netdev - Re: bug in passing file descriptors

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Message-Id: <20131007.151233.2237348893254566536.davem@davemloft.net>
Date:	Mon, 07 Oct 2013 15:12:33 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sar@...-labs.com
Cc:	luto@...capital.net, netdev@...r.kernel.org,
	mtk.manpages@...il.com, ebiederm@...ssion.com
Subject: Re: bug in passing file descriptors

From: Steve Rago <sar@...-labs.com>
Date: Mon, 7 Oct 2013 15:06:02 -0400

> Maybe.  So a client expecting to receive x bytes of control
> information should make sure their buffer is at least CMSG_SPACE(x)
> bytes long instead of CMSG_LEN(x) bytes long, because you feel
> compelled to copy the final padding from kernel space to user space?
> Seems wrong to me.  IMHO, the final padding should only come into play
> when calculating where the next header should begin.

Yes, all control messages must be aligned to, and be of a length of a
multiple of, "sizeof(long)".

This is the only correct way to program control messages.
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