
>>
>> Shouldn't this be a ns_capable(net->user_ns, …?
>> Otherwise an user can create a new user_ns followed by a new net_ns and has
>> CAP_NET_ADMIN. We need to check whether he is allowed in the user_ns of the
>> net_ns which belongs to the ppp net device which you want to open.
> You are totally right. However, I wonder how can i get the “net” struct when 
> opening /dev/ppp

I'm sure you can get it somehow via file->private_data.

Thanks,
//richard