netdev - Re: [Security] TIPC security issues

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Date:	Wed, 27 Oct 2010 10:37:46 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	drosenberg@...curity.com, jon.maloy@...csson.com,
	allan.stephens@...driver.com, netdev@...r.kernel.org,
	security@...nel.org
Subject: Re: [Security] TIPC security issues

On Wed, Oct 27, 2010 at 10:29 AM, David Miller <davem@...emloft.net> wrote:
>
> But for a datagram socket, we have to have a one-to-one correspondance
> between write() calls and packets on the wire.  So we'd either need to
> accept the entire write() length or fail it with an error.

I disagree. We had that exact issue with regular file read/write: in
theory, POSIX says that you should never do a partial write to a
regular file.

And the thing is, WE SIMPLY DON'T CARE. If somebody does a 2GB+ IO,
they damn well need to accept that it's not going to be some atomic
single event. It doesn't matter _how_ much actual real memory you
have, it's just stupid to even care about that situation. It's not
something any real app actually can reasonably ever expect to work, so
rather than say "we have to do it right or error out", you should just
see it as a "it's a stupid situation, we can do whatever the hell we
want, because anybody who cares is a f*cking moron that we don't care
about".

If you _really_ care deeply, then some packet-oriented protocol can
just have its own private packet size limit (which would be way less
than 2GB), and then just look at the total size and say "oh, the total
size is bigger than my limit, so I'll just error out". Then, the fact
that verify_iovec() may have truncated the message to 2GB-1 doesn't
matter at all.

(Practically speaking, I bet all packet-oriented protocols already
have a limit that is enforced by simply allocation patterns, so I
don't think it's actually a problem even now)

                   Linus
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