Subject: Re: Netlink mmap tx security?

From: Daniel Borkmann <[email-masked]>
Date: Thu, 16 Oct 2014 08:45:44 +0200

On 10/15/2014 04:09 AM, David Miller wrote:
> From: Andy Lutomirski <[email-masked]>
> Date: Tue, 14 Oct 2014 19:03:11 -0700
>
>> On Tue, Oct 14, 2014 at 7:01 PM, David Miller <[email-masked]> wrote:
>>> I really think this means I'll have to remove all of the netlink
>>> mmap() support in order to prevent from breaking applications. :(
>>>
>>> The other option is to keep NETLINK_TX_RING, but copy the data into
>>> a kernel side buffer before acting upon it.
>>
>> Option 3, which sucks but maybe not that badly: change the value of
>> NETLINK_RX_RING.  (Practically: add NETLINK_RX_RING2 or something like
>> that.)
>
> That would work as well.
>
> There are pros and cons to all of these approaches.
>
> I was thinking that if we do the "TX mmap --> copy to kernel buffer"
> approach, then if in the future we find a way to make it work
> reliably, we can avoid the copy.  And frankly performance wise it's no
> worse than what happens via normal sendmsg() calls.
>
> And all applications using NETLINK_RX_RING keep working and keep
> getting the performance boost.

That would be better, yes. This would avoid having such a TPACKET_V*
API chaos we have in packet sockets if this could be fixed for netlink
eventually.