From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: bug in passing file descriptors
Date: Mon, 07 Oct 2013 15:12:33 -0400 (EDT)
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From: Steve Rago <sar@nec-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.