Subject: Re: bugs caused by M_LEADINGSPACE() semantic change
To: None <firstname.lastname@example.org>
From: Jason R Thorpe <email@example.com>
Date: 11/07/2002 18:26:09
On Fri, Nov 08, 2002 at 11:14:06AM +0900, firstname.lastname@example.org wrote:
> >Modified Files:
> > syssrc/sys/netinet: raw_ip.c
> >Log Message:
> >In the IP_HDRINCL case of rip_output(), if the mbuf is read-only
> >then copy the header into a new mbuf before modifying it.
> >Fixes PR 18809. Thanks to Chuq Silvers for diagnosing it.
> i guess we should modify M_PREPEND() to make sure the new portion
> is read/write. how does it sound?
That wasn't the problem. M_PREPEND() does, in fact, do a read/write
check, because it uses M_LEADINGSPACE(), which uses M_READONLY().
Besides, M_PREPEND() is only used in the non-IP_HDRINCL case. That
case works fine.
The problem was the IP_HDRINCL case, which does NOT use M_PREPEND().
Instead, since the header is already there (no need to prepend it),
it just put ip_len and ip_off in network order, and set ip_id. Those
modifications of the buffer need to be protected with an M_READONLY()
check, which is what I added.
-- Jason R. Thorpe <email@example.com>