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

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Message-ID: <5766704C.6060309@nod.at>
Date:	Sun, 19 Jun 2016 12:13:32 +0200
From:	Richard Weinberger <richard@....at>
To:	Shanker Wang <miao.wang@...a.tsinghua.edu.cn>,
	netdev@...r.kernel.org
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Guillaume Nault <g.nault@...halink.fr>,
	王邈 <shankerwangmiao@...il.com>
Subject: Re: [PATCH] net:ppp: replace too strict capability restriction on
 opening /dev/ppp

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.

Thanks,
//richard