netdev - Re: [PATCH net-next 09/17] net: Allow userns root control of the core of the network stack.

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Message-ID: <871uft8vpm.fsf@xmission.com>
Date:	Fri, 16 Nov 2012 06:32:21 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Glauber Costa <glommer@...allels.com>
Cc:	David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next 09/17] net: Allow userns root control of the core of the network stack.

Glauber Costa <glommer@...allels.com> writes:

> On 11/16/2012 05:03 PM, Eric W. Biederman wrote:
>> +	if (!capable(CAP_NET_ADMIN))
>> +		return -EPERM;
>> +
>>  	return netdev_store(dev, attr, buf, len, change_tx_queue_len);
>
> You mean ns_capable here?

No.  There I meant capable.

I deliberately call capable here because I don't understand what
the tx_queue_len well enough to be certain it is safe to relax
that check to be just ns_capable.

My get feel is that allowing an unprivileged user to be able to
arbitrarily change the tx_queue_len on a networking device would be a
nice way to allow queuing as many network packets as you would like with
kernel memory and DOSing the machine.

So since with a quick read of the code I could not convince myself it
was safe to allow unprivilged users to change tx_queue_len I left it
protected by capable.  While at the same time I relaxed the check in
netdev_store to be ns_capable.

Eric

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