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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Christian Brauner <christian.brauner@canonical.com>
Cc:     Jiri Benc <jbenc@redhat.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        netdev@vger.kernel.org, ktkhai@virtuozzo.com,
        stephen@networkplumber.org, w.bumiller@proxmox.com,
        nicolas.dichtel@6wind.com, linux-kernel@vger.kernel.org,
        dsahern@gmail.com, davem@davemloft.net
References: <20180206131902.31937-1-christian.brauner@ubuntu.com>
        <20180206131902.31937-2-christian.brauner@ubuntu.com>
        <20180207121925.5fa1e534@redhat.com>
        <20180207115050.GA29047@gmail.com>
Date:   Wed, 07 Feb 2018 09:20:32 -0600
In-Reply-To: <20180207115050.GA29047@gmail.com> (Christian Brauner's message
        of "Wed, 7 Feb 2018 12:50:51 +0100")
Message-ID: <878tc4g727.fsf@xmission.com>
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Subject: Re: [PATCH net 1/1 v3] rtnetlink: require unique netns identifier
Sender: linux-kernel-owner@vger.kernel.org
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Christian Brauner <christian.brauner@canonical.com> writes:

> On Wed, Feb 07, 2018 at 12:19:25PM +0100, Jiri Benc wrote:
>> On Tue,  6 Feb 2018 14:19:02 +0100, Christian Brauner wrote:
>> > +/* Verify that rtnetlink requests supporting network namespace ids
>> > + * do not pass additional properties potentially referring to different
>> > + * network namespaces.
>> > + */
>> > +static int rtnl_ensure_unique_netns(struct nlattr *tb[],
>> > +				    struct netlink_ext_ack *extack)
>> > +{
>> > +	/* Requests without network namespace ids have been able to specify
>> > +	 * multiple properties referring to different network namespaces so
>> > +	 * don't regress them.
>> > +	 */
>> > +	if (!tb[IFLA_IF_NETNSID])
>> > +		return 0;
>> 
>> I agree with Eric that we should enforce this also for the existing
>> pid/fd attributes.
>
> Yes, I would prefer this too but in the Linux spirit of never regressing
> userspace I was afraid that there might already be userspace
> applications that stick a pid and an fd at the same time into an
> rtnetlink request. If we are ok with potentially breaking them then we
> should just go for it. It is definitely the cleaner solution.

Odds are low that anything does anything so silly.  If we accidentally
cause a regression then we fix it.  Unless you have reason to suspect
someone actually does something silly we should be good.

Eric