netdev - Re: [PATCH v3] ip6_output: ensure flow saddr actually belongs to device

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Message-ID: <0214eaf8-70c6-5a37-cddd-faa1c4268871@cumulusnetworks.com>
Date:   Mon, 14 Nov 2016 10:48:01 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Netdev <netdev@...r.kernel.org>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        LKML <linux-kernel@...r.kernel.org>,
        YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Subject: Re: [PATCH v3] ip6_output: ensure flow saddr actually belongs to
 device

On 11/14/16 10:33 AM, Hannes Frederic Sowa wrote:
>>>>> I just also quickly read up on the history (sorry was travelling last
>>>>> week) and wonder if you ever saw a user space facing bug or if this is
>>>>> basically some difference you saw while writing out of tree code?
>>>>
>>>> I checked the userspace API this morning. bind and cmsg for example check that the address is valid with calls to ipv6_chk_addr.
>>>
>>> Hmm, so it fixes no real bug.
>>>
>>> Because of translations of flowi6_oif we actually can't do a correct
>>> check of source address for cases like the one I outlined above? Hmm,
>>> maybe we should simply depend on user space checks.
>>
>> I believe Jason's case is forwarding path and the ipv6_stub->ipv6_dst_lookup API.
> 
> It is not a kernel API, because we don't support something like that for
> external kernel modules. We basically exported ipv6_dst_lookup to allow
> some IPv4 code to do ipv6 stunts when the IPv6 module is loaded. ;)

???

ipv6_stub is exported for modules (EXPORT_SYMBOL_GPL(ipv6_stub)).

ipv6_stub->ipv6_dst_lookup is used by several modules -- geneve, tipc, vxlan, mpls -- for IPv6 lookups, not IPv4 code do IPv6 stunts.

So how do you say that is not an exported kernel API?