From owner-freebsd-hackers  Tue Mar 27 23:35:12 2001
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To: Brian Somers <brian@Awfulhak.org>
Cc: David Malone <dwmalone@maths.tcd.ie>,
	freebsd-hackers@freebsd.org, freebsd-alpha@freebsd.org,
	wpaul@freebsd.org
Subject: Re: Control messages. 
In-reply-to: Your message of "Tue, 27 Mar 2001 17:41:19 BST."
             <200103271641.f2RGfJL00975@hak.lan.Awfulhak.org> 
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Date: Wed, 28 Mar 2001 08:34:53 +0100
From: David Malone <dwmalone@maths.tcd.ie>
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> I can't see where in the kernel we're *not* using CMSG_DATA().  This 
> was fixed a while ago and tested ok on beast (for 3 descriptors 
> AFAIR).  Are we looking at the same code (I'm looking in /sys/kern) ?

Have a look in uipc_usrreq.c:unp_internalize(), it uses (cm+1) to
find where the data is to be written out in the CREDS case and uses
(cm+1) to find where the descriptors start in the RIGHTS case. The
reallocation code seems to be broken (it attaches a cluster to a
mbuf it is still using, currupting the data in the mbuf). If I
enable it on the 386, where it is unnecessaey usually, and pass
about 50 discriptors I get a panic.

I've had a look at what other people have done about this issue.
The NetBSD people seem to have taken the fix I'm proposing. Solaris
and BSD/OS don't provide the required alignment and just define
CMSG_DATA(cm) to be (cm+1).

	David.

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