pfil on bridge interface, looking for ether_header

[Kevin Sanders]

On 11/2/06, Andrew Thompson <thompsa at freebsd.org> wrote:
> On Thu, Nov 02, 2006 at 05:45:50PM -0800, Kevin Sanders wrote:
> > I've written a kernel module that has pfil_add_hook'ed into the pfil
> > framework.  When my input packet filter function is called, I can
> > mtod(*m, struct IP *) to the IP header, but haven't found a way to
> > find the original ethernet header.
>
> If you look in if_bridge.c:bridge_pfil you will see that the ethernet
> header is stripped from the mbuf before passing to pfil. You may want to
> create another hook such as ether_pfil_hook and modify the bridge to use
> it. Alternatively see the recent discussion between Julian and Andre on
> the matter.

I've got a simple fix for this that solves my immediate need (to be
able to reach the ethernet header).  I grepped around, and don't see
much use of the m_pkthdr.header value anymore, and this doesn't appear
to break anything yet.

*** if_bridge.c	21 Oct 2006 12:10:39 -0700	1.11.2.40
--- if_bridge.c	03 Nov 2006 11:46:15 -0800	
***************
*** 2781,2786 ****
--- 2781,2787 ----

  ipfwpass:
  	error = 0;
+ 	(*mp)->m_pkthdr.header = &eh2;

  	/*
  	 * Run the packet through pfil
***************
*** 2902,2907 ****
--- 2903,2909 ----
  	if (*mp == NULL)
  		return (error);
  	bcopy(&eh2, mtod(*mp, caddr_t), ETHER_HDR_LEN);
+ 	(*mp)->m_pkthdr.header = NULL;

  	return (0);