netdev - Re: nf_conntrack: Infoleak via CTA_ID and CTA_EXPECT

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Date:   Fri, 30 Jun 2017 21:45:53 +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 30.06.2017 um 21:35 schrieb Florian Westphal:
> Richard Weinberger <richard@....at> wrote:
>> Hi!
>>
>> I noticed that nf_conntrack leaks kernel addresses, it uses the memory address
>> as identifier used for generating conntrack and expect ids..
>> Since these ids are also visible to unprivileged users via network namespaces
>> I suggest reverting these commits:
> 
> Why not use a hash of the address?

Would also work. Or xor it with a random number.

On the other hand, for user space it would be more useful when the conntrack id
does not repeat that often. That's why I favor the good old counter method.
Currently the conntrack id is reused very fast.
e.g. in one of our applications we use the conntack id via NFQUEUE and watch the
destroy events via conntrack. It happens regularly that a new connection has the
same id than a different connection we saw some moments before, before we receive
the destroy event from the conntrack socket.

Thanks,
//richard