netdev - Re: nf_conntrack: Infoleak via CTA_ID and CTA_EXPECT

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Message-ID: <1daf1401-5009-df1c-a77a-a271811c0760@nod.at>
Date:   Wed, 12 Jul 2017 23:26:35 +0200
From:   Richard Weinberger <richard@....at>
To:     Florian Westphal <fw@...len.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        David Miller <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        David Gstir <david@...ma-star.at>, kaber@...sh.net,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: Re: nf_conntrack: Infoleak via CTA_ID and CTA_EXPECT_ID

Florian,

Am 01.07.2017 um 12:35 schrieb Florian Westphal:
>>> Perhaps we can place that in a new extension (its not needed in any
>>> fastpath ops)?
>>
>> To get rid of the infoleak we have to re-introduce the id field in struct nf_conn
>> and struct nf_conntrack_expect.
> 
> Why will this not work?

You are right, when we compute the ID from the whole object, it should be fine.

>> Otherwise have nothing to compare against in the conntrack/expect remove case.
> 
> Not following, sorry.  The id is not used anywhere except when we send
> info to userspace.
> 
> The compare on removal is not needed afaics, and its also not used when
> doing lookup to begin with, so we can just recompute it?

Isn't this a way too much overhead?

I personally favor Pablo's per-cpu counter approach.
That way the IDs are unique again and we get rid of the info leak without
much effort.

Thanks,
//richard