DragonFly BSD
DragonFly bugs List (threaded) for 2005-01
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Re: IPFW2 layer2 filtering broken - PATCH

From: Jeffrey Hsu <hsu@xxxxxxxxxxx>
Date: Mon, 24 Jan 2005 11:12:11 -0800

Joerg Sonnenberger wrote:
On Mon, Jan 24, 2005 at 09:50:05AM -0800, Matthew Dillon wrote:

From my read of the code, the 'eh = mtod(...)' is necessary, but most of the time the returned 'm' will be the same as the passed 'm'
so I am not surprised that you did not see any difference.

The eh = mtod() is necessary, because the ether header might not actually be
part of the passed in header. Because ether_ifpw_chk changes that by
prepending the header, it is necessary to update the pointer in the caller.

This is an interface problem. When ether_ipfw_chk() does not modify the mbuf, the recomputed eh pointer is incorrect because the mbuf has already been adjusted. An ugly workaround is something like

       if (IPFW_LOADED && ether_ipfw != 0) {
+               struct mbuf *n = m;
               if (!ether_ipfw_chk(&m, NULL, &rule, eh, FALSE)) {
-               eh = mtod(m, struct ether_header *);
+               if (m != n)
+                       eh = mtod(m, struct ether_header *);

Alternatively, we could change the 4th parameter to ether_ipfw_chk()
to &eh and update it inside ether_ipfw_chk().

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