netdev - Re: Netlink mmap tx security?

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Message-Id: <20141014.220908.123550384430402000.davem@davemloft.net>
Date:	Tue, 14 Oct 2014 22:09:08 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	luto@...capital.net
Cc:	torvalds@...ux-foundation.org, kaber@...sh.net,
	netdev@...r.kernel.org, tgraf@...g.ch
Subject: Re: Netlink mmap tx security?

From: Andy Lutomirski <luto@...capital.net>
Date: Tue, 14 Oct 2014 19:03:11 -0700

> On Tue, Oct 14, 2014 at 7:01 PM, David Miller <davem@...emloft.net> 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.

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