linux-kernel - Re: [PATCH v2] unix: properly account for FDs passed over unix sockets

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Date:	Tue, 2 Feb 2016 11:29:59 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	David Herrmann <dh.herrmann@...il.com>, Willy Tarreau <w@....eu>,
	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Марк Коренберг 
	<socketpair@...il.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Simon McVittie <simon.mcvittie@...labora.co.uk>
Subject: Re: [PATCH v2] unix: properly account for FDs passed over unix sockets

On Tue, Feb 2, 2016 at 10:29 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
>>
>> Anyway, can someone provide a high-level description of what exactly
>> this patch is supposed to do? Which operation should be limited, who
>> should inflight FDs be accounted on, and which rlimit should be used
>> on each operation? I'm having a hard time auditing existing
>> user-space, given just the scarce description of this commit.
>
> Yes, all your observations are true. I think we need to explicitly
> need to refer to the sending socket while attaching the fds.

I don't think that really helps. Maybe somebody passed a unix domain
socket around, and now we're crediting the wrong socket again.

So how about we actually add a "struct cred *" to the scm_cookie
itself, and we initialize it to "get_current_cred()". And then always
use that.

That way it's always the person who actually does the send (rather
than the opener of the socket _or_ the opener of the file that gets
passed around) that gets credited, and thanks to the cred pointer we
can then de-credit them properly.

Hmm?

                Linus