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

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Message-Id: <C708B373-7946-458A-A4C2-BB63A2413FB6@tuna.tsinghua.edu.cn>
Date:	Sun, 19 Jun 2016 12:36:36 +0200
From:	Shanker Wang <miao.wang@...a.tsinghua.edu.cn>
To:	Richard Weinberger <richard@....at>
Cc:	netdev@...r.kernel.org,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Guillaume Nault <g.nault@...halink.fr>
Subject: Re: [PATCH] net:ppp: replace too strict capability restriction on opening /dev/ppp


> 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
> 
> Thanks,
> //richard